Editing Horned lizard (section)

==Defenses==
[[File:Phrynosoma orbiculare 1.jpg|thumb|left|Mexican Plateau horned lizard (''Phrynosoma orbiculare'') near Xalapa de Enríquez, Veracruz, Mexico, showing blood squirted from the eye as defensive behavior (20 April 2011)]]
Horned lizards use a variety of means to avoid [[predation]]. Their coloration generally serves as [[camouflage]]. When threatened, their first defense is to remain motionless to avoid detection. If approached too closely, they generally run in short bursts and stop abruptly to confuse the predator's visual acuity. If this fails, they puff up their bodies to cause them to appear more horned and larger so that they are more difficult to swallow.<ref>{{cite journal | last=Winton | first=W. M. | title=Habits and Behavior of the Texas Horned Lizard, ''Phrynosoma cornutum'', Harlan. I | journal=Copeia | publisher=JSTOR | issue=36 | date=1916-10-24 | volume=36 | pages=81–84 | issn=0045-8511 | doi=10.2307/1436504 | jstor=1436504 | url=https://www.biodiversitylibrary.org/part/85685 }}</ref>

At least eight species (''P. asio'', ''P. cornutum'', ''P. coronatum'', ''P. ditmarsi'', ''P. hernandesi'', ''P. orbiculare'', ''P. solare'', and ''P. taurus'') are also able to [[Autohaemorrhaging|squirt an aimed stream of blood]] from the corners of the eyes for a distance up to {{convert|5|ft|m|abbr=on}}.<ref name="Middendorf III et al., 2001"/><ref name="Sherbrooke & Middendorf III, 2001"/><ref name="Sherbrooke & Middendorf III, 2004"/><ref name=hodges/> They do this by restricting the blood flow leaving the head, thereby increasing blood pressure and rupturing tiny vessels around the [[eyelid]]s.  The blood not only confuses predators but also tastes foul to [[dog|canine]] and [[Felinae|feline]] predators. It appears to have no effect against predatory [[bird]]s. Only three closely related species (''P. mcallii'', ''P. modestum'', and ''P. platyrhinos'') are certainly known to either be unable to squirt blood or only do it extremely rarely.<ref name="Sherbrooke & Middendorf III, 2001"/>

While previous thought held that compounds were added to the blood from glands in the ocular sinus cavity, current research has shown that the chemical compounds that make up the defense are already in the circulating blood.<ref name="Sherbrooke & Middendorf III, 2001"/><ref name="Sherbrooke & Middendorf III, 2004"/> It is possible that their diet of large quantities of venomous [[harvester ant]]s could be a factor; however, the origin and structure of the chemicals responsible are still unknown. The blood-squirting mechanism increases survival after contact with canine predators;<ref name="Sherbrooke & Middendorf III, 2004"/> the trait may provide an evolutionary advantage. Ocular autohemorrhaging has also been documented in other lizards,<ref name="Sherbrooke, 2000"/> which suggests blood-squirting could have evolved from a less extreme defense in the ancestral branch of the genus. Recent phylogenic research supports this claim, so the species incapable of squirting blood apparently have lost the adaptation for reasons yet unstudied.<ref name="Leaché and McGuire (2006)"/>

To avoid being picked up by the head or neck, a horned lizard ducks or elevates its head and orients its cranial horns straight up, or back. If a predator tries to take it by the body, the lizard drives that side of its body down into the ground so the predator cannot easily get its lower jaw underneath.{{citation needed|date=September 2017}}