Dart, Stumpy, James Bond, Pancake, Mrs. Frizzle.
These are a handful of names assigned to the roughly 50 Texas horned lizards that bask under heat lamps, burrow into the sand and enjoy an endless supply of harvester ants at the San Antonio Zoo’s Center for Conservation and Research.
These spiky-bodied reptiles were once a common sight in and around San Antonio.
But their footprint has declined dramatically over the last several decades, especially in more developed areas like Bexar County.
Since 2020, the San Antonio Zoo has been actively breeding the lizards and releasing them onto a private ranch stocked with native plants in Blanco County, testing whether expanding such efforts could help the wild population sustain itself in the face of habitat loss and predation.
Over the last year, the zoo’s conservation team has rediscovered a handful of the camouflaged lizards they released years ago on the ranch, no easy task on the sprawling property.
And in May, the team came across a lizard whose black underbelly spots didn’t match any of their records, suggesting that it could be the first wild-born offspring of the San Antonio Zoo’s breed-and-release program — a significant mark of progress toward a self-sustaining population, if confirmed.
It will be several months, however, before researchers can trace the lizard’s lineage through genetic testing and rule out other possibilities.
In the meantime, keeping the lizards alive in the wild is a massive undertaking.
The lizard factory
Sporting a horned lizard tattoo on her arm, Bekky Muscher-Hodges presides over a room tucked away from the hustle and bustle of the zoo, what she and the team affectionately call “the lizard factory.”
Muscher-Hodges has been with the San Antonio Zoo for nearly 22 years.
For the last 10, she’s been in the conservation department working with the horned lizards.
Here, around 50 adult lizards are kept in heat-controlled enclosures. Next door, eggs are incubating. And baby lizards are kept upstairs in a separate nursery.
The San Antonio Zoo hosts one of several breed-and-release programs for the reptile in Texas.
Zoos in Fort Worth and Dallas, as well as researchers at Texas Christian University, maintain their own programs, releasing their lizards in Mason Mountain, a nature preserve in Central Texas.
Also referred to as “horny toads” for their wide frames, short snouts and protruding spikes, the Texas horned lizard is among 21 species of spiky-bodied reptiles native to North America.
The state is home to three distinct genetic clusters of Texas horned lizards that have adapted to their local environments: far west, including El Paso reaching into New Mexico and Mexico; southern, which includes San Antonio and South Texas; and northern, which includes the Dallas-Fort Worth area reaching into Oklahoma and Kansas.
The San Antonio Zoo is the only program that deals with reintroducing the southern cluster, which unlike its northern counterpart, doesn’t hibernate during the winter.
The lizard is an iconic symbol of Texas and the Southwest, and the beloved mascot of Texas Christian University. The largest populations can be found primarily in Texas, Oklahoma and New Mexico, but their range has decreased considerably over the last several decades.
During the warmer months, the lizards at the San Antonio Zoo undergo a “speed dating” process every few weeks, Muscher-Hodges said, since “arranged marriages don’t always work.”
Since the conservation team rarely catches the lizards “in the act,” they log every pairing and swab every animal, and genetic testing confirms paternity after the fact.
“Not that anyone’s paying child support here,” Muscher-Hodges added.
Tracking genetic lineages is important for other reasons: once released into the wild, the only reliable way to track the lizards is via genetic testing of the feces they leave on the property, which can be found much more easily than the camouflaged lizards themselves.
Every zoo-born lizard gets a cloacal swab before it’s sent off to the ranch, plus a photo of its black-spotted underbelly, which serves as a de-facto fingerprint.
The team refers back to this database later when they collect lizard scat, or spot the lizards themselves, at the ranch.
A vanishing icon
Texas horned lizards were once commonly spotted in and around Bexar County.
“You talk to folks my age and older that used to find these guys … they miss them,” said Muscher-Hodges, who is 51. “They would go out to Grandma’s house and pick them up, rub their bellies and stick them in a shoebox and keep them under the bed. You hear the same stories over and over and over again from people, just how much they love them.”
Increasing urbanization has fragmented the lizards’ habitats and displaced harvester ants, the staple of their diet. The destruction of native Texas vegetation has also made it more difficult for the species to avoid predation and forage effectively.
Overuse of pesticides and the introduction of invasive fire ants, which outcompete harvester ants and have been known to attack the lizards, have compounded these problems.
There isn’t good data on how much the population has dwindled, but it’s clear that their range has decreased considerably since at least the 1970s, especially in the rapidly developing eastern portion of Texas.
“The species has pretty much disappeared entirely on the eastern side of the I-35 corridor,” said Dean Williams, a TCU biologist who studies the animal and leads the lab that does the genetic testing of the lizards.
Williams’ lab helps track lineages and ensures that the lizards being reintroduced in the state are a part of the correct genetic clusters. The lab also makes sure the populations are diverse enough that inbreeding doesn’t occur.
Because there are still stable pockets of wild lizards, especially in West Texas and along the border, the species isn’t considered endangered.
Instead, they’re labeled as “threatened” in Texas, which makes it illegal to touch, pick up or keep them as pets without a special permit.
Everything eats them
Maintaining the lizard population is complex effort.
When the San Antonio conservation team travels to the ranch for surveys, they sometimes bring handheld vacuum cleaners filled with harvester ants that they sucked up elsewhere, plus a pressure steamer attached to a trailer to kill fire ant piles without using pesticides and containers to collect lizard scat that will eventually make its way to Williams’ lab.
They even used to bring specially trained dogs that could sniff out the lizards.
One fundamental challenge all the breed-and-release programs have struggled to overcome is that everything eats the lizards.
“Ox, owls, coyotes, snakes, skunks. … We lovingly refer to [horny toads] as nature’s popcorn,” Muscher-Hodges said.
Despite their spiky appearance, the lizards don’t have much in the way of defense — though they can squirt a stream of blood from their eyes at predators, a form of distraction more than protection.
“In the past it’s been really hard to do reintroduction programs with this species,” Williams said. The TCU research team has observed successful reproduction at the Mason Mountain site, but “not at the point where I would say it’s self-sustaining.”
“There’s been a few good nests that have hatched on those sites, and unfortunately, the females of those nests both got eaten by snakes by the end of that year,” Williams said.
The San Antonio Zoo’s conservation team estimates that the lizards survive 3-5 years on average in the wild, but a significant chunk of their offspring are eaten before they make it that far.
Another issue is their specialized diet: They rely on harvester ants for 70-90% of their energy and have evolved to avoid their venomous stings when chowing down on an ant pile. Although they can get more nutrients from larger insects available to them, they prefer the ants — so much so that they also tend to overeat them.
“They’re cute, they’re not smart,” Muscher-Hodges said.
The conservation team doesn’t have a great grasp on how many of the roughly 340 lizards they’ve released over the years are still alive.
But they have good reason to believe things are going well: every time they’ve traveled to the ranch this year, they’ve been able to spot a lizard instead of just scooping up scat.
Whenever the team finds a lizard, they refer back to their belly-spot database to see when the lizard was released. And all the scat they collect at the ranch goes to Williams’ lab. At least two different maternal lineages are surviving on the ranch, according to the latest genetic testing, Muscher-Hodges said.
One solution at this point would be to just breed and release more lizards, but the low hatch rate and fertility issues limit the number of lizards they can release.
When San Antonio Zoo researchers spotted a lizard that had a unique belly spot pattern in May, they celebrated what would be a first for the program: a wild-born lizard from one of its zoo-bred pairs.
It will be several months, however, before the zoo can prove it via genetic testing at Williams’ lab. An alternative explanation for the unique spots is that the lizard ventured in from a wild population elsewhere, or that it’s a dumped pet.
“The landowners went through a lot of trouble trying to rehabilitate that land to get it back to native Texas vegetation, proving that this is what these animals need to survive and thrive,” Muscher-Hodges said. “Having offspring is proof of them thriving and continuing that life cycle.”
A model for landowners
If the zoos and TCU researchers can overcome the challenges, the breed-and-release program could eventually become an offering for more landowners, which would serve as an incentive to bring in native grasses and improve the habitats on their ranches.
Other than the lizards being cute and iconic Texas symbols, they’re also an umbrella species for conservation efforts: sustaining their populations will inevitably result in conservation of a variety of other animals and plants, Williams said, like quail, roadrunners, shrikes and a variety of plants.
Regardless of the success of these programs, though, the population will likely not rebound in urban areas. The realistic goal is cultivating self-sustaining zoo-born pockets that can eventually be combined with wild populations to sustain their numbers.
“I don’t think it’s realistic to try to bring them back to where they once were,” Muscher-Hodges said. “There’s too much suburbia out there now. But [we hope] to get them in the spaces that are still wild or will be able to be rehabilitated back to that wild status, so that those numbers can be as plentiful in those spots as they were.”
