Center for Conservation & Research

at the San Antonio Zoo:

Texas Horned Lizard Reintroduction

Texan by Nature (TxN) selected the Center for Conservation and Research (CCR) at San Antonio Zoo Texas Horned Lizard Reintroduction project as a 2021 Conservation Wrangler for its positive impacts on people, prosperity, and natural resources. The Center for Conservation and Research (CCR) at San Antonio Zoo Texas Horned Lizard Reintroduction Project seeks to restore the Texas horned lizard population by working with private landowners to introduce zoo hatched lizards in areas where it has disappeared in recent decades. CCR assesses candidate release sites based on several criteria using remote habitat ranking and boots-on-the-ground surveys. In addition, CCR provides management guidance and assistance to landowners who wish to manage their property for native biodiversity, including horned lizards. 

Through the Conservation Wrangler program, TxN is helping San Antonio Zoo to connect with individual partners and conservation organizations that are working towards the conservation of Texas horned lizards across the state. Texan by Nature aims to help CCR replicate the Texas Horned Lizard Reintroduction project model through sharing best practices, case studies, and habitat management guides to encourage statewide science-based horned lizard conservation efforts among landowners, businesses, and environmental groups.

What is the Texas horned lizard?

The Texas horned lizard (Phrynosoma cornutum) is one of fourteen species of horned lizards distributed from Southern Canada to Southern Mexico. Common names include “horned frog” or “horny toad”, but they are actually reptiles, not amphibians. The scientific name Phrynosoma means “toad-body” and cornutum means “horned.” This beloved reptile species has been recognized as the state reptile of Texas since 1993, and is listed as threatened at the state level.

The Texas horned lizard measures three to five inches long, and is characterized by five long sharp horns that crown its head, and two rows of enlarged pointed scales that line its short, plump body. Horned lizards are dietary specialists, feeding predominantly on red harvester ants (Pogonomyrmex), found throughout the majority of their habitat range. These reptiles have adapted a sticky tongue that is specialized to catch ants quickly and effectively, and have even developed a resilience to most ant bite toxins. 

The Texas horned lizard has additional unique adaptations that allow it to survive in harsh arid desert environments. Due to living in grasslands and deserts with little water, the lizards exhibit specialized skin adaptations that allow them to access water from sources such as moist sand and dew. The rough scales of the horned lizard are capable of collecting water and transporting it directionally through a capillary system between the scales. This fluid transport is passive, requiring no external energy, and directs the collected water towards the lizard’s mouth. This specialized water acquisition strategy allows the horned lizard to save energy that would be spent on finding water, and utilize it for things like mating, foraging, and predator defense. 

Texas horned lizard predator defense

The predator defense mechanisms of the Texas horned lizard are quite extraordinary. Initially, the animal exhibits cryptic coloration, or camouflage, to deter predators from noticing them. The morphology of the Texas horned lizard is flat, but when there is a perceived threat, the animal can “puff up” its body, causing its spines to protrude. This makes it more difficult for a predator to eat the lizard. When threatened, the animals also have the ability to shoot blood out of tissues in the eye socket, which causes the predator to retreat. Although Texas horned lizards are prey to many species such as snakes and birds, blood-squirting is the most effective chemical defense in predator-prey encounters with wild canids, such as coyotes.

The Texas horned lizard once ranged from the south-central United States, down to northern Mexico, and throughout much of Texas, Oklahoma, Kansas and New Mexico. These reptiles could once be found in such high abundance, that it wasn’t until the 1970’s that people began to notice their populations were in a steady decline. This map shows the extant region (depicted by red dots) where the Texas horned lizard was once present, across a wide part of central North America.

Map showing historic distribution(green/yellow) and current population range(red) of Phrynosoma cornutum.

The historic distribution of the Texas horned lizard has shrunk significantly in the past 20 years. The state reptile could once be easily found throughout most of Texas, and is now nearly extirpated from the Eastern third of the state. In Texas, the horned lizard has disappeared from at least 30 percent of its historic range (depicted by green/yellow in the image above), mostly in the central and eastern portions of the state. In this map, you can see that the Texas horned lizard is now observed much less in the Eastern side of the state than in the Western side.

Why did the population decline?

There are many factors threatening the distribution of Texas Horned Lizards- invasive species, habitat loss, and pet trade being some of the most impactful. The biggest horned lizard population crash we’ve seen in Texas happened between the late 1960’s and early 1970’s, when the reptiles were met with the impacts of a new invasive species.

Invasive species:

Red imported fire ant (Solenopsis invicta)

The most problematic invasive species to the Texas Horned Lizard population is the red imported fire ant (Solenopsis invicta). These South American ants were accidentally introduced to the U.S. in the 1930’s via cargo ships entering Mobile, Alabama. Since then, these voracious insects have now spread to more than 320 million acres across fifteen states. The invasive ants overtake the population of native Harvester ants, reducing the amount of food available for horned lizards to eat. This is because red imported fire ants often become the dominant ant species in areas outside of their native range due to their aggressive foraging behavior, high reproductive capability and lack of predators and/or other strong competitors. Texas horned lizards are unable to consume the red fire ants, and have been known to attack vulnerable horned lizard hatchlings. Because of this, horned lizards will flee an area where the invasive species is present.

Habitat fragmentation and loss:

The urbanization of rural areas in Texas lowers the amount of grassland and desert habitat available for the reptiles to survive. For example, horned lizards don’t do very well in long grass, like the St. Augustine species which many people use to sod their lawns. Urbanization also contributes to habitat fragmentation, creating smaller isolated populations of Texas Horned Lizards that are more susceptible to population pressures. Although it’s tough to point to a single cause of the disappearance of the Texas horned lizard, it’s clear that the more modified their native habitats become, the less they are able to survive and reproduce. Much like most other wildlife species, they also don’t have very good luck with paved roads. Horned lizards often fall victim to moving vehicles, and the number of highway miles in Texas has increased exponentially from 35,000 miles to over 79,000 miles since 1935.

Pet trade:

Young girl with her pet horned lizard, 1936

The illegal pet trade puts major stress on the already-struggling population of Texas horned lizards. Although they are listed as protected in the state of Texas, the species can still be found in pet stores as far away as New Jersey. It is challenging to provide these reptiles with appropriate care as pets, as they are so uniquely specialized for their desert environment. Because of this, many Texas horned lizards that are kept as pets do not survive for very long outside of their natural habitat.

What is the Center for Conservation and Research at San Antonio Zoo doing to help the Texas horned lizard?

The Center for Conservation and Research (CCR) at San Antonio Zoo Texas Horned Lizard Reintroduction Project seeks to restore the Texas horned lizard population by working with private landowners to introduce zoo hatched lizards in areas where it has disappeared in recent decades. CCR assesses candidate release sites based on several criteria using remote habitat ranking and boots-on-the-ground surveys. In addition, CCR provides management guidance and assistance to landowners who wish to manage their property for native biodiversity, including horned lizards. 

Establishment of viable horned lizard populations requires the production of large numbers of lizard hatchlings from CCR’s “Lizard Lab.” The lab is a 450-square foot room, and former receiving bay of the zoo’s warehouse that has been modified to include two sets of timer-controlled power outlets (one for UV lights and one for basking lights) and heavily-insulated exterior walls. This lab houses all breeder adults, and seasonally serves as the “Lizard Nursery” for hatchling lizards.

L: CCR “Lizard Lab”, R: A Texas horned lizard eats a Red Harvester Ant in the “Lizard Lab”

The young lizards hatched in the “Lizard Lab” are introduced to the release site in early fall, and the property is monitored for horned lizard activity at regular intervals. CCR has partnered with Paul Bunker, owner of Chiron K9, to develop the Horned Lizard Detection Canine Network, a group of volunteer handlers and their canines who are trained to seek out horned lizards. Dogs are scent trained with live horned lizards, scat, eggs, and shed skin so that they may detect any traces of Texas horned lizards in the field. This partnership with Chiron K9 provides CCR with an efficient long term method for monitoring lizards post-release, and helps to ensure the overall success of the project.

L: Horned Lizard Detection K9 Network team, R: Detection K9 “Gren” finds horned lizard scat

By re-establishing horned lizard populations and encouraging voluntary management that benefits native biodiversity, CCR hopes to not only improve native biodiversity across Texas, but also promote awareness and appreciation of this species for the benefit and enjoyment of present and future generations. CCR’s long-term project goal is to develop replicable methodologies to share with other conservation entities, to ultimately ensure the return of this beloved species to places where its absence is so deeply felt.

What can I do to help the Texas Horned Lizard?

Become a citizen scientist
iNaturalist is an online community of naturalists, citizen scientists, and biologists built on the concept of mapping and sharing observations of biodiversity across the globe. With over one million registered users, this platform serves as a comprehensive database that tracks global plant and wildlife biodiversity and abundance. You can help the conservation of threatened and endangered species like the Texas horned lizard by creating an iNaturalist account to record your observations. If you come across Texas horned lizard scat, shed skin, or even tracks in the wild, take a photo and upload your findings to the online platform. By keeping a public record of sightings, wildlife biologists are able to better determine the most accurate and up-to-date population distribution of the species.

Let wildlife stay wild
Because the Texas horned lizard is listed as a threatened species, it is illegal to pick up, touch, or possess them in Texas. Handling horned lizards is illegal, and even if your intentions are good, you are in violation of the law and could be ticketed for your actions. Scientists are required to obtain scientific research permits from the Texas Parks and Wildlife Department prior to conducting research on horned lizards (TPWD: Wildlife Diversity Permits: Scientific Permits for Research).

Spread the word

Collecting harvester ants at a San Antonio Zoo “Ed-ZOO-cation” event

Through educating the American population on the plight of the Texas horned lizard, we can provide these reptiles with safe and supportive habitats to sustain healthy populations. Education is crucial to get Texans excited about their state reptile, and spreading the word of horned lizard conservation across the state! At San Antonio Zoo, the general public has the opportunity to see these animals during hands-on Ed-ZOO-cation events, and learn more about their history in and around Texas. By learning about the Texas horned lizard and sharing your knowledge with the world, you are acting as an advocate for the species, perpetuating a lasting spirit of conservation for future generations.

Manage your backyard
By taking simple steps to take care of your backyard in a sustainable way- like reducing pesticide use, planting native landscaping, and removing invasive species- you can make your land more friendly for horned lizards and other native species. These steps do not necessarily guarantee that horned lizards will return to your property, but sustainable land management practices help a variety of different native species, such as birds and pollinators. Additionally, applying conservation practices in your backyard can save you money through water conservation.


  • Treat fire ant mounds without the use of pesticides. Fire ants are a common resident in suburban neighborhoods, and management without the use of pesticides is imperative in maintaining a healthy ecosystem. Individually treat each mound, drowning the area with a bucket of very hot water and a bit of dish soap, digging the water in with a shovel.
  • Spay and neuter your pets, and supervise them outdoors. Another group of invasive animals that can negatively impact the population of horned lizards are feral domesticated dogs and cats. When left outside without supervision, these pets prey upon the docile reptiles in residential and urban areas, reducing the amount of safe habitat available to the lizards. Contact your local Humane Society for assistance in removing these feral domesticated predators.
  • Landscape your yard using native plants instead of nonnative plants. Native plants improve soil health, attract native pollinators, and even conserve water- saving you money!

Additional Landowner Resources

If you are a landowner, and would like to learn more about management strategies for Texas horned lizards, please refer to the following resources:

  • The Texan by Nature Landowner Guide is a comprehensive list of state, federal, and NGO programs for conservation restoration, as well as resources for project planning and recognition for your efforts. 
  • The Caesar KIeberg Wildlife Research Institute at Texas A&M Kingsville Management of Texas Horned Lizards bulletin outlines the ecology and habitat requirements of the Texas Horned Lizard, and management practices are suggested that should benefit the species. 
  • The Texas Parks and Wildlife Department Texas Horned Lizard Management and Monitoring packet is a product of the Texas Horned Lizard Watch program, created to encourage volunteers to participate in horned lizard data collection and research.

Learn more about the Center for Conservation and Research at San Antonio Zoo’s Texas Horned Lizard Restoration efforts here: 

If you are interested in supporting Texas horned lizard reintroduction as a landowner, please fill out this brief survey so that CCR can determine if your land meets the Texas horned lizard reintroduction habitat requirements.