Resource: Horned Lizard

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Unmistakable for the spines protruding from its head, throat, and sides, the horned lizard is a small (6–12 cm), carnivorous, desert-dwelling reptile. Its squat, stubbled shape is nothing like the sleek, smooth body form that characterizes most lizards. In fact, its outward appearance has earned the horned lizard another nickname: "horned toad."

The dozen or so recognized horned lizard species range in hot, dry environments across the U.S. and Mexico, extending as far north as southern Canada and as far south as Guatemala. In nature, organisms evolve with certain physical and behavioral adaptations that help them survive in their habitat, and the horned lizard is no exception. Like many other desert animals, the horned lizard is camouflaged to blend in with the surrounding environment, which helps it surprise prey and hide from predators. An unusual desert adaptation displayed by the horned lizard employs the scales and ridges on its tail and back to channel rain and moisture droplets to its mouth.

The horned lizard spends most of its day seeking to regulate its body temperature, which, as with all lizards, fluctuates according to the environment it's in. In the cooler hours of daylight, the horned lizard forages in the open landscape for its preferred food—harvester ants—and other small prey. The methodical feeding behavior exhibited by the horned lizard renders it vulnerable to predators, which include coyotes, foxes, snakes, and raptors. When a horned lizard senses danger, its initial reaction is to flatten itself against the ground and freeze in place. By doing so, it casts very little shadow, making it even harder for predators to locate.

Even though its spiny armor may deter certain predators, the horned lizard exhibits additional defensive adaptations. First, it can inflate its body to resemble a spiny balloon, making it appear larger and harder to swallow. Second, some species squirt blood from ducts in the corners of their eyes. The blood, which contains chemicals that give it an unappealing taste, can travel up to three feet and startles predators on contact. While the horned lizard may be adept at avoiding most predators, studies attribute its declining population to several other factors, including habitat loss resulting from agricultural and urban development, displacement of the harvester ant by fire ant populations, and toxicity from exposure to pesticides.

To learn more about the physical characteristics of the desert and the animals that inhabit it, check out Desert Biome.

To learn more about the role of natural selection in the evolution of camouflage, check out Evolution of Camouflage, Masters of Disguise and Seeing Through Camouflage.

To learn more about the various strategies animals use to defend themselves, check out check out Animal Defenses.

Print Questions for Discussion

• What are some of the physical adaptations that enable horned lizards to exist in their extreme environment?
• What are some of the behavioral adaptations that enable horned lizards to exist in their extreme environment?
• How does the ability to change its skin color help a horned lizard survive the desert?
• Name two other defenses a horned lizard has that protect it from predators.