The horned lizards (Phrynosoma spp.) are a genus of North American lizards that are found in the United States and further south in Mexico. The most common species, the Texas horned lizard (Phrynosoma cornutum) can actually be found as far north as Colorado and Kansas, and they are apparently pretty common to come across by the people who live in these areas. Not only are they common in the wild, but they are also commonly kept as pets, so you might even see them in a pet store nearby.
A Texas horned lizard (Phrynosoma cornutum). Image by Burton Robert, U.S. Fish and Wildlife Service, posted as Public Domain.
Most horned lizards eat ants, and their body is even covered with a thick and horny skin that prevents the ants from biting through it. Since the ants cannot harm it, they can pretty much find an ant colony and eat as much as they want without having to do much besides walk around and collect ants to eat, so they are not really adapted to being fast at all.
Their round body and slow manner has lead them to having pet names such as horny toads, but they are in no way related to the amphibious toads at all, but are rather a type of lizard.
There are a total of 22 species of horned lizard, and 15 of these are native to the United States. Out of these 22 species, at least 8 of them has a very cool defensive ability that we want to take a closer look at; the ability to shoot blood out of their eyes.
A close-up of the head of a Texas horned lizard. Image by Ben Goodwyn, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license.
Some people believe that even more of the horned lizard species have this defensive ability, but it has been been documented in any of the remaining species yet.
Autohaemorrhaging
The “fancy” name for secreting blood from your body as a defensive reflex is autohaemorrhaging, and the horned lizards are not the only type of animal that is capable of this. However, this defense is not really as flashy as the behavior displayed by the horned lizards; for instance, the European grass snake (Natrix natrix) will feign death when threatened, and will secrete blood from its mouth and nose during this act.
A grass snake in the process of playing dead! We can’t see any blood here, but they are able to secret it if they want to. Image by Piet Spaans Viridiflavus, posted with the Creative Commons Attribution-Share Alike 2.5 Generic license.
The autohaemorrhaging ability of the horned lizard is a lot more extravagant, and what it actually does it to shoot blood from its eyes! When the animal is faced with danger, the pressure on the blood vessels located just above the eyes will increase, which leads to it rupturing. This squirts blood out from the eyes and in a straight line ahead of the lizard. At most, the blood can be squirted 1.5 meters!
Fending of predators
The reason why they have this ability to squirt blood out of their eyes in the first place is to fend off attacks from predators such as foxes and coyotes. As I mentioned above, the horned lizards are snow walkers, so they had to evolve a different approach to dealing with predators, and this blood squirting seem to do the job just fine.
A coyote, one of the predators that would gladly have a horned lizard for dinner. Image by Yathin S Krishnappa, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license.
The blood also contains a toxic that seem to repel away canine predators. No one really knows what chemical is used, but researchers proved that foxes shy away from the blood by smearing horned lizard blood onto mice, then give the mice to a fox. The foxes responded very differently to these mice compared to the mice smeared in blood by other animals, and even shows behavior such as shaking its head, and it spent a lot longer time to kill the mouse that was smeared with the blood of the horned lizard. If you are interested, then you should check out the original research paper about this experiment to learn more.
Anyway, the blood is not only gross, the toxin found within it is repelling the predators away, so both canines such as the coyotes and foxes, as well as cats and other felines are scared away when hit with blood in their faces. The horned lizards are still not 100 % safe, because all of these animals are still able to dodge the blood squirt and kill them, so they better be sure that they will hit, or else they could become dinner!
A video of the blood shooting in action!
Thanks for reading
I hope you enjoyed this post about the unique defensive ability of the horned lizards! Thanks for reading. If you want to learn more, then I suggest giving the links in the post a go, or check out the video above to see it for yourself.
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