Editing Opiliones

{{Short description|Order of arachnids}}
{{For-multi|other arthropods called "daddy longlegs", and other uses|Daddy longlegs (disambiguation)|the novel by Jean Webster|Daddy-Long-Legs (novel)}}
{{Automatic taxobox
| taxon = Opiliones
| fossil_range = {{Fossil range|410|0|earliest=473}}<small>Early [[Devonian]] – [[Holocene]]</small>
| image = Opiliones harvestman.jpg
| image_upright = 1.2
| image_caption = ''[[Hadrobunus grandis]]'' showing its body structure and long legs: one pair of eyes and broadly joined body tagma differentiate it from similar-looking arachnids.
| authority = [[Carl Jakob Sundevall|Sundevall]], 1833
| diversity_link = 
| diversity = 5 suborders, > 6,650 species
| subdivision_ranks = Suborders
| subdivision = *[[Cyphophthalmi]]
*[[Eupnoi]]
*[[Dyspnoi]]
*[[Laniatores]]
*†[[Tetrophthalmi]]
}}

The '''Opiliones''' (formerly Phalangida) are an [[Order (biology)|order]] of [[arachnid]]s,
[[Common name|colloquially]] known as '''harvestmen''', '''harvesters''', '''harvest spiders''', or '''daddy longlegs''' (see {{slink||Etymology}} below). {{As of|July 2024}}, over 6,650 species of harvestmen have been discovered worldwide,<ref name="WCO-lite" /><ref>{{Cite web|url=http://www.museunacional.ufrj.br/mndi/Aracnologia/opiliones.html|title=Classification of Opiliones|last=Kury|first=Adriano B.|website=www.museunacional.ufrj.br|access-date=2017-11-29}}</ref><ref name="Hallan" /> although the total number of [[extant taxon|extant]] species may exceed 10,000.<ref name=pinto>{{cite book |author=Glauco Machado, Ricardo Pinto-da-Rocha & Gonzalo Giribet |chapter=What are harvestmen? |pages=1–13 |editor=Ricardo Pinto-da-Rocha, Glauco Machado & Gonzalo Giribet |title=Harvestmen: the Biology of Opiliones |year=2007 |publisher=[[Harvard University Press]] |isbn=978-0-674-02343-7}}</ref> The order Opiliones includes five suborders: [[Cyphophthalmi]], [[Eupnoi]], [[Dyspnoi]], [[Laniatores]], and [[Tetrophthalmi]], which were named in 2014.<ref name=Tetro />

Representatives of each extant suborder can be found on all continents except [[Antarctica]].

Well-preserved fossils have been found in the 400-million-year-old [[Rhynie chert]]s of Scotland, and 305-million-year-old rocks in France. These fossils look surprisingly modern, indicating that their basic body shape developed very early on,<ref name=Mont>{{cite journal|title=Anatomically modern Carboniferous harvestmen demonstrate early cladogenesis and stasis in Opiliones|first1=Russell J.|last1=Garwood|first2=Jason A.|last2=Dunlop|first3=Gonzalo|last3=Giribet|first4=Mark D.|last4=Sutton|year=2011|journal=Nature Communications|volume=2|pages=444|doi=10.1038/ncomms1458|pmid=21863011|bibcode=2011NatCo...2..444G|doi-access=free}}</ref> and, at least in some taxa, has changed little since that time.

Their [[Phylogenetics|phylogenetic]] position within the Arachnida is disputed; their closest relatives may be camel spiders ([[Solifugae]]) or a larger clade comprising horseshoe crabs, Ricinulei, and Arachnopulmonata (scorpions, pseudoscorpions, and Tetrapulmonata).<ref>{{Cite journal |last1=Ballesteros |first1=Jesús A |last2=Sharma |first2=Prashant P |date=2019-11-01 |editor-last=Halanych |editor-first=Ken |title=A Critical Appraisal of the Placement of Xiphosura (Chelicerata) with Account of Known Sources of Phylogenetic Error |url=https://academic.oup.com/sysbio/article/68/6/896/5319972 |journal=Systematic Biology |language=en |volume=68 |issue=6 |pages=896–917 |doi=10.1093/sysbio/syz011 |pmid=30917194 |issn=1063-5157|doi-access=free }}</ref><ref>{{Cite journal |last1=Ballesteros |first1=Jesús A |last2=Santibáñez-López |first2=Carlos E |last3=Baker |first3=Caitlin M |last4=Benavides |first4=Ligia R |last5=Cunha |first5=Tauana J |last6=Gainett |first6=Guilherme |last7=Ontano |first7=Andrew Z |last8=Setton |first8=Emily V W |last9=Arango |first9=Claudia P |last10=Gavish-Regev |first10=Efrat |last11=Harvey |first11=Mark S |last12=Wheeler |first12=Ward C |last13=Hormiga |first13=Gustavo |last14=Giribet |first14=Gonzalo |last15=Sharma |first15=Prashant P |date=2022-02-03 |editor-last=Teeling |editor-first=Emma |title=Comprehensive Species Sampling and Sophisticated Algorithmic Approaches Refute the Monophyly of Arachnida |url=https://academic.oup.com/mbe/article/doi/10.1093/molbev/msac021/6522129 |journal=Molecular Biology and Evolution |language=en |volume=39 |issue=2 |doi=10.1093/molbev/msac021 |issn=0737-4038 |pmc=8845124 |pmid=35137183}}</ref> Although superficially similar to and often misidentified as [[spider]]s (order [[Araneae]]), the Opiliones are a distinct order that is not closely related to spiders. They can be easily distinguished from long-legged spiders by their fused body regions and single pair of eyes in the middle of the [[cephalothorax]]. Spiders have a distinct abdomen that is separated from the cephalothorax by a constriction, and they have three to four pairs of eyes, usually around the margins of the cephalothorax.

== Description ==
{{Main|Opiliones anatomy}}
[[File:Pseudo-araña nocturna (opilion).jpg|thumb|left|Chilean harvestman (''[[Pachyloidellus goliath]]'')]]
[[File:Harvester body close up.jpg|thumb|left|North European harvestman (''[[Leiobunum rotundum]]'') body]]
[[File:We-2012-09-09.ogv|thumb|250px|Harvestmen (Opiliones sp.) filmed in Hesse, Germany]]
The Opiliones are known for having exceptionally long legs relative to their body size; however, some species are short-legged. As in all Arachnida, the body in the Opiliones has two [[Tagma (biology)|tagmata]], the [[Anatomical terms of location|anterior]] [[cephalothorax]] or [[prosoma]], and the [[Anatomical terms of location|posterior]] 10-segmented [[abdomen]] or [[opisthosoma]]. The most easily discernible difference between harvestmen and spiders is that in harvestmen, the connection between the cephalothorax and abdomen is broad, so that the body appears to be a single [[oval]] structure. Other differences include the fact that Opiliones have no [[Spider Bite|venom]] glands in their [[chelicerae]] and thus pose no danger to humans.

They also have no silk glands and therefore do not build webs. In some highly derived species, the first five abdominal segments are fused into a [[Anatomical terms of location|dorsal]] shield called the [[scute|scutum]], which in most such species is fused with the [[carapace]]. Some such Opiliones only have this shield in the males. In some species, the two posterior abdominal segments are reduced. Some of them are divided [[Anatomical terms of location|medially]] on the surface to form two plates beside each other. The second pair of legs is longer than the others and function as [[Antenna (biology)|antennae]] or feelers. In short-legged species, this may not be obvious.

The feeding apparatus ([[stomotheca]]) differs from most arachnids in that Opiliones can swallow chunks of solid food, not only liquids. The stomotheca is formed by extensions of the coxae of the [[pedipalp]]s and the first pair of legs.

Most Opiliones, except for Cyphophthalmi, have long been thought to have a single pair of camera-type eyes in the middle of the head, oriented sideways. Eyes in Cyphophthalmi, when present, are located laterally, near the ozopores. A 305-million-year-old fossilized harvestman with two pairs of eyes was reported in 2014. This find suggested that the eyes in Cyphophthalmi are not homologous to the eyes of other harvestmen.<ref>{{Cite web |last=Blaszczak-Boxe |first=Agata |date=2014-04-10 |title=4-Eyed Daddy Longlegs Helps Explain Arachnid Evolution (Video) |url=https://www.livescience.com/44742-daddy-longlegs-fossil.html |access-date=2023-07-16 |website=livescience.com |language=en}}</ref><ref>{{cite journal |title=A Paleozoic Stem Group to Mite Harvestmen Revealed through Integration of Phylogenetics and Development |doi=10.1016/j.cub.2014.03.039 |pmid=24726154 |volume=24 |issue=9 |journal=Curr Biol |pages=1017–23 | last1 = Garwood | first1 = RJ | last2 = Sharma | first2 = PP | last3 = Dunlop | first3 = JA | last4 = Giribet | first4 = G|year=2014 |doi-access=free |bibcode=2014CBio...24.1017G }}</ref> Many cave-adapted species are eyeless, such as the Brazilian ''[[Caecobunus termitarum]]'' ([[Grassatores]]) from [[termite]] nests, ''[[Giupponia chagasi]]'' ([[Gonyleptidae]]) from caves, most species of Cyphophthalmi, and all species of the [[Guasiniidae]].<ref>{{cite journal |first1=Ricardo |last1=Pinto-da-Rocha |first2=Adriano B. |last2=Kury |year=2003 |title=Third species of Guasiniidae (Opiliones, Laniatores) with comments on familial relationships |journal=[[Journal of Arachnology]] |volume=31 |issue=3 |pages=394–399 |url=http://www.americanarachnology.org/JoA_free/JoA_v31_n3/arac-031-03-0394.pdf |doi=10.1636/H02-59 |s2cid=85918640 |access-date=2007-08-27 |archive-date=2016-03-28 |archive-url=https://web.archive.org/web/20160328120657/http://www.americanarachnology.org/JoA_free/JoA_v31_n3/arac-031-03-0394.pdf |url-status=dead }}</ref> However, recent work studying the embryonic development of the species ''[[Phalangium opilio]]'' and some Laniatores revealed that harvestman in addition to a pair of median eyes also have two sets of vestigial eyes: one median pair (homologous to those of [[horseshoe crab]]s and [[sea spider]]s), and one lateral pair (homologous to facetted eyes of horseshoe crabs and insects).<ref name=":17">{{Cite journal |last1=Gainett |first1=Guilherme |last2=Klementz |first2=Benjamin C. |last3=Blaszczyk |first3=Pola |last4=Setton |first4=Emily V.W. |last5=Murayama |first5=Gabriel P. |last6=Willemart |first6=Rodrigo |last7=Gavish-Regev |first7=Efrat |last8=Sharma |first8=Prashant P. |date=February 2024 |title=Vestigial organs alter fossil placements in an ancient group of terrestrial chelicerates |url=https://linkinghub.elsevier.com/retrieve/pii/S0960982224001532 |journal=Current Biology |volume=34 |issue=6 |pages=1258–1270.e5 |language=en |doi=10.1016/j.cub.2024.02.011|pmid=38401545 }}</ref> This discovery suggests that the neuroanatomy of harvestmen is more primitive than derived arachnid groups, like spiders and scorpions. It also showed that the four-eyed fossil harvestman previously discovered is most likely a member of the suborder [[Eupnoi]] (true daddy-longlegs).<ref name=":17" />

[[File:Harvestman macro.jpg|thumb|right|A harvestman (a male ''Phalangium opilio''), showing the almost fused arrangement of abdomen and cephalothorax that distinguishes these arachnids from [[spider]]s]]
Harvestmen have a pair of prosomatic defensive [[scent gland]]s ([[ozopore]]s) that secrete a peculiar-smelling fluid when disturbed. In some species, the fluid contains noxious [[1,4-Benzoquinone|quinones]]. They do not have [[book lungs]], and breathe through [[invertebrate trachea|tracheae]]. A pair of [[Spiracle (arthropods)|spiracles]] is located between the base of the fourth pair of legs and the abdomen, with one opening on each side. In more active species, spiracles are also found upon the [[tibia]] of the legs. They have a [[gonopore]] on the ventral cephalothorax, and the [[animal sexual behavior|copulation]] is direct as [[Opiliones penis|male Opiliones have a penis]], unlike other arachnids. All species lay [[Egg (biology)|eggs]].

Typical body length does not exceed {{convert|7|mm|abbr=on}}, and some species are smaller than 1&nbsp;mm, although the largest known species, ''[[Trogulus torosus]]'' ([[Trogulidae]]), grows as long as {{convert|22|mm|abbr=on}}.<ref name=pinto/> The leg span of many species is much greater than the body length and sometimes exceeds {{convert|160|mm|abbr=on}} and to {{convert|340|mm|abbr=on}} in Southeast Asia.<ref>{{Cite web |url=http://www.senckenberg.de/root/index.php?page_id=5210&year=2012&action=press&id=2480 |title=SENCKENBERG world of biodiversity &#124; About us &#124; Communications &#124; Newsroom |access-date=2015-05-29 |archive-url=https://web.archive.org/web/20151119111459/http://www.senckenberg.de/root/index.php?page_id=5210&year=2012&action=press&id=2480 |archive-date=2015-11-19 |url-status=dead }}</ref> Most species live for a year.

==Behavior==
[[File:Harvestman eating skink tail.jpg|thumb|left|Harvestman eating a [[skink]] tail]]
[[File:Harvestman Opiliones grooming 2016-05-15.jpg|thumb|left|''[[Protolophus]]'' sp. cleaning its legs]]
[[File:Opiliones.jpg|thumb|left|A male ''[[Phalangium opilio]]'', showing the long legs and the [[tarsomere]]s (the many small segments making up the end of each leg)]]
[[File:Parasitismus.jpg|thumb|right|[[Mite]]s parasitising a [[harvestman]]]]
[[File:Opiliones 20100626.jpg|thumb|right|Gregarious behavior in Opiliones]]

Many species are [[omnivorous]], eating primarily small [[insect]]s and all kinds of plant material and [[fungi]]. Some are [[scavenger]]s, feeding upon dead organisms, bird dung, and other [[Feces|fecal]] material. Such a broad range is unusual in arachnids, which are typically pure predators. Most hunting harvestmen ambush their prey, although active hunting is also found. Because their eyes cannot form images, they use their second pair of legs as antennae to explore their environment. Unlike most other arachnids, harvestmen do not have a sucking stomach or a filtering mechanism. Rather, they ingest small particles of their food, thus making them vulnerable to internal parasites such as [[gregarine]]s.<ref name=pinto/>

Although [[parthenogenesis|parthenogenetic]] species do occur, most harvestmen [[Sexual reproduction|reproduce sexually]]. Except from small [[fossorial]] species in the suborder Cyphophthalmi, where the males deposit a [[spermatophore]], [[mating]] involves direct copulation. The females store the sperm, which is aflagellate and immobile, at the tip of her ovipositor. The eggs are fertilized during oviposition.<ref>{{Cite book |last=Cowles |first=Jillian |url=https://books.google.com/books?id=3itLDwAAQBAJ&dq=Opiliones+sperm+tip+of+the+ovipositor+eggs&pg=PA106 |title=Amazing Arachnids |date=2018-06-12 |publisher=Princeton University Press |isbn=978-1-4008-9018-7 |language=en}}</ref> The males of some species offer a secretion (nuptial gift) from their chelicerae to the female before copulation. Sometimes, the male guards the female after copulation, and in many species, the males defend territories. In some species, males also exhibit post-copulatory behavior in which the male specifically seeks out and shakes the female's sensory leg. This is believed to entice the female into mating a second time.<ref>{{cite journal | last1 = Fowler-Finn | first1 = K.D. | last2 = Triana | first2 = E. | last3 = Miller | first3 = O.G. | s2cid = 49329266 | year = 2014 | title = Mating in the harvestman ''Lieobunum vittatum'' (Arachnida: Opiliones): from premating struggles to solicitous tactile engagement | journal = Behaviour | volume = 151 | issue = 12–13| pages = 1663–1686 | doi=10.1163/1568539x-00003209}}</ref>

The female lays her eggs shortly after mating to several months later. Some species build nests for this purpose. A unique feature of harvestmen is that some species practice parental care, in which the male is solely responsible for guarding the eggs resulting from multiple partners, often against [[Cannibalism (zoology)|egg-eating females]], and cleaning the eggs regularly.<ref>{{Cite journal|last1=Machado|first1=G.|last2=Raimundo|first2=R. L. G.|s2cid=18019589|date=2001|title=Parental investment and the evolution of subsocial behaviour in harvestmen (Arachnida: Opiliones)|journal=Ethology Ecology & Evolution|volume=13|issue=2|pages=133–150|doi=10.1080/08927014.2001.9522780|bibcode=2001EtEcE..13..133M }}</ref> [[Paternal care]] has evolved at least three times independently: once in the clade Progonyleptoidellinae + Caelopyginae, once in the Gonyleptinae, and once in the Heteropachylinae.<ref>{{cite journal | url=https://www.jstor.org/stable/40233818 | jstor=40233818 | title=Reproductive Behavior of Chavesincola inexpectabilis (Opiliones, Gonyleptidae) with Description of a New and Independently Evolved Case of Paternal Care in Harvestmen | last1=Nazareth | first1=Taís M. | last2=Machado | first2=Glauco | journal=The Journal of Arachnology | year=2009 | volume=37 | issue=2 | pages=127–134 | doi=10.1636/ST08-32.1 | s2cid=85846440 }}</ref> [[Parental care|Maternal care]] in opiliones probably evolved due to natural selection, while paternal care appears to be the result of sexual selection.<ref>{{Cite journal |last1=Machado |first1=Glauco |last2=Requena |first2=Gustavo S. |last3=Buzatto |first3=Bruno A. |date=2009-12-06 |title=Reproductive Behavior in Harvestman (Arachnida): Mating Systems and Parental Care |url=https://revistas.ufrj.br/index.php/oa/article/view/7063 |journal=Oecologia Australis |language=en-US |volume=13 |issue=1 |pages=58–79 |doi=10.4257/oeco.2009.1301.05 |issn=2177-6199|doi-access=free }}</ref> Depending on circumstances such as temperature, the eggs may hatch at any time after the first 20 days, up to about half a year after being laid. Harvestmen variously pass through four to eight nymphal [[instar]]s to reach maturity, with most known species having six instars.<ref name=pinto/>

Most species are [[nocturnal]] and colored in hues of brown, although a number of [[diurnal animal|diurnal]] species are known, some of which have vivid patterns in yellow, green, and black with varied reddish and blackish mottling and reticulation.

Many species of harvestmen easily tolerate members of their own species, with aggregations of many individuals often found at protected sites near water. These aggregations may number 200 individuals in the [[Laniatores]], and more than 70,000 in certain [[Eupnoi]]. [[Wiktionary:gregarious#Adjective|Gregarious]] behavior is likely a strategy against climatic odds, but also against predators, combining the effect of scent secretions, and reducing the probability of any particular individual being eaten.<ref name="pinto" />

Harvestmen clean their legs after eating by drawing each leg in turn through their jaws.

== Antipredator defences ==
Predators of harvestmen include a variety of animals, including some mammals,<ref>{{Cite journal|last=Cáceres|first=N.C.|date=2002|title=Food Habits and Seed Dispersal by the White-Eared Opossum, Didelphis albiventris, in Southern Brazil.|journal= Studies on Neotropical Fauna and Environment|volume=37|issue=2|pages=97–104|doi=10.1076/snfe.37.2.97.8582|bibcode=2002SNFE...37...97C |s2cid=85961182}}</ref><ref>{{Cite journal|last1=Cáceres|first1=N.C.|last2=Monteiro-Filho|first2=E.L.A|date=2001|title=Food Habits, Home Range and Activity of Didelphis aurita (Mammalia, Marsupialia) in a Forest Fragment of Southern Brazil.|journal= Studies on Neotropical Fauna and Environment|volume=36|issue=2|pages=85–92|doi=10.1076/snfe.36.2.85.2138|bibcode=2001SNFE...36...85C |s2cid=83850344}}</ref> amphibians, and other arachnids like spiders<ref name=":0">{{Cite journal|last1=da Silva Souza|first1=E.|last2=Willemart|first2=R.H.|date=2011|title=Harvest-ironman: heavy armature and not its defensive secretions, protects a harvestman against a spider.|journal=Anim. Behav.|volume=81|pages=127–133|doi=10.1016/j.anbehav.2010.09.023|s2cid=54254258}}</ref><ref name=":1">{{Cite journal|last1=Willemart|first1=R.H.|last2=Pellegatti-Franco|first2=F.|date=2006|title=The spider Enoploctenus cyclothorax (Araneae, Ctenidae) avoids preying on the harvestman Mischonyx cuspidatus (Opiliones, Gonyleptidae).|journal=J. Arachnol.|volume=34|issue=3|pages=649–652|doi=10.1636/S05-70.1|s2cid=85621336|url=https://www.biodiversitylibrary.org/part/228985}}</ref> and scorpions.<ref name=":2">{{cite journal |last1=Albín |first1=A. |last2=Toscano-Gadea |first2=C. A. |year=2015 |title=Predation among armored arachnids: Bothriurus bonariensis (Scorpions, Bothriuridae) versus four species of harvestmen (Harvestmen, Gonyleptidae) |journal=Behav. Processes |volume=121 |issue= |pages=1–7 |doi=10.1016/j.beproc.2015.10.003 |pmid=26470886 |s2cid=1994257 }}</ref> Opiliones display a variety of primary and secondary defences against predation,<ref>{{cite book |last=Edmunds |first=M. |year=1974 |title=Defence in Animals : a Survey of Anti-predator Defences |location=New York |publisher=Longman |isbn=0-582-44132-3 }}</ref> ranging from morphological traits such as body armour to behavioral responses to chemical secretions.<ref>{{Cite journal |doi = 10.1093/beheco/ari075|title = Determining the fitness consequences of antipredation behavior|journal = Behavioral Ecology|volume = 16|issue = 5|pages = 945–956|year = 2005|last1 = Lind|first1 = Johan|last2 = Cresswell|first2 = Will|doi-access = free}}</ref><ref name=":3">{{Cite journal |doi = 10.1007/s10886-005-7611-0|pmid = 16273426|title = Chemical Defence in Harvestmen (Arachnida, Opiliones): Do Benzoquinone Secretions Deter Invertebrate and Vertebrate Predators?|journal = Journal of Chemical Ecology|volume = 31|issue = 11|pages = 2519–2539|year = 2005|last1 = Machado|first1 = Glauco|last2 = Carrera|first2 = Patricia C.|last3 = Pomini|first3 = Armando M.|last4 = Marsaioli|first4 = Anita J.| bibcode=2005JCEco..31.2519M |citeseerx = 10.1.1.384.1362|s2cid = 10906916}}</ref> Some of these defences have been attributed and restricted to specific groups of harvestmen.<ref name=":4">{{cite book |last1=Gnaspini |first1=P. |last2=Hara |first2=M. R. |year=2007 |chapter=Defense mechanisms |title=Harvestmen: The Biology of Opiliones |publisher=Harvard University Press |location=Cambridge, MA |pages=374–399 |isbn=978-0-674-02343-7 }}</ref>

=== Primary defences ===
Primary defences help the harvestmen avoid encountering a potential predator and include [[crypsis]], [[aposematism]], and [[mimicry]].

==== Crypsis ====
Particular patterns or colour markings on harvestmen's bodies can reduce detection by disrupting the animals' outlines or providing camouflage. Markings on legs can cause an interruption of the leg outline and loss of leg proportion recognition.<ref>Cokendolpher pers. comm.</ref> Darker colourations and patterns function as [[camouflage]] when they remain motionless.<ref name=":5">Gnaspini, P., Cavalheiro, A.J., 1998. Chemical and Behavioral Defensces of a Neotropical Cavernicolous Harvestman: Goniosoma spelaeum (Opiliones, Laniatores, Gonyleptidae). J. Arachnol. 26, 81–90.</ref> Within the genus ''[[Leiobunum]]'' are multiple species with cryptic colouration that changes over ontogeny to match the [[Habitat|microhabitat]] used at each life stage.<ref name=":4" /><ref>Edgar, A.L., 1971. Studies on the biology and ecology of Michigan Phalangida (Opiliones).</ref> Many species have also been able to camouflage their bodies by covering with secretions and debris from the [[leaf litter]] found in their environments.<ref name=":4" /><ref>{{Cite journal |last1=Leandro Firmo |first1=Carlos |last2=Pinto-da-Rocha |first2=Ricardo |date=2002 |title=A new species of pseudotrogulus roewer and assignment of the genus to the hernandariinae (opiliones, gonyleptidae) |url=http://dx.doi.org/10.1636/0161-8202(2002)030[0173:ansopr]2.0.co;2 |journal=Journal of Arachnology |volume=30 |issue=1 |pages=173 |doi=10.1636/0161-8202(2002)030[0173:ansopr]2.0.co;2 |s2cid=85822815 |issn=0161-8202}}</ref> Some hard-bodied harvestmen have [[Epibiont|epizoic]] [[cyanobacteria]] and [[Marchantiophyta|liverworts]] growing on their bodies that suggest potential benefits for camouflage against large backgrounds to avoid detection by [[Diurnality|diurnal]] predators.<ref>Machado, G., Vital, D.M., 2001. On the Occurrence of Epizoic Cyanobacteria and Liverworts on a Neotropical Harvestman (Arachnida: Opiliones) | BIOTROPICA</ref><ref>{{Cite journal |last1=Proud |first1=Daniel N. |last2=Wade |first2=Ryan R. |last3=Rock |first3=Philip |last4=Townsend |first4=Victor R. |last5=Chavez |first5=Donald Jiménez |date=August 2012 |title=Epizoic cyanobacteria associated with a Neotropical harvestman (Opiliones: Sclerosomatidae) from Costa Rica |url=http://dx.doi.org/10.1636/b11-24.1 |journal=Journal of Arachnology |volume=40 |issue=2 |pages=259–261 |doi=10.1636/b11-24.1 |s2cid=83994309 |issn=0161-8202}}</ref>

==== Aposematism and mimicry ====
Some harvestmen have elaborate and brightly coloured patterns or appendages which contrast with the body colouration, potentially serving as an aposematic warning to potential predators.<ref name=":4" /><ref name=":6">{{Cite journal |last1=González |first1=Andrés |last2=Rossini |first2=Carmen |last3=Eisner |first3=Thomas |date=2004-03-01 |title=Mimicry: imitative depiction of discharged defensive secretion on carapace of an opilionid |url=http://dx.doi.org/10.1007/s00049-003-0252-2 |journal=Chemoecology |volume=14 |issue=1 |pages=5–7 |doi=10.1007/s00049-003-0252-2 |bibcode=2004Checo..14....5G |s2cid=31558441 |issn=0937-7409|url-access=subscription }}</ref><ref name=":7">Pomini, A.M., Machado, G., Pinto-da-Rocha, R., Macías-Ordóñez, R., Marsaioli, A.J., 2010. Lines of defence in the harvestman Hoplobunus mexicanus (Arachnida: Opiliones): Aposematism, stridulation, thanatosis and irritant chemicals. Biochem. Syst. Ecol. 38, 300–308.</ref> This mechanism is thought to be commonly used during daylight, when they could be easily seen by any predators.

Other harvestmen may exhibit mimicry to resemble other species' appearances. Some Gonyleptidae individuals that produce [[Transparency and translucency|translucid]] secretions have orange markings on their [[carapace]]s. This may have an aposematic role by mimicking the colouration of glandular emissions of two other quinone-producing species.<ref name=":6" /> Mimicry ([[Müllerian mimicry]]) occurring between Brazilian harvestmen that resemble others could be explained by [[convergent evolution]].<ref name=":4" />

=== Secondary defences ===
Secondary defences allow for harvestmen to escape and survive from a predator after direct or indirect contact, including [[Apparent death|thanatosis]], [[Freezing behavior|freezing]], bobbing, [[autotomy]], fleeing, [[stridulation]], [[retaliation]] and chemical secretions.

==== Thanatosis ====
Some animals respond to attacks by simulating an apparent death to avoid either detection or further attacks.<ref>Humphreys, R.K., Ruxton, G.D., 2018. A review of thanatosis (death feigning) as an anti-predator behaviour. Behav. Ecol. Sociobiol. 72, 22.</ref> Arachnids such as spiders practise this mechanism when threatened or even to avoid being eaten by female spiders after mating.<ref>Hansen, L.S., Gonzales, S.F., Toft, S., Bilde, T., 2008. Thanatosis as an adaptive male mating strategy in the nuptial gift–giving spider Pisaura mirabilis. Behav. Ecol. 19, 546–551.</ref><ref>Jones, T.C., Akoury, T.S., Hauser, C.K., Moore, D., 2011. Evidence of circadian rhythm in antipredator behaviour in the orb-weaving spider Larinioides cornutus. Anim. Behav. 82, 549–555.</ref> Thanatosis is used as a second line of defence when detected by a potential predator and is commonly observed within the [[Dyspnoi]] and [[Laniatores]] suborders,<ref name=":7" /> with individuals becoming rigid with legs either retracted or stretched.<ref>Cokendolpher, J.C., 1987. Observations on the defensive behavior of a Neotropical Gonyleptidae (Arachnida, Opiliones). Revue Arachnologique, 7, pp.59–63.</ref><ref name=":8">Eisner, T., Alsop, D., Meinwald, J., 1978. Secretions of Opilionids, Whip Scorpions and Pseudoscorpions, in: Arthropod Venoms, Handbook of Experimental Pharmacology / Handbuch Der Experimentellen Pharmakologie. Springer, Berlin, Heidelberg, pp. 87–99.</ref><ref name=":9">Machado, G., Pomini, A.M., 2008. Chemical and behavioral defences of the neotropical harvestman Camarana flavipalpi (Arachnida: Opiliones). Biochem. Syst. Ecol. 36, 369–376.</ref><ref>Pereira, W., Elpino-Campos, A., Del-Claro, K., Machado, G., 2004. Behavioral repertory of the neotropical harvestman ilhaia cuspidata (opiliones, gonyleptidae). J. Arachnol. 32, 22–30.</ref>

==== Freezing ====
Freezing – or the complete halt of movement – has been documented in the family Sclerosomatidae.<ref>Misslin, R., 2003. The defence system of fear: behaviour and neurocircuitry. Neurophysiol. Clin. Neurophysiol. 33, 55–66.</ref> While this can mean an increased likelihood of immediate survival, it also leads to reduced food and water intake.<ref name=":10">Chelini, M.-C., Willemart, R.H., Hebets, E.A., 2009. Costs and benefits of freezing behaviour in the harvestman Eumesosoma roeweri (Arachnida, Opiliones). Behav. Processes 82, 153–159.</ref>

==== Bobbing ====
To deflect attacks and enhance escape, long-legged species – commonly known as daddy long-legs – from the [[Eupnoi]] suborder, use two mechanisms. One is bobbing, for which these particular individuals bounce their bodies. It potentially serves to confuse and deflect any identification of the exact location of their bodies.<ref name=":4" /><ref name=":10" /><ref>Field, L.H., Glasgow, S., 2001. The Biology of Wetas, King Crickets and Their Allies. CABI</ref><ref>Holmberg, R.G., Angerilli, N.P.D., LaCasse, L.J., 1984. Overwintering Aggregations of Leiobunum paessleri in Caves and Mines (Arachnida, Opiliones). J. Arachnol. 12, 195–204.</ref> This can be a deceiving mechanism to avoid predation when they are in a large aggregation of individuals, which are all trembling at the same time.<ref name=":4" /><ref name=":11">Escalante, I., Albín, A., Aisenberg, A., 2013. Lacking sensory (rather than locomotive) legs affects locomotion but not food detection in the harvestman Holmbergiana weyenberghi. Can. J. Zool. 91, 726–731.</ref> Cellar spiders ([[Pholcidae]]) that are commonly mistaken for daddy long-legs (Opiliones) also exhibit this behavior when their webs are disturbed or even during courtship.<ref>Huber, B.A., Eberhard, W.G., 1997. Courtship, copulation, and genital mechanics in Physocyclus globosus (Araneae, Pholcidae). Can. J. Zool. 75, 905–918.</ref>

==== Autotomy ====
[[File:Rilaena triangularis 269725984.jpg|thumb|''[[Rilaena triangularis]]'' with several missing legs]]
Autotomy is the voluntary amputation of an appendage and is employed to escape when restrained by a predator.<ref>Domínguez, M., Escalante, I., Carrasco-Rueda, F., Figuerola-Hernández, C.E., Marta Ayup, M., Umaña, M.N., Ramos, D., González-Zamora, A., Brizuela, C., Delgado, W., Pacheco-Esquivel, J., 2016. Losing legs and walking hard: effects of autotomy and different substrates in the locomotion of harvestmen in the genus Prionostemma. J. Arachnol. 44, 76–82.</ref><ref>Fleming, P.A., Muller, D., Bateman, P.W., 2007. Leave it all behind: a taxonomic perspective of autotomy in invertebrates. Biological Reviews.</ref><ref name=":12">Roth, V.D., Roth, B.M., 1984. review of appendotomy in spiders and other arachnids. Bull.-Br. Arachnol. Soc.</ref><ref>Mattoni, C.I., García Hernández, S., Botero-Trujillo, R., Ochoa, J.A., Ojanguren-Affilastro, A.A., Outeda-Jorge, S., Pinto-da-Rocha, R. and Yamaguti, H.Y., 2001. Perder la cola o la vida. In ''Primer caso de autotomía en escorpiones (Scorpiones: Buthidae). III Congreso Latinoamericano de Aracnología, Memorias y Resúmenes'' (pp. 83–84).</ref> Eupnoi individuals, more specifically sclerosomatid harvestmen, commonly use this strategy in response to being captured.<ref name=":11" /><ref name=":13">Houghton, J.E., Townsend, V.R., Proud, D.N., 2011. The Ecological Significance of Leg Autotomy for Climbing Temperate Species of Harvestmen (Arachnida, Opiliones, Sclerosomatidae). Southeast. Nat. 10, 579–590.</ref><ref name=":14">Guffey, C., 1998. Leg Autotomy and Its Potential Fitness Costs for Two Species of Harvestmen (Arachnida, Opiliones). J. Arachnol. 26, 296–302.</ref> This strategy can be costly because harvestmen do not regenerate their legs,<ref name=":4" /> and leg loss reduces locomotion, speed, climbing ability, sensory perception, food detection, and territoriality.<ref name=":11" /><ref name=":14" /><ref name=":13" /><ref>Macias-Ordonez, R., 1998. The mating system of Leiobunum vittatum Say 1821 (Arachnida: Opiliones: Palpatores): Resource defense polygyny in the striped harvestman.</ref>

Autotomised legs provide a further defence from predators because they can twitch for 60 seconds to an hour after detachment.<ref name=":12" /> This can also potentially serve as deflection from an attack and deceive a predator from attacking the animal. It has been shown to be successful against ants and spiders.<ref name=":8" />

The legs continue to twitch after they are detached because 'pacemakers' are located in the ends of the first long segment (femur) of their legs. These pacemakers send signals via the nerves to the muscles to extend the leg and then the leg relaxes between signals. While some harvestman's legs twitch for a minute, others have been recorded to twitch up to an hour. The twitching has been hypothesised to function as an evolutionary advantage by keeping the attention of a predator while the harvestman escapes.<ref name=pinto/>

==== Fleeing ====
Individuals that are able to detect potential threats can flee rapidly from attack. This is seen with multiple long-legged species in the [[Leiobunum]] clade that either drop and run, or drop and remain motionless.<ref>Machado, G., Raimundo, R.L.G., Oliveira, P.S., 2000. Daily activity schedule, gregariousness, and defensive behaviour in the Neotropical harvestman Goniosoma longipes (Opiliones: Gonyleptidae): Journal of Natural History: Vol 34, No 4.</ref> This is also seen when disturbing an aggregation of multiple individuals, where they all scatter.<ref name=":4" /><ref name=":11" />

==== Stridulation ====
Multiple species within the Laniatores and Dyspnoi possess [[stridulation|stridulating]] organs, which are used as [[Animal communication|intraspecific communication]] and have also been shown to be used as a second line of defense when restrained by a predator.<ref name=":7" />

==== Retaliation ====
Armored harvestmen in Laniatores can often use their modified morphology as weapons.<ref name=":0" /><ref name=":15">Dias, B.C., Willemart, R.H., 2013. The effectiveness of post-contact defenses in a prey with no pre-contact detection. Zoology 116, 168–174.</ref><ref name=":16">Segovia, J.M.G., Del-Claro, K., Willemart, R.H., 2015. Defences of a Neotropical harvestman against different levels of threat by the recluse spider. Behaviour 152, 757–773.</ref> Many have spines on their pedipalps, back legs, or bodies.<ref name=":4" /><ref>Eisner, T., Eisner, M., Siegler, M., 2005. Secret Weapons: Defenses of Insects, Spiders, Scorpions, and Other Many-legged Creatures. Harvard University Press.</ref> By pinching with their chelicerae and pedipalps, they can cause harm to a potential predator.<ref name=":0" /> Also this has been proven to increase survival against recluse spiders by causing injury, allowing the harvestman to escape from predation.<ref name=":16" />

==== Chemical ====
Harvestmen are well known for being chemically protected. They exude strongly odored secretions from their scent glands, called [[ozopore]]s,<ref name=":4" /><ref name=":5" /><ref name=":6" /><ref name=":9" /><ref>Shultz, J.W., Pinto-da-Rocha, R., 2007. Morphology and functional anatomy. Harvest. Biol. Opiliones Harv. Univ. Press Camb. Mass. Lond. Engl. 14–61.</ref> that act as a shield against predators; this creates a strong and unpleasant taste, which is often their most effective defense.<ref name=":15" /> In ''Cyphophthalmi'' the scent glands release [[naphthoquinones]], chloro-naphthoquinones and aliphatic [[methyl ketone]]s, ''Insidiatores'' use nitrogen-containing substances, [[terpenes]], [[aliphatic]] [[ketones]], and [[Phenols|phenolics]], while ''Grassatores'' use [[alkylated]] phenolics and [[benzoquinones]], and ''[[Palpatores]]'' use substances like naphthoquinones, methyl- and ethyl-ketones.<ref>[https://pubs.acs.org/doi/10.1021/acs.jnatprod.0c00277 A Novel Class of Defensive Compounds in Harvestmen: Hydroxy-γ-Lactones from the Phalangiid Egaenus convexus]</ref> These secretions have successfully protected the harvestmen against wandering spiders ([[Wandering spider|Ctenidae]]),<ref name=":0" /><ref name=":1" /> wolf spiders ([[Lycosidae]]) and ''[[Formica exsectoides]]'' ants.<ref name=":3" /> However, these chemical irritants are not able to prevent four species of harvestmen being preyed upon by the black scorpion ''[[Bothriurus]] bonariensis'' ([[Bothriuridae]]).<ref name=":2" /> These secretions contain multiple volatile compounds that vary among individuals and clades.<ref>Gnaspini, P., Rodrigues, G.S., 2011. Comparative study of the morphology of the gland opening area among Grassatores harvestmen (Arachnida, Opiliones, Laniatores)of Zoological Systematics and Evolutionary Research.</ref><ref>Hara, M. R., Gnaspini, P., 2003. Comparative study of the defensive behavior and morphology of the gland opening area among harvestmen (Arachnida, Opiliones, Gonyleptidae) under a phylogenetic perspective.</ref><ref>Shear, W. A., Jones, T. H., Guidry, H. M., Derkarabetian, S., Richart, C. H., Minor, M., Lewis, J. J., 2014. Chemical defenses in the opilionid infraorder Insidiatores: divergence in chemical defenses between Triaenonychidae and Travunioidea and within travunioid harvestmen (Opiliones) from eastern and western North America | Journal of Arachnology.</ref>

==Endangered status==
All [[troglobitic]] species (of all animal taxa) are considered to be at least threatened in [[Brazil]]. Four species of Opiliones are on the Brazilian national list of endangered species, all of them cave-dwelling: ''[[Giupponia chagasi]]'', ''Iandumoema uai'', ''Pachylospeleus strinatii'' and ''Spaeleoleptes spaeleus''.

Several Opiliones in Argentina appear to be vulnerable, if not endangered. These include ''Pachyloidellus fulvigranulatus'', which is found only on top of [[Cerro Uritorco]], the highest peak in the Sierras Chicas chain (provincia de Cordoba) and ''Pachyloides borellii'' is in rainforest patches in northwest Argentina which are in an area being dramatically destroyed by humans. The cave-living ''Picunchenops spelaeus'' is apparently endangered through human action. So far, no harvestman has been included in any kind of a Red List in Argentina, so they receive no protection.

''Maiorerus randoi'' has only been found in one cave in the [[Canary Islands]]. It is included in the Catálogo Nacional de especies amenazadas (National catalog of threatened species) from the [[Spain|Spanish]] government.

''[[Texella reddelli]]'' and ''[[Texella reyesi]]'' are listed as endangered species in the United States. Both are from caves in central [[Texas]]. ''[[Texella cokendolpheri]]'' from a cave in central Texas and ''Calicina minor'', ''Microcina edgewoodensis'', ''Microcina homi'', ''Microcina jungi'', ''Microcina leei'', ''Microcina lumi'', and ''Microcina tiburona'' from around springs and other restricted habitats of central [[California]] are being considered for listing as endangered species, but as yet receive no protection.

==Misconception==
[[File:Harvestman Mouth.JPG|thumb|right|[[Chela (organ)|Chela]]te (pincer-like) chelicerae typical of harvestmen (200× magnification); these chelicerae are homologous to chelicerae that take the form of fangs in spiders or [[Chela (organ)|chela]]e in the [[Solifugae]].

[[File:Opiliones chelicerae photo.jpg|center|frameless|207x207px]]''Opilio canestrinii'' chelicerae shown in context to the rest of the body.]]

An [[urban legend]] claims that the harvestman is the most [[venom]]ous animal in the world;<ref name="Berenbaum2009">{{cite book |last=Berenbaum |first=May R. |title=The Earwig's Tail: a modern bestiary of multi-legged legends|url=https://books.google.com/books?id=JsB9YTivZVAC&pg=PA143|date=30 September 2009|publisher=Harvard University Press|isbn=978-0-674-05356-4|page=143}}</ref> however, it possesses fangs too short or a mouth too round and small to bite a human, rendering it harmless (the same myth applies to ''[[Pholcus phalangioides]]'' and the [[Tipuloidea|crane fly]], which are both also called a "daddy longlegs").<ref>The Spider Myths Site: [http://www.washington.edu/burkemuseum/spidermyth/myths/daddyvenom.html "Daddy-Longlegs"] {{Webarchive|url=https://web.archive.org/web/20070714061900/http://www.washington.edu/burkemuseum/spidermyth/myths/daddyvenom.html |date=2007-07-14 }}</ref> None of the known species of harvestmen have venom glands; their [[chelicerae]] are not hollowed fangs but grasping claws that are typically very small and not strong enough to break human skin.

==Research==
Harvestmen are a scientifically neglected group. Description of new taxa has always been dependent on the activity of a few dedicated taxonomists. [[Carl Friedrich Roewer]] described about a third (2,260) of today's known species from the 1910s to the 1950s, and published the landmark systematic work {{lang|de|Die Weberknechte der Erde}} (Harvestmen of the World) in 1923, with descriptions of all species known to that time. Other important taxonomists in this field include:

*[[Pierre André Latreille]] (18th century)
*[[Carl Ludwig Koch]], [[Maximilian Perty]] (1830s–1850s)
*[[L. Koch]], [[Tord Tamerlan Teodor Thorell]] (1860s–1870s)
*[[Eugène Simon]], William Sørensen (1880s–1890s)
*James C. Cokendolpher, Raymond Forster, [[Clarence J. Goodnight|Clarence and Marie Goodnight]], Jürgen Gruber, [[Reginald Frederick Lawrence]], Jochen Martens, [[Cândido Firmino de Mello-Leitão]] (20th century)
*[[Gonzalo Giribet]], Adriano Brilhante Kury, Tone Novak (21st century)

Since the 1990s, study of the biology and ecology of harvestmen has intensified, especially in [[South America]].<ref name=pinto/>

Early work on the developmental biology of Opiliones from the mid-20th century was resurrected by [[Prashant P. Sharma]], who established ''[[Phalangium opilio]]'' as a model system for the study of arachnid comparative genomics and [[Evolutionary developmental biology|evolutionary-developmental biology]].

==Phylogeny==
{{Main|Harvestman phylogeny}}
Harvestmen are ancient [[arachnid]]s. Fossils from the [[Devonian]] [[Rhynie chert]], 410 million years ago, already show characteristics like tracheae and sexual organs, indicating that the group has lived on land since that time. Despite being similar in appearance to, and often confused with, spiders, they are probably closely related to the [[scorpion]]s, [[pseudoscorpion]]s, and [[solifuge]]s; these four orders form the clade [[Dromopoda]]. The Opiliones have remained almost unchanged morphologically over a long period.<ref name=pinto/><ref name=Mont /> Indeed, one species discovered in China, ''Mesobunus martensi'', fossilized by fine-grained volcanic ash around 165 million years ago, is hardly discernible from modern-day harvestmen and has been placed in the extant family [[Sclerosomatidae]].<ref>{{cite magazine |last=Perkins |first=Sid |magazine=[[Science News]] |url=http://www.sciencenews.org/view/generic/id/44918/title/Long-lasting_daddy_longlegs |title=Long-lasting daddy longlegs |date=June 23, 2009}}</ref><ref name="Huang">{{cite journal |author=Diying Huang, Paul A. Selden & Jason A. Dunlop |year=2009 |title=Harvestmen (Arachnida: Opiliones) from the Middle Jurassic of China |journal=[[Naturwissenschaften]] |volume=96 |issue=8 |pages=955–962 |url=http://www.museunacional.ufrj.br/mndi/Aracnologia/pdfliteratura/Huang%20et%20al%20(2009)%20Jurassic%20harvestmen%20from%20China%202.pdf |pmid=19495718 |doi=10.1007/s00114-009-0556-3 |bibcode=2009NW.....96..955H |s2cid=9570512 |access-date=2012-12-21 |archive-date=2016-03-05 |archive-url=https://web.archive.org/web/20160305012108/http://www.museunacional.ufrj.br/mndi/Aracnologia/pdfliteratura/Huang%20et%20al%20(2009)%20Jurassic%20harvestmen%20from%20China%202.pdf |url-status=dead }}</ref>

==Systematics==
{{Main|Harvestman phylogeny}}
The interfamilial relationships within Opiliones are not yet fully resolved, although significant strides have been made in recent years to determine these relationships. The following list is a compilation of interfamilial relationships recovered from several recent phylogenetic studies, although the placement and even monophyly of several taxa are still in question.<ref>{{Cite journal|last1=Giribet|first1=Gonzalo|last2=Sharma|first2=Prashant P.|last3=Benavides|first3=Ligia R.|last4=Boyer|first4=Sarah L.|last5=Clouse|first5=Ronald M.|last6=De Bivort|first6=Benjamin L.|last7=Dimitrov|first7=Dimitar|last8=Kawauchi|first8=Gisele Y.|last9=Murienne|first9=Jerome|date=2012-01-01|title=Evolutionary and biogeographical history of an ancient and global group of arachnids (Arachnida: Opiliones: Cyphophthalmi) with a new taxonomic arrangement|journal=Biological Journal of the Linnean Society|language=en|volume=105|issue=1|pages=92–130|doi=10.1111/j.1095-8312.2011.01774.x|issn=1095-8312|doi-access=free}}</ref><ref>{{Cite journal|last1=Kury|first1=Adriano B.|last2=Villarreal M.|first2=Osvaldo|s2cid=84029705|date=2015-05-01|title=The prickly blade mapped: establishing homologies and a chaetotaxy for macrosetae of penis ventral plate in Gonyleptoidea (Arachnida, Opiliones, Laniatores)|journal=Zoological Journal of the Linnean Society|language=en|volume=174|issue=1|pages=1–46|doi=10.1111/zoj.12225|issn=1096-3642}}</ref><ref>Fernández R, Sharma PP, Tourinho AL, Giribet G. 2017 The Opiliones tree of life: shedding light on harvestmen relationships through transcriptomics. Proc. R. Soc. B 284: 20162340. https://dx.doi.org/10.1098/rspb.2016.2340</ref><ref>{{Cite journal|last1=Groh|first1=Selina|last2=Giribet|first2=Gonzalo|date=2015-06-01|title=Polyphyly of Caddoidea, reinstatement of the family Acropsopilionidae in Dyspnoi, and a revised classification system of Palpatores (Arachnida, Opiliones)|journal=Cladistics|language=en|volume=31|issue=3|pages=277–290|doi=10.1111/cla.12087|pmid=34772266 |s2cid=85408627|issn=1096-0031|doi-access=free}}</ref><ref>{{Cite journal|last1=Kury|first1=Adriano B.|last2=Mendes|first2=Amanda Cruz|last3=Souza|first3=Daniele R.|date=2014-11-05|title=World Checklist of Opiliones species (Arachnida). Part 1: Laniatores – Travunioidea and Triaenonychoidea|journal=Biodiversity Data Journal|volume=2|issue=2|pages=e4094|doi=10.3897/BDJ.2.e4094|issn=1314-2836|pmc=4238074|pmid=25425936 |doi-access=free }}</ref>

{{div col|colwidth=30em}}
* Suborder [[Cyphophthalmi]] <small>Simon, 1879</small> (about 200 species)
** Infraorder [[Boreophthalmi]] <small>Giribet, 2012</small>
*** Family [[Sironidae]] <small>Simon, 1879</small>
*** Family [[Stylocellidae]] <small>Hansen & Sørensen, 1904</small>
** Infraorder [[Scopulophthalmi]] <small>Giribet, 2012</small>
*** Family [[Pettalidae]] <small>Shear, 1980</small>
** Infraorder [[Sternophthalmi]] <small>Giribet, 2012</small>
*** Family [[Troglosironidae]] <small>Shear, 1993</small>
** Superfamily [[Ogoveoidea]] <small>Shear, 1980</small>
*** Family [[Neogoveidae]] <small>Shear, 1980</small>
*** Family [[Ogoveidae]] <small>Shear, 1980</small>
** Infraorder (indet).
*** Family [[Parasironidae]] <small>Karaman, Mitov & Snegovaya, 2024</small>
* Suborder [[Eupnoi]] <small>Hansen & Sørensen, 1904</small> (about 1,800 species)
** Superfamily [[Caddoidea]] <small>Banks, 1892</small>
*** Family [[Caddidae]] <small>Banks, 1892</small>
** Superfamily [[Phalangioidea]] <small>Latreille, 1802</small>
*** Family [[Globipedidae]] <small>Kury & Cokendolpher, 2020</small>
*** Family [[Neopilionidae]] <small>Lawrence, 1931</small>
*** Family [[Phalangiidae]] <small>Latreille, 1802</small>
*** Family [[Protolophidae]] <small>Banks, 1893</small>
*** Family [[Sclerosomatidae]] <small>Simon, 1879</small>
* Suborder [[Dyspnoi]] <small>Hansen & Sørensen, 1904</small> (about 400 species)
** Superfamily [[Acropsopilionoidea]] <small>Roewer, 1923</small>
*** Family [[Acropsopilionidae]] <small>Roewer, 1923</small>
** Superfamily [[Ischyropsalidoidea]] <small>Simon, 1879</small>
*** Family [[Ischyropsalididae]] <small>Simon, 1879</small>
*** Family [[Sabaconidae]] <small>Dresco, 1970</small>
*** Family [[Taracidae]] <small>Schönhofer, 2013</small>
** Superfamily [[Troguloidea]] <small>Sundevall, 1833</small>
*** Family [[Dicranolasmatidae]] <small>Simon, 1879</small>
*** Family [[Nemastomatidae]] <small>Simon, 1872</small>
*** Family [[Nipponopsalididae]] <small>Martens, 1976</small>
*** Family [[Trogulidae]] <small>Sundevall, 1833</small>
* Suborder [[Laniatores]] <small>Thorell, 1876</small> (about 4,200 species)
** Infraorder [[Insidiatores]] <small>Loman, 1900</small>
*** Superfamily [[Travunioidea]] <small>Absolon & Kratochvil, 1932</small>
**** Family [[Cladonychiidae]] <small>Hadži, 1935</small>
**** Family [[Cryptomastridae]] <small>Derkarabetian & Hedin, 2018</small>
**** Family [[Paranonychidae]] <small>Briggs, 1971</small>
**** Family [[Travuniidae]] <small>Absolon & Kratochvil, 1932</small>
*** Superfamily [[Triaenonychoidea]] <small>Sørensen, 1886</small>
**** Family [[Buemarinoidae]] <small>Karaman, 2019</small>
**** Family [[Lomanellidae]] <small>Mendes & Derkarabetian, 2021</small>
**** Family [[Synthetonychiidae]] <small>Forster, 1954</small>
**** Family [[Triaenonychidae]] <small>Sørensen, 1886</small>
** Infraorder [[Grassatores]] <small>Kury, 2002</small>
*** Superfamily [[Assamioidea]] <small>Sørensen, 1884</small>
**** Family [[Assamiidae]] <small>Sørensen, 1884</small>
**** Family [[Pyramidopidae]] <small>Sharma and Giribet, 2011</small>
**** Family [[Suthepiidae]] <small>Martens, 2020</small>
**** Family [[Trionyxellidae]] <small>Roewer, 1912</small>
*** Superfamily [[Epedanoidea]] <small>Sørensen, 1886</small>
**** Family [[Epedanidae]] <small>Sørensen, 1886</small>
**** Family [[Petrobunidae]] <small>Sharma and Giribet, 2011</small>
**** Family [[Podoctidae]] <small>Roewer, 1912</small>
**** Family [[Tithaeidae]] <small>Sharma and Giribet, 2011</small>
*** Superfamily [[Gonyleptoidea]] <small>Sundevall, 1833</small>
**** Family [[Agoristenidae]] <small>Šilhavý, 1973</small>
**** Family [[Ampycidae]] <small>Kury, 2003</small>
**** Family [[Askawachidae]] <small>Kury & Carvalho, 2020</small>
**** Family [[Cosmetidae]] <small>Koch, 1839</small>
**** Family [[Cranaidae]] <small>Roewer, 1913</small>
**** Family [[Cryptogeobiidae]] <small>Kury, 2014</small>
**** Family [[Gerdesiidae]] <small>Bragagnolo, 2015</small>
**** Family [[Gonyleptidae]] <small>Sundevall, 1833</small>
**** Family [[Manaosbiidae]] <small>Roewer, 1943</small>
**** Family [[Metasarcidae]] <small>Kury, 1994</small>
**** Family [[Nomoclastidae]] <small>Roewer, 1943</small>
**** Family [[Otilioleptidae]] <small>Acosta, 2019</small>
**** Family [[Prostygnidae]] <small>Roewer, 1913</small>
**** Family [[Stygnidae]] <small>Simon, 1879</small>
**** Family [[Stygnopsidae]] <small>Sørensen, 1932</small>
*** Superfamily [[Phalangodoidea]] <small>Simon, 1879</small>
**** Family [[Phalangodidae]] <small>Simon, 1879</small>
*** Superfamily [[Samooidea]] <small>Sørensen, 1886</small>
**** Family [[Biantidae]] <small>Thorell, 1889</small>
**** Family [[Samoidae]] <small>Sørensen, 1886</small>
**** Family [[Stygnommatidae]] <small>Roewer, 1923</small>
*** Superfamily [[Sandokanoidea]] <small>Özdikmen & Kury, 2007</small>
**** Family [[Sandokanidae]] <small>Özdikmen & Kury, 2007</small>
*** Superfamily [[Zalmoxoidea]] <small>Sørensen, 1886</small>
**** Family [[Escadabiidae]] <small>Kury & Pérez, 2003</small>
**** Family [[Fissiphalliidae]] <small>Martens, 1988</small>
**** Family [[Guasiniidae]] <small>Gonzalez-Sponga, 1997</small>
**** Family [[Icaleptidae]] <small>Kury & Pérez, 2002</small>
**** Family [[Kimulidae]] <small>Pérez González, Kury & Alonso-Zarazaga, 2007</small>
**** Family [[Zalmoxidae]] <small>Sørensen, 1886</small>
{{div col end}}

The family [[Stygophalangiidae]] (one species, ''[[Stygophalangium karamani]]'') from underground waters in [[North Macedonia]] is sometimes misplaced in the Phalangioidea. It is not a harvestman.

==Fossil record==
Despite their long history, few harvestman fossils are known. This is mainly due to their delicate body structure and terrestrial habitat, making them unlikely to be found in sediments. As a consequence, most known fossils have been preserved within [[amber]].

The oldest known harvestman, from the 410-million-year-old Devonian Rhynie chert, displayed almost all the characteristics of modern species, placing the origin of harvestmen in the [[Silurian]], or even earlier. A recent molecular study of Opiliones, however, dated the origin of the order at about 473 million years ago (Mya), during the Ordovician.<ref>{{Cite journal|last1=Sharma|first1=Prashant P.|last2=Giribet|first2=Gonzalo|date=2014|title=A revised dated phylogeny of the arachnid order Opiliones|journal=Frontiers in Genetics|language=en|volume=5|pages=255|doi=10.3389/fgene.2014.00255|pmid=25120562|pmc=4112917|issn=1664-8021|doi-access=free}}</ref>

No fossils of the [[Cyphophthalmi]] or [[Laniatores]] much older than 50 million years are known, despite the former presenting a [[basal clade]], and the latter having probably diverged from the Dyspnoi more than 300 Mya.

Naturally, most finds are from comparatively recent times. More than 20 fossil species are known from the [[Cenozoic]], three from the [[Mesozoic]],<ref name="Huang"/> and at least seven from the [[Paleozoic]].<ref>{{cite book |last=Dunlop |first=Jason A. |chapter=Paleontology |pages=247–265 |editor=Ricardo Pinto-da-Rocha, Glauco Machado & Gonzalo Giribet |title=Harvestmen: the Biology of Opiliones |year=2007 |publisher=[[Harvard University Press]] |isbn=978-0-674-02343-7}}</ref>

===Paleozoic===
The 410-million-year-old ''Eophalangium sheari'' is known from two specimens, one a female, the other a male. The female bears an [[ovipositor]] and is about {{convert|10|mm|abbr=on}} long, whilst the male had a discernable penis. Whether both specimens belong to the same species is not definitely known. They have long legs, [[Invertebrate trachea|tracheae]], and no median eyes. Together with the 305-million-year-old ''Hastocularis argus'', it forms the suborder [[Tetrophthalmi]], which was though to form the sister group to Cyphophthalmi.<ref name="Tetro">{{cite journal|title=A Paleozoic Stem Group to Mite Harvestmen Revealed through Integration of Phylogenetics and Development|first1=Russell J.|last1=Garwood|first2=Prashant P.|last2=Sharma|first3=Jason A.|last3=Dunlop|first4=Gonzalo|last4=Giribet|year=2014|journal=Current Biology|volume=24|issue=9|pages=1017–1023|doi=10.1016/j.cub.2014.03.039|pmid=24726154|doi-access=free|bibcode=2014CBio...24.1017G }}</ref><ref>{{cite news |last=Tepper |first=Fabien |title=Ancient four-eyed wonder resolves daddy longleg mystery|date=April 11, 2014|work=[[Christian Science Monitor]]|url=http://www.csmonitor.com/Science/2014/0411/Ancient-four-eyed-wonder-resolves-daddy-longleg-mystery|access-date=April 16, 2014}}</ref> However, recent reanalysis of harvestman phylogeny has shown that ''E. sheari'' and ''H. argus'' are in fact members of the suborder [[Eupnoi]], after it was discovered that living daddy-longlegs have the same arrangement of eyes as the fossils.<ref name=":17" />

''Brigantibunum listoni'' from East Kirkton near [[Edinburgh]] in Scotland is almost 340 million years old. Its placement is rather uncertain, apart from it being a harvestman.

From about 300 Mya, several finds are from the [[Coal Measures]] of North America and Europe.<ref name=Tetro /><ref name=Mont /> While the two described ''Nemastomoides'' species are currently grouped as Dyspnoi, they look more like Eupnoi.

''Kustarachne tenuipes'' was shown in 2004 to be a harvestman, after residing for almost one hundred years in its own arachnid order, the "Kustarachnida".

Some fossils from the [[Permian]] are possibly harvestmen, but these are not well preserved.

====Described species====
* ''[[Eophalangium sheari]]'' <small>Dunlop, 2004</small> (Tetrophthalmi) — [[Early Devonian]] ([[Rhynie chert|Rhynie]], [[Scotland]])
* ''[[Brigantibunum listoni]]'' <small>Dunlop, 2005</small> (Eupnoi?) — [[Early Carboniferous]] ([[East Kirkton]], Scotland)
* ''[[Echinopustulus samuelnelsoni]]'' <small>Dunlop, 2004</small> (Dyspnoi?) — [[Upper Carboniferous]] (Western [[Missouri]], U.S.)
* ''[[Eotrogulus fayoli]]'' <small>Thevenin, 1901</small> (Dyspnoi: † [[Eotrogulidae]]) — Upper Carboniferous ([[Commentry]], [[France]])
* ''[[Hastocularis argus]]'' <small>Garwood, 2014</small> (Tetrophthalmi) — Upper Carboniferous ([[Montceau-les-Mines]], France)
* ''[[Kustarachne longipes]]'' <small>(Petrunkevitch, 1913)</small> (Eupnoi) — Upper Carboniferous ([[Mazon Creek]], U.S.)
* ''[[Kustarachne tenuipes]]'' <small>Scudder, 1890</small> (Eupnoi) — Upper Carboniferous ([[Mazon Creek]], U.S.)
* ''[[Nemastomoides elaveris]]'' <small>Thevenin, 1901</small> (Dyspnoi: † [[Nemastomoididae]]) — Upper Carboniferous (Commentary, France)
* ''[[Nemastomoides longipes]]'' <small>Petrunkevitch, 1913</small> (Dyspnoi: † [[Nemastomoididae]]) — Upper Carboniferous (Mazon Creek, U.S.)

===Mesozoic===

* ''[[Burmalomanius circularis]]'' <small>Bartel et al, 2023 </small> (Podoctidae) — [[Myanmar]], [[Burmese amber]] (Cenomanian)
* ''[[Petroburma tarsomeria]]'' <small>Bartel et al, 2023 </small> (Petrobunidae) — [[Myanmar]], [[Burmese amber]] (Cenomanian)
* ''[[Mesodibunus tourinhoae]]'' <small>Bartel et al, 2023 </small> (Epedanidae) — [[Myanmar]], [[Burmese amber]] (Cenomanian)
* ''[[indet]]'' <small>Bartel et al, 2023 </small> (Insidiatores indet.) — [[Myanmar]], [[Burmese amber]] (Cenomanian)
etc. Bartel et al, 2023 report "These new records bring the total number of Burmese amber laniatorean species to ten"

* ''[[Halitherses grimaldii]]'', a long-legged Dyspnoi with large eyes, was found in [[Burmese amber]] dating from approximately 100 Mya. It has been suggested that this may be related to the Ortholasmatinae (Nemastomatidae).<ref>{{cite journal  |first1=Gonzalo |last1=Giribet |first2=Jason A. |last2=Dunlop |year=2005 |title=First identifiable Mesozoic harvestman (Opiliones: Dyspnoi) from Cretaceous Burmese amber |journal=[[Proceedings of the Royal Society B]] |volume=272 |issue=1567 |pages=1007–1013 |doi=10.1098/rspb.2005.3063 |pmid=16024358 |pmc=1599874}}</ref>

Currently, no fossil harvestmen are known from the [[Triassic]]. So far, they are also absent from the [[Lower Cretaceous]] [[Crato Formation]] of Brazil, a [[Lagerstätte]] that has yielded many other terrestrial arachnids. An unnamed long-legged harvestman was reported from the Early Cretaceous of [[Koonwarra]], [[Victoria (Australia)|Victoria]], Australia, which may be a Eupnoi.{{citation needed|date=April 2019}}

===Cenozoic===
Unless otherwise noted, all species are from the [[Eocene]].

* ''[[Trogulus]] [[Trogulus longipes|longipes]]'' <small>Haupt, 1956</small> (Dyspnoi: [[Trogulidae]]) — [[Geiseltal]], [[Germany]]
* ''[[Philacarus hispaniolensis]]'' <small></small> (Laniatores: [[Samoidae]]?) — [[Dominican amber]]
* ''[[Kimula]]'' species (Laniatores: [[Kimulidae]]) — Dominican amber
* ''[[Hummelinckiolus]] [[Hummelinckiolus silhavyi|silhavyi]]'' <small>Cokendolpher & Poinar, 1998</small> (Laniatores: Samoidae) — Dominican amber
* ''[[Caddo (harvestman)|Caddo]] [[Caddo dentipalpis|dentipalpis]]'' <small></small> (Eupnoi: [[Caddidae]]) — [[Baltic amber]]
* ''[[Dicranopalpus]] [[Dicranopalpus ramiger|ramiger]]'' <small>(Koch & Berendt, 1854)</small> (Eupnoi: [[Phalangiidae]]) — Baltic amber
* ''[[Opilio]] [[Opilio ovalis|ovalis]]'' <small></small> (Eupnoi: Phalangiidae?) — Baltic amber
* ''[[Cheiromachus coriaceus]]'' <small>Menge, 1854</small> (Eupnoi: Phalangiidae?) — Baltic amber
* ''[[Leiobunum]] [[Leiobunum longipes|longipes]]'' <small></small> (Eupnoi: [[Sclerosomatidae]]) — Baltic amber
* ''[[Histricostoma]] [[Histricostoma tuberculatum|tuberculatum]]'' <small></small> (Dyspnoi: [[Nemastomatidae]]) — Baltic amber
* ''[[Mitostoma]] [[Mitostoma denticulatum|denticulatum]]'' <small></small> (Dyspnoi: Nemastomatidae) — Baltic amber
* ''[[Nemastoma (harvestman)|Nemastoma]] [[Nemastoma incertum|incertum]]'' <small></small> (Dyspnoi: Nemastomatidae) — Baltic amber
* ''[[Sabacon]] [[Sabacon claviger|claviger]]'' <small></small> (Dyspnoi: [[Sabaconidae]]) — Baltic amber
* ''[[Petrunkevitchiana oculata]]'' <small>(Petrunkevitch, 1922)</small> (Eupnoi: [[Phalangioidea]]) — [[Florissant Fossil Beds National Monument]], USA ([[Oligocene]])
* ''[[Proholoscotolemon nemastomoides]]'' <small></small> (Laniatores: [[Cladonychiidae]]) — Baltic amber
* ''[[Siro platypedibus]]'' <small></small> (Cyphophthalmi: [[Sironidae]]) — Bitterfeld amber
* ''[[Amauropilio atavus]]'' <small>(Cockerell, 1907)</small> (Eupnoi: Sclerosomatidae) — Florissant, USA (Oligocene)
* ''[[Amauropilio lacoei]]'' (''A. lawei''?) <small>(Petrunkevitch, 1922)</small> — Florissant, USA (Oligocene)
* ''[[Pellobunus]] [[Pellobunus proavus|proavus]]'' <small>Cokendolpher, 1987</small> (Laniatores: Samoidae) — Dominican amber
* ''[[Phalangium]]'' species (Eupnoi: Phalangiidae) — near [[Rome]], [[Italy]] ([[Quaternary]])

== Etymology ==
{{wikt|Opiliones|harvestman}}
The Swedish naturalist and arachnologist [[Carl Jakob Sundevall]] (1801–1875) honored the naturalist [[Martin Lister]] (1638–1712) by adopting Lister's term {{wikt-lang|mul|Opiliones}} for this order, from Latin {{wikt-lang|la|ōpiliō}} (“shepherd”), because these arachnids were known in Lister's days as "{{wikt-lang|en|shepherd spider|shepherd spiders|i=-}}"; Lister characterized three species from England (although not formally describing them, being a [[Linnaean taxonomy|pre-Linnaean]] work).<ref>''Martin Lister's English Spiders, 1678''. Ed. John Parker and Basil Hartley (1992). Colchester, Essex: Harley Books. pp. 26 & 30. (Translation of the Latin original, ''Tractatus de Araneis''.)</ref>

In England, the Opiliones are often called "{{wikt-lang|en|harvestman|harvestmen|i=-}}" or "{{wikt-lang|en|harvest spider|harvest spiders|i=-}}". [[Folk etymology|Folk-etymological]] explanations for this are numerous, such as that they appear during [[harvest]] season, or because of a superstitious belief that if one is killed there will be a bad harvest that year,<ref>Frank Cowan, ''Curious Facts in the History of Insects'', p.321</ref> but these are unfounded. More likely, as in other European languages which call them a word meaning "cutter" or "scyther", the original explanation is that their oddly shaped legs look like tiny [[sickle]]s or [[scythe]]s.{{cn|date=February 2025}} The alternative name "shepherd spiders" is sometimes attributed to the assumption that Englishmen knew of the shepherds in the [[Landes (department)|Landes]] region of France who traditionally used [[stilts]] to better observe their wandering flocks from a distance, and so were reminded of them by the long-legged arachnid,<ref name="Corporation">{{citation|editor=Joyce Tavolacci|title=Insects and spiders of the world|url=https://books.google.com/books?id=_W1YlDF8cNsC&pg=PA263|volume=5: Harvester ant to leaf-cutting ant|year=2003|publisher=Marshall Cavendish|isbn=978-0-7614-7334-3|page=263}}</ref> but is much more likely just an extension of this agricultural imagery, with the farmer's implement changed to a [[shepherd's crook]] rather than a reaping tool. Compare similar developments in the [[Dutch language|Dutch]] words for Opiliones: {{wikt-lang|nl|hooiwagen}} (literally meaning “[[hay]]-wagon”) and in southern dialects {{wikt-lang|nl|koewachter}} (literally “cowherd”, one who herds cattle).

English speakers may colloquially refer to species of Opiliones as "{{wikt-lang|en|daddy longlegs|i=-}}" or "granddaddy longlegs". However, this name is also used for two other distantly related groups of [[arthropod]]s: the crane flies of the superfamily [[Tipuloidea]], as well as the [[Pholcidae|cellar spiders]] of the family Pholcidae (which may be distinguished as "{{wikt-lang|en|daddy long-legs spider|daddy long-leg spiders|i=-}}"), because of their similar appearance.{{cn|date=February 2025}}

==Further internal navigation links==
{{Arachnida}}
{{Opiliones}}

==References==
{{Reflist|30em|refs=

<ref name="WCO-lite">{{Cite web|title=Opiliones|url=https://wcolite.com|access-date=2024-07-10|website= Kury, A. et al. (2023). WCO-Lite: World Catalogue of Opiliones}}</ref>

<ref name="Hallan">{{Cite web|title=Opiliones|url=http://insects.tamu.edu/research/collection/hallan/Acari/Family/Opiliones1.htm|access-date=2024-07-10|website= Joel Hallan's Biology Catalog (Archive version. August 2017)|archive-url=https://web.archive.org/web/20170804222539/http://insects.tamu.edu/research/collection/hallan/Acari/Family/Opiliones1.htm |archive-date=2017-08-04 }}</ref>

}}

==External links==
* {{Commons category-inline}}
* {{Wikispecies-inline}}
* Adriano Kury: National Museum of Rio de Janeiro [http://www.museunacional.ufrj.br/mndi/Aracnologia/opiliones.html Classification of Opiliones]—A synoptic taxonomic arrangement of the order Opiliones, down to family-group level, including some photos of the families
* [http://www.cirrusimage.com/harvestman.htm Harvestman: Order Opiliones]—Diagnostic photographs and information on North American harvestmen
* [http://www.xs4all.nl/~ednieuw/Spiders/Opiliones/Opiliones.htm Harvestman: Order Opiliones]—Diagnostic photographs and information on European harvestmen
* University of Aberdeen: [http://www.abdn.ac.uk/rhynie/harvestmen.htm The Rhynie Chert Harvestmen] (fossils)
* [https://web.archive.org/web/20170804222539/http://insects.tamu.edu/research/collection/hallan/Acari/Family/Opiliones1.htm Joel Hallan's Biology Catalog (Archive only before 2017]

{{Opiliones}}
{{Taxonbar|from=Q19116}}
{{Authority control}}

[[Category:Harvestmen| ]]
[[Category:Arachnid orders]]
[[Category:Extant Early Devonian first appearances]]
[[Category:Taxa named by Carl Jakob Sundevall]]