Horned lizards are small round flat lizards with spines covering their bodies. Their bodies and tails are short, and their coloration is generally cryptic, blending in with the environment they inhabit.They are "sit-and-wait" predators with specialized teeth and digestive systems due to their staple food, ants.

Most horned lizards can squirt blood from sinuses in their eyes as a defense mechanism. This character is mapped on the phylogeny below. Click here for a picture of a P. asio after having engaged in this behavior. This repels many would-be predators. Their spines are another powerful defense. Even if a snake manages to swallow a horned lizard, this often kills the snake. This would encourage selection in snakes to avoid the spiky prey.

The Australian thorny devil (Moloch horridus) looks very similar to horned lizards. They have the same general body shape, complete with the characteristic spines. They even eat the same thing: lots of ants! The Moloch , however, is not related to the horned lizards. This is a case of convergence, evolving in two separate parts of the world because they fill similar niches in similar habitats.

Phrynosoma regulate their temperature behaviorally. If they are too cold, they will bask in the sun and/or sit on hot surfaces. In addition to this, many change their posture to help maximize or minimize the amount of heat they soak up from the sun. To warm up, they expand their ribs and position their bodies perpendicular to the sun's rays in order to maximize the amount of heat they absorb from the sun. To keep from overheating, they compress their ribs (narrowing the body) and position their bodies parallel to the sun. This minimizes the amount of sunlight that has contact with their skin.

Horned lizards are in a very precarious position at the present. With human development has come an excess of water. This has attracted the water-loving Argentine ants, which are driving out the native ant species. These native ants just happen to be the main diet of horned lizards. Argentine ants are not as palatable, which is causing many Phrynosoma to decline.

Other names for horned lizards: horny toads, horned toads, horned frogs.