The San Antonio Zoo is teaming up with the Texas Parks and Wildlife Department in an effort to reintroduce the Texas horned lizard to parts of Central Texas and boost their numbers.

More commonly known as the horny toad or horned frog, Phrynosoma cornutum is the official reptile of Texas. The species has been listed as endangered by the state, though not federally listed, since 1977 and has become conspicuously absent from Texas scenery along with red harvester ants, the spiny reptiles’ main source of food.

“They used to be really abundant [in Central Texas], and for the last 30 or 40 years they’ve been basically extirpated,” said Andy Gluesenkamp, director of the San Antonio Zoo’s conservation and research department, in a phone interview Wednesday.

With public donations and a small grant from the TPWD Reptile and Amphibian Research and Conservation Fund, the zoo is establishing a captive colony –  Gluesenkamp calls it a “lizard factory” – to breed horned lizards and harvester ants for release into areas where their populations have dwindled in recent decades.

The lizard factory itself consists of an indoor, climate-controlled area with female lizards housed in individual terrariums with sand and full-spectrum light, surroundings that Gluesenkamp describes as “the lap of luxury for a horned lizard.” Eventually, the colony will be home to around 40 or 50 breeders. So far, one lizard brought in from the wild has laid a clutch of 33 eggs.

“We are hoping in the next year or so to start with reintroduction,” said Gluesenkamp, “producing hundreds of lizards per year and releasing the youngsters into the wild with the hopes of establishing a population there.”

TPWD created the Texas Horned Lizard Watch in 1997, where volunteers record lizard and ant sightings to estimate population densities in different counties around the state. A 10-year report issued in 2006 by the Horned Lizard Watch found that the lizard’s population decrease was most apparent in eastern regions of the state and along the Interstate Highway 35 corridor north from San Antonio. Populations are stronger in West Texas.

The report identified increases in urbanization, highway building, and intensive agriculture as factors that have contributed to changing and diminishing the horned lizard’s natural habitat of semi-arid expanses with scattered weeds and brush.

Another factor in the lizard’s dwindling numbers is the decrease in red harvester ants due to invasive fire ant migrations and the widespread use of pesticides to combat fire ants and other insects. Fire ants out-compete harvester ants for resources and are believed to attack harvesters directly, killing the queen ant to prevent new colonies from forming. Data from the Horned Lizard Watch shows that horned lizards are more likely to be in an area with harvester ants and less likely to be in an area in which fire ants are prevalent.

“The first step is to establish harvester ant colonies,” Gluesenkamp said, an effort that is continuing.

Several past attempts to reintroduce horned lizards to parts of Texas they had once inhabited have failed for reasons not fully understood, so the zoo is engaged in a collaborative effort with TPWD and researchers from Texas Christian University and Texas A&M University to determine the conditions that would best suit a fledgling horned lizard population, according to Gluesenkamp.

Despite their spiky and rugged outward appearance and the ability to shoot blood from their eyelids, horned lizards, especially hatchlings, find themselves the target of many predators like hawks, roadrunners, coyotes, and even mice.

“They’re pretty low on the food chain,” Gluesenkamp said. “I’m trying to go slowly, because you only get one chance [at reintroduction], and I want to do it right. But I’m fairly confident we will be able to succeed.”

In choosing locations to reintroduce the horned lizards, Glueskamp and his team will look for areas best suited for the reptiles to thrive and reproduce. The species prefers a semi-arid climate with sparse vegetation and sandy or loamy soil.

“Using detailed vegetation maps, we can create a suitability map for horned lizards based on plant communities and soil types in a given region,” Gluesenkamp said.

A suitable area would need to be 200 acres or more so that lizards could have room to disperse. Gluesenkamp identified Blanco County and Comal County as some of the first areas being scouted for intact ecosystems high in biodiversity and harvester ant populations.

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“We’re going to start working close to home,” Gluesenkamp said.“Just logistically, it needs to be a reasonable distance from [the San Antonio Zoo].”

Horned lizard eggs are close to hatching at the San Antonio Zoo.
Horned lizard eggs are close to hatching at the San Antonio Zoo. Credit: Bonnie Arbittier / Rivard Report

The Fort Worth Zoo has successfully bred horned lizards in captivity, and in 2010 started an ongoing reintroduction research project with TPWD. In 2014, TPWD wildlife biologists began work in the Muse Wildlife Management Area north of Brownwood in north Central Texas to gauge the feasibility of reintroducing horned lizards to areas further north and east. Preliminary findings from the Fort Worth Zoo and Muse WMA projects have been positive, fueling optimism for the possibility of more widespread reintroduction efforts.

“We’re hoping to see evidence of viable populations within a few years,” said Gluesenkamp, referring to the lizards’ relatively short lifespan of five to eight years and the fact that it takes two years for a horned lizard to reach reproductive maturity.

“It may take a sustained effort for a few seasons to keep that population going,” he added, noting the importance of public donations in sustaining the program.

“It’s exciting to me, because I spent seven years as the state herpetologist, and I think the most asked question was, ‘Are you going to bring back horned lizards?’ … It’s really important for people of my generation to be able to share these charismatic animals with younger generations, and this is a real opportunity to do that.”

Tom Bugg

Tom Bugg is a San Antonio native and student of English at Colorado College.