Today’s Wonder of the Day was inspired by Blake from Boston, MA. Blake Wonders, “How do horned lizards shoot blood from their eyes?” Thanks for WONDERing with us, Blake!
Bobcat: Mr. Lizard, I'm going to eat you now.
Lizard: Umm…I'd prefer that you didn't, if you don't mind.
Lizard: I actually don't taste anything like chicken, if that's what you've heard.
Bobcat: No way! Can you really do that?
Lizard: Try me.
As it turns out, he was not. There are 17 species of horned lizards that live in dry, desert areas from Guatemala and Mexico up through the western United States and even into southern Canada.
Their first line of defense is camouflage. Although the various species differ in coloring and the exact number and placement of horns, they usually blend in very well with their desert surroundings. When predators approach, they usually try to stay still to avoid detection.
If they are detected, they may or may not try to run away. They have wide, flat bodies with short legs, so they're not very fast. Some predators, such as rattlesnakes, don't usually chase their prey, so they may run away from these predators.
Many predators can easily outrun and catch a horned lizard. When caught, horned lizards will often stretch out and puff themselves up to appear as large as possible. They do this to deter predators who eat their prey whole. If the predators can't get the whole lizard in their mouths, they may move on.
As a last resort, horned lizards may use one final defense mechanism that's particularly effective against predators like bobcats, wolves, and coyotes. They shoot blood from their eye sockets! This usually frightens predators enough to make them flee. Fortunately for humans, horned lizards rarely shoot blood at people.
How do they do it? Horned lizards can contract the muscles around their eyes, cutting off blood flow back to the heart. Blood continues to flow into the eye area where it fills the ocular sinuses with blood.
They then continue to contract those same muscles rapidly, increasing pressure on the thin sinus membranes until they rupture, releasing a stream of blood that can shoot up to four feet from the eye! Scientists call this process auto-hemorrhaging.
If necessary, horned lizards can repeat this process several times within a short period. It also has a practical use beyond defense. In the areas where they live, it's common for them to get dirt and dust in their eyes. They can carefully control the auto-hemorrhaging process to remove irritating particles from their eyes without fully rupturing their sinuses.