A highly specialized diet
The Regal Horned Lizard (Phrynosoma solare) is a myrmecophage, or ant-eater, with a diet that can consist of up to 90% harvester ants from the genus Pogonomyrmex. This is a challenging food source. Harvester ants provide low nutritional returns due to their high proportion of indigestible chitin, and they possess a formidable defense. Their venom is among the most toxic of all insects, composed of peptides and proteins that cause intense, long-lasting pain in vertebrates by modulating voltage-gated sodium channels. The venom of the Maricopa harvester ant (Pogonomyrmex maricopa) has a median lethal dose (LD50) of 0.12 mg/kg in mice, making it substantially more potent than honeybee venom.
To overcome these challenges, the lizard has a suite of remarkable adaptations. It uses a sticky tongue to capture ants one by one, swallowing them whole and alive. Specialized cells in its pharynx and esophagus produce copious amounts of thick mucus that envelop each ant, immobilizing its stinger and mandibles. This process is significant, as x-ray videography shows the ants remain alive for some time after being swallowed. The lizard's stomach is large, accounting for up to 13% of its total body mass, which allows it to consume the large number of ants—often over 100 per day needed for sustenance. A blood factor also appears to help neutralize any venom that does get injected.
Defense mechanisms and conservation
The Regal Horned Lizard has other unique biological traits. Its scientific name, Phrynosoma, means "toad-body," referring to its squat, flattened shape that helps it blend into the desert floor. This camouflage is the first line of defense. If threatened, particularly by canid predators like coyotes or foxes, the lizard employs a startling defense mechanism called ocular autohemorrhaging. It intentionally ruptures small capillaries in its eye sockets, forcefully squirting a stream of blood up to five feet away. The blood is laced with foul-tasting chemical compounds derived from the harvester ants it consumes, making it an effective deterrent.
The Regal Horned Lizard, along with the Texas Horned Lizard (Phrynosoma cornutum), faces significant conservation challenges. Since the 1960s, populations have declined sharply. The primary threats are habitat loss due to urban development and agriculture, the widespread use of pesticides, and the invasion of red imported fire ants. These invasive ants outcompete and destroy native harvester ant colonies, eliminating the lizard's primary food source. In Texas, the horned lizard is listed as a threatened species, making it illegal to capture or possess them. Conservation efforts, including captive breeding and reintroduction programs by organizations like the San Antonio Zoo, are underway to restore populations to their native habitats.