The creature commonly known as the “horny toad” is, in fact, a lizard belonging to the genus Phrynosoma, scientifically referred to as the horned lizard. These reptiles are easily distinguished by their flat, toad-like bodies and the prominent horn-like spines on their heads, which inspired their common name. Unlike many other lizards with generalized diets, the horned lizard is a specialized predator. This extreme dietary focus has shaped their biology and behavior, making them some of the most specialized reptiles in arid North American ecosystems.
The Foundation of Their Diet
The vast majority of a wild horned lizard’s diet consists of ants, a specialization known as myrmecophagy. The preference is overwhelmingly for harvester ants, primarily those in the genus Pogonomyrmex. For example, the regal horned lizard (Phrynosoma solare) may have a diet composed of up to 90 percent harvester ants, while the Texas horned lizard (Phrynosoma cornutum) consumes ants for up to 99 percent of its prey items.
Ants are low-yield food, offering relatively few nutrients compared to their indigestible chitinous exoskeleton. Because of this, the specialized prey is consumed in massive quantities. A single adult horned lizard can consume dozens to over a hundred ants daily to meet its energy and nutrient requirements. While the diet is dominated by ants, they opportunistically consume other small invertebrates, such as small beetles, grasshoppers, and spiders.
Specialized Hunting and Feeding Behavior
Horned lizards are ambush predators, employing a “sit-and-wait” foraging strategy near ant trails or colony entrances. Their cryptic coloration allows them to blend seamlessly into the substrate, making them nearly invisible as they wait for prey to pass. They rely on quick, precise action, capturing the ants with a rapid flick of their sticky tongue rather than pursuing them or using their jaws.
Consuming harvester ants poses a significant challenge because these insects are capable of biting and delivering a venomous sting. To counter this defense, the horned lizard has evolved a unique feeding mechanism. As they swallow the ants whole, the lizards produce copious amounts of mucus in the pharynx and esophagus. This mucus acts to immobilize and bind the ants, compacting them into a ball before they reach the stomach.
The Implications of a Specialized Diet
The ant-heavy diet provides the horned lizard with more than just basic nutrition; it supplies specific chemical components. Harvester ants contain formic acid, which the lizard’s system utilizes. This acid may metabolize to yield water, which is highly beneficial in their arid environment. It is also thought to lower the digestive tract’s pH, which may suppress harmful bacteria.
The ingestion of ants is also believed to play a role in one of the lizard’s most unusual defense mechanisms: the ability to squirt blood from the corners of its eyes. This specialization has significant practical consequences, evidenced by the difficulty in maintaining them in captivity. A general insect diet, such as standard crickets, fails to replicate the complex nutritional profile of harvester ants, often leading to the lizard’s decline.