Texas Wildlife (July 2011)
By
Henry Chappell
Nobody would call a Texas Horned Lizard pretty. Cute, perhaps, in the inexplicable way of an ostrich, ladybug, or baby snake.
In “Jimmy Hayes and Muriel,” a story about a young Texas Ranger and his beloved pet horned lizard, O. Henry describes “Muriel”:
“The stumpy little lizard known as the horned frog is harmless. He has the hideousness of the prehistoric monsters whose reduced descendant he is, but he is gentler than the dove.”
Hideousness? I prefer “character.” I suspect that students, alumni, and fans of a certain university in Fort Worth, one whose football team was, in my opinion, the best in the nation last season, would agree.
We know him as the horny toad or horned frog, but he’s not an amphibian. As his name suggests, the Texas Horned Lizard is a reptile, the official reptile of the State of Texas, in fact.
In Biological Survey of Texas, 1889-1905, in the section devoted to lizards, chief naturalist Vernon Bailey called the “Horned Toad” the “commonest and longest-horned species of Texas horned toads.” Describing specimens collected from across the state, he notes a gradual darkening in color from the “lightest and brightest” specimens in the Upper Rio Grande Valley to the darkest at Virginia Point and Antioch in East Texas. The lighter western specimens had narrow face bands and white bellies. The darker eastern horned lizards sported “sharply marked face bars and gray, thickly spotted bellies.”
More generally, the Texas horned lizard’s color ranges from gray to brown to rust, with rows of dark spots down the back, a light central stripe, and dark bars radiating like spokes from the bottom half of the eye. Two prominent horns, rise from the back of the skull, roughly equidistant from a tiny center nub. Body length varies from about 3.5 inches to 5 inches. Two rows of spiky scales run along the sides. The body is flat and nearly as wide as long.
The scientific name of the horned lizard genus, Phrynosoma, means “toad-body.”
Two other horned lizard species live in Texas: the Round-Tailed Horned Lizard, which has four medium length horns and is restricted to the rocky western third of the state, and the Greater Short-Horned Lizard of the high elevations of the Davis and Guadalupe Mountains.
Texas horned lizards prefer flat, open terrain, and sandy or sandy loam soil with sparse vegetation, although their historical range includes portions of East Texas where they had to contend with thicker cover. Horned lizards dig shallow burrows or depressions, but also use mammal burrows. Vegetation clumps, and rock piles serve as protective cover. A horned lizard’s home range can be as large as 6 acres. There’s very little overlap among home territories of adults.
Harvester ants make up the bulk of the horned lizard diet, a fact that partly explains the lizards’ preference for bare ground. These large red ants clear vegetation around their mounds, which are easily identified by scatterings of small pebbles dug from within the nest. An abundance of horned lizard scat – symmetrical, oblong pellets ½ inch to 1 ½ inches long and containing ant body parts - is a dead giveaway. Termites, other native ants and insects, spiders, and sowbugs round out the horned lizard’s diet. Unfortunately, they don’t eat fire ants.
Horned lizards like hot weather. They’ll often start their day by poking their heads out of the sand while leaving their bodies submerged until the surface warms enough to stimulate appetite and make for comfortable hunting. In general, horned lizards are inactive at night and anytime temperatures fall below 75° F. During fall and winter, they hibernate a few inches underground.
The lizards mate in spring, shortly after they emerge from hibernation. The female digs a hole 6 to 8 inches deep and lays 13 to 50 eggs which rely on soil warmth for incubation. Baby horned lizards about ¾-inch in length begin to hatch 5 to 9 weeks later, depending on soil temperature.
Despite their fierce appearance, everything eats horned lizards. Snakes, coyotes, foxes, raccoons, hawks, roadrunners , feral dogs and cats – just about every local mammalian or avian predator. Nevertheless, due mostly to their near-perfect camouflage, tendency to lie perfectly still or dart into cover, they may live 5 to 8 years – a long time for a wild animal.
Left with nowhere to hide, horned lizards aren’t helpless. They’ll sometimes bluff by puffing up like a spiny balloon . The tactic might intimidate a small predator but doesn’t deter an annoying wildlife photographer.
Laurie Hall, who shot the photos for this article, described an encounter with a belligerent horny toad on the Rolling Plains near Vernon. “He’d stand still for me for a while, then he’d take off like a rocket for some kind of cover,” she said. “They can move amazingly fast. I was trying to coax him out of this clump of grass and he started puffing up. He’d blow himself up on one side and flatten out on the other side. A little later, when he was out in the open, and I got a little too close with the camera, he actually jumped at me. I had never seen that before.”
Texas horned lizards (and short-horned lizards) reserve their most gruesome countermeasure for canine predators. Under dire threat, a lizard may squirt a stream of blood from ruptured blood vessels in the sinuses near the eye. Canines find a chemical in the blood distasteful.
Historically, Texas Horned Lizards inhabited most of the state with the exception of deep East Texas. Studies and anecdotal data suggest that horned lizards have declined over much of their range, though they remain relatively abundant over much of South Texas, the Rolling Plains, High Plains, and Trans-Pecos ecoregions. They’re also fairly abundant in sandy areas within the Post Oak Savannah ecoregion.
The lizards seem to be in serious decline in parts of Central Texas, especially in the I-35 corridor north of San Antonio, and are apparently rare in the Coastal Prairie region. Although they were likely never abundant in the Pineywoods, and data are scarce, horned lizards have likely declined or disappeared over most of the region.
Horned lizard populations have declined in North Texas, especially in the Blackland Prairie region where intensive agriculture and urbanization have radically altered the landscape. Surprisingly however, volunteers with Texas Horned Lizard Watch reported 15 sightings in highly-urbanized Dallas and Tarrant counties between 1996 and 2006.
The decline has been attributed to habitat loss, collection for the pet trade, and the spread of imported fire ants. Over-collection led Texas Parks and Wildlife Department to list the Texas Horned Lizard as threatened in 1977. Data collected by Texas Horned Lizard Watch show a marked negative relationship between the presence of fire ants and horned lizard sightings in some parts of the state.
Texas Parks & Wildlife biologist Nathan Rains suspects a combination of factors.
“If it were only one thing, we’d figure it out,” he said. “For example fire ants complicate things because they out-compete and displace harvester ants, and if they find a horned lizard nest, they’ll destroy the eggs, but they’re not the only problem. Fire ants and horned lizards co-exist in South Texas. In North Texas, they’re one more problem faced by a population already stressed by habitat fragmentation. In addition to a growing human population and development, we’ve had a lot of pasture converted to coastal Bermuda, and the lizards just can’t navigate the stuff.”
Over the next year, Rains and his colleagues will be studying the feasibility of releasing captive-bred Texas Horned Lizards on previously occupied habitat in Parker County. The researchers will release several lizards bred at the Fort Worth Zoo and fitted with micro-transmitters into a 10-foot square protective acclimation pen located in suitable habitat – a process known as a “soft release.” After a few weeks of acclimation, the enclosure will be enlarged. Eventually, the lizards will be released into the pasture and tracked with telemetry equipment.
“We’ll be looking at survival and dispersal mainly, and maybe reproduction if the transmitter batteries last long enough,” Rains said.
While captive-bred horned lizards might someday augment wild populations, no amount of relocation and release can overcome lack of habitat. Texas Parks & Wildlife and other agencies and organizations can do their part on public lands such as wildlife management areas, refuges, and parks, but in Texas, where 97 percent of land is privately property, real recovery depends on landowners.
In "Management of Texas Horned Lizards," Scott E. Henke and Wm. Scott Fair of the Caesar Kleberg Wildlife Research Institute of Texas A&M University – Kingsville offer guidelines for landowners interested in conserving and increasing horned lizard populations on their properties. In general, these are consistent with sound range management and may benefit other species such as bobwhite quail and other grassland birds.
Key among these guidelines is maintenance of a diversity of native plant species. Diverse plant communities attract a variety of invertebrates which can be especially important to juvenile horned lizards. Bunch grasses such as bluestems, and native forbs, allow for easy foraging whereas many domestic grasses produce a thick carpet that inhibits movement. Native grass seeds provide food for harvester ants.
While native plant communities tend to provide the patchwork of cover and open ground that horned lizards require, judicious grazing, mowing, and prescribed burning can create, enhance and maintain habitat. Ideal horned lizard habitat consists of a mosaic of bare ground, native grasses, and brushy cover. Clearing spots of about a square yard provides basking areas for horned lizards and colony sites for newly fertilized harvester ant queens.
Moderate grazing is good range practice and can actually increase plant diversity under some conditions. In contrast, heavy stocking reduces necessary cover and may contribute directly to horned lizard mortality.
Broadcast pesticides can kill harvester ants and other valuable insects and may kill lizards directly.
Horned lizards use unpaved ranch and farm roads for resting and bedding sites. Where practical, grading of secondary roads should be restricted to the horned lizard’s inactive seasons. Driving speeds should be limited during morning and late afternoon during spring, summer, and early fall. Easing along secondary roads during periods of peak horned lizard activity can be an excellent way to survey populations.
You needn’t be a landowner or biologist to help horned lizards. Since 1996, volunteers with Texas Horned Lizard Watch have provided Texas Parks & Wildlife department with valuable survey data.
Oddly charismatic yet small and retiring, Texas Horned Lizards go about their business mostly unnoticed by humans. We should pay attention lest we look down one day and find them gone.
ADDITIONAL INFORMATION
As a threatened species, Texas Horned Lizards may not be collected or handled without proper authorization. Contact Texas Parks and Wildlife Department for details – www.tpwd.state.tx.us
Further Reading
"Management of Texas Horned Lizards" by Scott Henke and Wm. Scott Fair (1998, Caesar Kleberg Wildlife Research Institute) - http://ckwri.tamuk.edu/fileadmin/user_upload/docs/bulletins/bulletin2.pdf
Horned Lizards by Jane Manaster (2002, Texas Tech University Press) - http://ttupress.org/
Get Involved
Texas Horned Lizard Watch - http://www.tpwd.state.tx.us/learning/texas_nature_trackers/horned_lizard/
Horned Lizard Conservation Society - http://www.hornedlizards.org/index.html
