Editing Flea (section)

== Life cycle and development ==
[[File:A dog flea (Ctenocephalides canis); adult, pupa, egg and lar Wellcome V0022501EL.jpg|thumb|upright|[[Ctenocephalides canis|Dog flea]] (from top) larva, egg, pupa and adult]]

Fleas are [[holometabolous]] insects, going through the four [[Biological life cycle|lifecycle]] stages of [[egg]], [[larva]], [[pupa]], and [[imago]] (adult). In most species, neither female nor male fleas are fully mature when they first emerge but must feed on blood before they become capable of reproduction.<ref name="Florida"/> The first blood meal triggers the maturation of the ovaries in females and the dissolution of the testicular plug in males, and copulation soon follows.<ref name=Krasnov44>{{cite book|author=Krasnov, Boris R. |title=Functional and Evolutionary Ecology of Fleas: A Model for Ecological Parasitology |url=https://books.google.com/books?id=tkvr8h8zxFwC&pg=PA44 |year=2008 |publisher=Cambridge University Press |isbn=978-1-139-47266-1 |pages=44–54}}</ref> Some species breed all year round while others synchronise their activities with their hosts' life cycles or with local environmental factors and climatic conditions.<ref name=Krasnov64>{{cite book|author=Krasnov, Boris R. |title=Functional and Evolutionary Ecology of Fleas: A Model for Ecological Parasitology |url=https://books.google.com/books?id=tkvr8h8zxFwC&pg=PA44 |year=2008 |publisher=Cambridge University Press |isbn=978-1-139-47266-1 |pages=64–67}}</ref> Flea populations consist of roughly 50% eggs, 35% larvae, 10% pupae, and 5% adults.<ref name="Crosby" />

=== Egg ===
The number of eggs laid depends on species, with batch sizes ranging from two to several dozen. The [[fecundity|total number of eggs produced in a female's lifetime]] (fecundity) varies from around one hundred to several thousand. In some species, the flea lives in the host's nest or burrow and the eggs are deposited on the substrate,<ref name=Krasnov44/> but in others, the eggs are laid on the host itself and can easily fall off onto the ground. Because of this, areas where the host rests and sleeps become one of the primary [[habitat]]s of eggs and developing larvae. The eggs take around two days to two weeks to hatch.<ref name="Crosby"/>

=== Larva ===
[[File:Flea Larva.jpg|thumb|upright|Flea larva]]

Flea larvae emerge from the eggs to feed on any available organic material such as dead insects, faeces, [[Biological specificity|conspecific]] eggs, and vegetable matter. In laboratory studies, some dietary diversity seems necessary for proper larval development. Blood-only diets allow only 12% of larvae to mature, whereas blood and yeast or dog chow diets allow almost all larvae to mature.<ref>{{cite journal |last1=Silverman |first1=Jules |last2=Appel |first2=Arthur |date=March 1994 |title=Adult Cat Flea (Siphonaptera: Pulicidae) Excretion of Host Blood Proteins in Relation to Larval Nutrition |url=http://www4.ncsu.edu/~jsilver/Silverman%20and%20Appel%201994.pdf |journal=Journal of Medical Entomology |issue=2 |pages=265–271 |doi=10.1093/jmedent/31.2.265 |access-date=18 July 2014 |volume=31 |pmid=7910638 |archive-date=25 July 2014 |archive-url=https://web.archive.org/web/20140725150050/http://www4.ncsu.edu/~jsilver/Silverman%20and%20Appel%201994.pdf |url-status=dead }}</ref> Another study also showed that 90% of larvae matured into adults when the diet included nonviable eggs.<ref>{{Cite journal |last=Shryock |first=J. |date=2006 |title=Time Spent by Ctenocephalides felis (Siphonaptera: Pulicidae) Larvae in Food Patches of Varying Quality |journal=Environmental Entomology |doi= 10.1603/0046-225x-35.2.401|volume=35 |issue=2 |pages=401–404|doi-access=free }}</ref> They are blind and avoid sunlight, keeping to dark, humid places such as sand or soil, cracks and crevices, under carpets and in bedding.<ref name=Hinkle/> The entire larval stage lasts between four and 18 days.<ref>{{Cite web|url=https://www.orkin.com/other/fleas/fleas-life-cycle|title=Flea Life Cycle: Eggs, Larvae, etc.|website=Orkin.com|date=11 April 2018|language=en|access-date=2019-09-13}}</ref>

=== Pupa ===
Given an adequate supply of food, larvae [[pupate]] and weave [[silk]]en cocoons after three larval stages. Within the cocoon, the larva molts for a final time and undergoes metamorphosis into the adult form. This can take just four days, but may take much longer under adverse conditions, and there follows a variable-length stage during which the pre-emergent adult awaits a suitable opportunity to emerge. Trigger factors for emergence include vibrations (including sound), heat (in warm-blooded hosts), and increased levels of [[carbon dioxide]], all of which may indicate the presence of a suitable host.<ref name="Crosby" /> Large numbers of pre-emergent fleas may be present in otherwise flea-free environments, and the introduction of a suitable host may trigger a mass emergence.<ref name=Hinkle/>

=== Adult ===
Once the flea reaches adulthood, its primary goal is to find blood and then to reproduce.<ref>{{cite web|url=http://edis.ifas.ufl.edu/IG087 |title=Fleas |author1=Koehler, P.G. |author2=Pereira, R.M. |author3=Diclaro, J.W. |publisher=Edis.ifas.ufl.edu |access-date=11 November 2016}}</ref> Female fleas can lay 5000 or more eggs over their life, permitting rapid increase in numbers.<ref name="loc.gov">{{cite web|url=https://www.loc.gov/rr/scitech/mysteries/flea.html |title=How long is the life span of a flea? |work=Everyday Mysteries: Fun Science Facts from the Library of Congress |publisher=Loc.gov |date=2 July 2013 |access-date=11 November 2016}}</ref> Generally speaking, an adult flea only lives for 2 or 3 months. Without a host to provide a blood meal, a flea's life can be as short as a few days. Under ideal conditions of temperature, food supply, and humidity, adult fleas can live for up to a year and a half.<ref name="loc.gov"/> Completely developed adult fleas can live for several months without eating, so long as they do not emerge from their [[puparium|puparia]]. Optimum temperatures for the flea's life cycle are {{convert|21|to|30|C|F}} and optimum humidity is 70%.<ref name="Piper, Ross 2007"/>

Adult female rabbit fleas, ''[[Spilopsyllus cuniculi]]'', can detect the changing levels of [[cortisol]] and [[corticosterone]] hormones in the rabbit's blood that indicate it is getting close to giving birth. This triggers sexual maturity in the fleas and they start producing eggs. As soon as the baby rabbits are born, the fleas make their way down to them and once on board they start feeding, mating, and laying eggs. After 12 days, the adult fleas make their way back to the mother. They complete this mini-migration every time she gives birth.<ref name="Piper, Ross 2007">[[Ross Piper|Piper, Ross]] (2007), ''Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals'', [[Greenwood Press]].</ref>