Horned lizard

The horned lizards belong to the genus *Phrynosoma*. This group of North American reptiles includes 21 recognized species. Their common names, like "horny toad," describe their unique bodies. They have flattened, rounded shapes and blunt snouts. The name *Phrynosoma* actually means "toad-bodied."

These lizards are highly adapted to arid or semiarid environments. They often move sluggishly or remain motionless to avoid being seen. Their survival depends on specialized physical traits and clever behaviors.

One remarkable adaptation is a process called rain-harvesting. This behavior helps lizards find water in dry lands. When rain falls on the scales of their backs, water moves toward their mouths. This happens through capillary action, which is the passive transport of liquid through tiny channels.

While this ability varies between species, it is a vital way to stay hydrated. Additionally, their modified scales on their backs and sides help prevent water loss through the skin. Unlike true toads, these lizards lack a urinary bladder.

To survive, horned lizards use several distinct defense mechanisms. Their first line of defense is camouflage to blend into the environment. If a predator approaches, they may run in short bursts and stop suddenly. This behavior is meant to confuse the predator's visual acuity. They can also puff up their bodies to appear larger and more difficult to swallow.

To protect their heads, they can orient their cranial horns straight up or back. If a predator attacks their body, they drive that side into the ground to prevent the predator from getting its jaw underneath.

At least eight specific species can perform a very unusual defense. These species include *P. asio*, *P. cornutum*, and *P. solare*, among others. They can squirt an aimed stream of blood from the corners of their eyes. They achieve this by restricting blood flow leaving the head. This increases their blood pressure until tiny vessels around the eyelids rupture.

This blood tastes foul to canine and feline predators, though it does not affect birds. Scientists once thought glands added chemicals to this blood. Now, research shows the defensive compounds are already in their circulating blood. It is possible their diet of venomous harvester ants provides these chemicals.

History shows that human activity has heavily impacted these populations. In the early to mid-20th century, the pet trade took thousands of lizards from the wild. Most of these lizards died because they could not meet their specialized nutritional needs. They require specific amounts of formic acid from harvester ants to survive.

Because of this, Texas passed protective legislation in 1967. Most other U.S. states followed with similar laws by the early 1970s. However, some species are still sold in Mexican pet markets today.

Today, many species face significant threats of population decline. Habitat fragmentation from roads and real estate development is a major cause. The use of pesticides and the planting of non-native grasses also harm them.

An invasive species, the fire ant (*Solenopsis invicta*), is a serious threat. Fire ants compete with the native ants that horned lizards need for food. Because horned lizards do not eat fire ants, this competition displaces their food source. Domestic cats and dogs also put pressure on their numbers.

The Texas horned lizard (*Phrynosoma cornutum*) is a notable example of these challenges. It is the largest and most widely distributed American species. It is also the official state reptile of Texas. However, it has disappeared from almost half of its original geographic range.

In 2014, the Center for Biological Diversity petitioned for it to be listed as endangered in Oklahoma. This highlights how these specialized reptiles are struggling to survive in a changing world.