Reptiles
Regal Horned Lizard
Phrynosoma solare · also called regal horned lizard, regal horned toad
The regal horned lizard is the biggest of the horned lizards — a flat, round, spiky reptile the size of a saucer, with a crown of four large horns fused into a fringe at the back of its head. It lives on a diet almost entirely of stinging harvester ants, and when a coyote or a dog picks it up, it defends itself by firing a jet of foul-tasting blood out of its own eye.
Overview
The regal horned lizard lives in the Sonoran Desert of Arizona and north-western Mexico, on desert flats and washes with harvester ant colonies. It has a body of 8–12 cm and a total length up to about 16 cm, flat and disc-shaped, sandy brown, with a continuous fringe of horns at the back of the head.
An ant specialist
It eats mainly harvester ants, which are armoured and venomous and which most animals avoid. Because the ants are small and low in energy, the lizard eats a great many at once, has a large stomach, digests slowly, and produces a throat mucus that binds the ants and helps neutralise their stings.
Blood from the eyes
Seized by a coyote, fox, or dog, the lizard raises the pressure in its head until vessels at the corners of the eyes rupture, firing a thin stream of blood a metre or more. The blood carries compounds — apparently from the harvester ants — that taste foul to canids, which drop the lizard and shake their heads. The trick does not work on birds.
Status
The regal horned lizard is Least Concern, common in good habitat, but local populations decline where invasive fire ants displace the native harvester ants, where land is developed, and on roads, where the lizards sit still rather than flee.
Regal Horned Lizard: common questions
Do horned lizards really shoot blood from their eyes?
Yes, several horned lizard species do, and the regal horned lizard is one of them. Faced with a canid predator that has it in its jaws, the lizard restricts the blood flow leaving its head, which raises the pressure until thin-walled sinuses in the corners of the eye sockets burst and release a jet of blood, sometimes with enough force to travel a metre or more and to hit the attacker in the face and mouth. The lizard can lose a noticeable fraction of its blood volume doing this, so it is a last resort, used only when other defences have failed and usually only against dogs, coyotes, and foxes.
Why does the blood work on coyotes but not on hawks?
The defence seems to depend on chemistry rather than surprise. Analysis of the blood shows it contains substances that dogs and coyotes find strongly distasteful, and these appear to come, at least in part, from the harvester ants the lizard eats, whose own venom includes irritating compounds. A canid that gets a mouthful reacts with obvious disgust, gaping and head-shaking, and drops the lizard. Birds of prey, which hunt horned lizards from the air, do not show this reaction, and against them the blood squirt is not effective, so the lizard relies on camouflage and its spines instead.
How can it eat so many stinging ants?
Harvester ants are well defended, with a hard exoskeleton and a painful sting, and most animals avoid them, which is exactly why they are a reliable food source for a specialist that can handle them. The regal horned lizard has several adaptations. Its throat glands produce a thick mucus that coats and clumps the ants as they are swallowed, tangling their legs and jaws and helping to inactivate the venom before the ants can sting the stomach lining. The lizard also has a slow, deliberate feeding style, taking one ant at a time from the edge of a trail, and a large, muscular stomach to process a big load of low-value prey.
Is the regal horned lizard endangered?
It is listed as Least Concern and remains common in good habitat, but it faces real local pressures. The biggest is the spread of invasive fire ants and Argentine ants, which displace the native harvester ants the lizard depends on and are not a suitable substitute food. Urban and agricultural development removes habitat, roads kill many lizards, which tend to sit still rather than flee, and the animals are still sometimes collected for the pet trade despite being difficult to keep alive because of their specialised diet. In parts of its United States range it is protected and cannot legally be taken.