The Texas Horned Lizard (Phrynosoma cornutum), nicknamed the “Horny Toad,” is a distinctive reptile native to the arid and semi-arid landscapes of the American Southwest. This flat-bodied lizard is equipped with a crown of prominent horns and a spiky integument, reflecting a life under constant threat from various predators, including snakes, coyotes, and birds of prey. Its survival relies upon a sophisticated, multi-layered defense system that begins with remaining unseen and escalates to one of the most unusual biological behaviors in the animal kingdom.
Avoiding Detection: Camouflage and Immobility
The primary defense is crypsis, or camouflage, which capitalizes on the lizard’s natural appearance. Its mottled coloration, featuring browns, tans, and grays, allows the Texas Horned Lizard to blend seamlessly with the sandy and rocky substrates where it lives. The flattened body shape allows the lizard to press itself close to the ground to minimize shadow, further disrupting its outline. This reliance on visual deception is particularly effective against visually oriented predators like avian hunters.
When a potential threat is sensed, the lizard’s immediate reaction is to freeze completely, relying solely on its cryptic coloration. This immobility is a form of “stand your ground” defense used until the predator passes by. If disturbed, the lizard will often run in short, rapid bursts before suddenly stopping and freezing again to confuse the attacker. This tactic avoids the high energy cost and increased visibility that comes with a prolonged flight response.
Physical Deterrence and Evasion Tactics
Should camouflage fail, the Texas Horned Lizard transitions to active physical defenses designed to make it unappetizing or difficult to consume.
Body Inflation and Threat Displays
A common intimidation tactic involves rapid body inflation, where the lizard quickly puffs itself up with air to appear larger. This action causes the numerous spiny scales and sharp cranial horns to project outward, making the lizard harder for a predator to swallow whole. Lizards may also engage in a threat display, which includes opening the mouth in a gape, hissing, and lunging toward the perceived danger.
Horns and Thanatosis
The sharp horns on the back of the head are part of the skull and serve as a physical deterrent. These horns have been found to puncture the throats of attacking snakes, which deters future predation attempts. In a direct confrontation, the lizard may lower its head and attempt to charge or butt small threats, using its horns as a weapon. If all else fails, a lizard may roll over and play dead, a form of feigned death known as thanatosis, to confuse a predator.
The Specialized Defense: Directing a Blood Jet
The most remarkable and specialized defense is the ability to squirt a jet of blood from its eyes, a high-cost behavior used as a last resort. The lizard achieves this by deliberately restricting blood flow to increase pressure within the ocular sinuses, which are specialized chambers located around the eyes. This pressure causes small vessels to rupture, ejecting a stream of blood from ducts near the eyelids, which can be sprayed with surprising accuracy up to five feet away.
This is not just a startling spray; the blood is a chemical weapon specifically tailored to deter certain mammalian predators. The lizard’s diet, which consists mainly of noxious harvester ants (Pogonomyrmex), provides chemical compounds that are sequestered into the lizard’s bloodstream. These chemicals render the blood foul-tasting and repugnant, particularly to canids such as coyotes and foxes. By aiming the blood jet at the predator’s mouth or eyes, the lizard causes immediate revulsion and can create a learned aversion in the attacker.