Horned Lizards Squirt Blood From Their Eyes

Imagine being a coyote, eyeing a spiky, toad-like lizard. You pounce, expecting an easy meal, and suddenly, a stream of blood erupts from the lizard's eyes, hitting you squarely in the face. This isn't a scene from a horror movie; it's a real and highly effective defense mechanism employed by horned lizards, often called "horny toads." These small, North American reptiles can intentionally rupture tiny blood vessels around their eyes and squirt jets of blood up to several feet.

The mechanism behind this gory display is a sophisticated form of self-pressurization. When a horned lizard feels sufficiently threatened, it restricts blood flow leaving its head. This rapidly increases the blood pressure in specialized sinuses around its eyes. Once the pressure reaches a critical point, the capillaries in the eye sockets burst, sending a directed stream of blood outwards. It's a precise, controlled maneuver, not a random rupture, and they can even aim.

So, why does blood-blasting work? For some predators, like coyotes and domestic dogs, the sudden taste and smell of reptilian blood is a powerful deterrent. It's thought to be foul-tasting, or perhaps the sheer shock and unexpectedness of the attack is enough to make the predator recoil. The blood also contains specific chemicals that may be unpleasant to canids. For birds of prey, however, this defense is less effective, as they don't seem to be bothered by the blood and rely more on sight than smell.