Lizards belonging to the genus Phrynosoma, at least 8 species within this genus, have the ability to bleed from their eyes when necessary, and their blood contains special chemicals.
Each animal species possesses unique defensive strategies to protect themselves, and some lizards are no exception.
Some horned lizards can shoot blood from their eyes up to 1.5 meters. (Illustration: Reddit).
They can use their horns to stab, camouflage, or flatten their bodies to escape danger, but when it comes to larger predators, the approach is different.
Some species of lizards will resort to shooting blood from their eyes to deter their enemies.
This process is known as autohemorrhaging, and for horned lizards, one of the main motivations for this behavior is self-defense.
Several studies have investigated how these lizards respond to various predators and threats, such as hawks or snakes.
There are even lizards that bleed when encountering dogs; however, not all of them defend themselves in this manner.
Where Does the Blood Come From?
The eye socket of some lizard species is directly connected to blood vessels in their eye cavity.
When confronted with a threat, the blood circulation is immediately affected.
Blood flow to the head is increasingly restricted and redirected to the eye socket, where pressure builds up. This allows the oculi muscles adjacent to the pressured sinuses to contract.
When the muscles contract, these sinuses burst, and a stream of blood held in the eye duct is expelled, potentially reaching up to 1.5 meters.
These lizards can continue to shoot blood until they successfully scare off their foe.
To effectively defend themselves, their blood contains substances that are irritating to predators.
Studies have found several additional chemicals in their blood that emit unpleasant odors or even suppress the appetite of the enemy.
One hypothesis suggests that the chemicals originate from ant venom, as horned lizards enjoy eating poisonous ants without suffering health consequences, seemingly neutralizing the ants’ venom.
After expelling blood to frighten prey, the lizards have another special mechanism in their eyes.
These lizards possess a third eyelid, a translucent membrane that covers their eyes.
This membrane, called the nictitating membrane, is present in all lizard species.
After the blood is expelled, the nictitating membrane removes the blood as it sweeps across the surface of the eyeball, pushing it to the back corner of the eye, and excess blood will fall out.
Evolutionary studies indicate that the characteristic of blood shooting has been adopted and became prevalent when lizards began facing predation pressure from canine species.
Some species of horned lizards currently lack this defense mechanism, suggesting they may have lost the ability to do so through the process of evolution. However, the reason for this loss remains a mystery.
Autohemorrhaging for self-defense is not limited to horned lizards. Some snake species, such as rosy boas, kingsnakes, and eastern hognose snakes, also expel blood, not just from their eyes but also from their nostrils or cloaca (the common opening for the reproductive, intestinal, and urinary tracts).
