The Texas horned lizard can be easily distinguished from all other Oklahoma lizards by a combination of a short, squat body; two very large “horns” at the back of the head followed by two smaller ones on each side; a short, pointed tail; a distinct thin white line centered on the back and extending from the neck to the tip of the tail; and a double series of enlarged and pointed scales dividing the dorsal body surface from the ventral surface. The “horns” do not contain bone but are actually specialized body scales that serve to protect the lizards from predators Dorsal body color is variable, often red, brown, or gray, with irregular markings rendering the lizards cryptic against a variety of backgrounds. The belly is cream-colored. Males and females have few external differences except that males have visible pores along the lower hind surface of each thigh and a slight swelling at the base of the tail.
Texas horned lizards occur in all but the southeast corner of Oklahoma, but typically in open areas. Their North American distribution extends from southeastern Arizona east to south-central Arkansas and north from central Kansas south into Mexico. These lizards are adaptable to a wide range of conditions. As a general trend, horned lizards seem to be most common in habitats with sandy or loamy soils, and moderate grass or shrub cover.
Texas horned lizards are active in Oklahoma from early April through September. In October, they burrow underground to begin their winter hibernation. During the active season, they are usually found in open areas with sandy soil. Females deposit clutches of eggs (that vary in number with size of the female) in a slanted tunnel approximately 6-8 inches into the ground. Smaller females may produce clutches with more than 40 eggs. Hatching occurs in August, and hatchlings are about the size of a quarter when they emerge from eggs. The female provides no further care for her eggs or young and is not likely to lay more eggs that year. Individuals reach sexual maturity in the second year of life. Most of the diet consists of harvester ants; other insects such as beetles and spiders are eaten as well. Texas horned lizards lie motionless along harvester ant trails and capture ants as they pass to and from their colony. When an ant approaches, the lizard takes a few quick steps forward, flicks out its tongue, captures its prey and swallows it whole. Behavioral observations have shown that horned lizards may eat as many as 70 harvester ants a day. Horned lizards usually attack solitary ants several yards away from the harvester ant colony, and avoid the colony’s center where they would be mobbed by droves of biting ants. Avoiding predators influences many of the Texas horned lizard’s behavioral and physical adaptations. Though capable of running quickly for short distances, they rely more on camouflage than speed for protection. Their first line of defense is their mottled brown body coloration that helps hide them against bare soil and dead leaves. For further camouflage, local populations tend to resemble the color of their area’s soil. Populations in areas of sandy soil may have a yellowish tint while populations in other areas may have a reddish or dark brown tint. The body shape is also an adaptation to avoid the attention of would-be predators. When lying against the soil, the flattened body casts only a slight shadow, and the spines on the back and sides help break up the body’s outline. A motionless horned lizard is difficult to see against bare soil. Texas horned lizards (and some other species of horned lizards) have a fascinating behavior used to detract predators. When grasped, they close their eyes and the eyelids appear to inflate. They then squirt a directed stream of blood from the sinuses in their eye cavity toward the would-be predator. Experiments have shown that the blood is distasteful and repels some predators, canids (coyotes) in particular. Chemicals in the blood that produce the bitter taste may be derived from the ants they eat. Little information is available on their normal lifespan, but horned lizards can live at least five years.
Adult females reach about 5 inches in snout-vent length, but males are smaller, reaching only about 3.7 inches. Recently hatched juveniles are about three-quarters of an inch in snout-vent length.
The Texas horned lizard remains common in parts of western Oklahoma, but since the 1960’s has shown a dramatic decline in both range and population size in the eastern and central parts of the state. Several possible reasons have been proposed for the decline, but little evidence exists to determine the true causes. The horned lizard’s decline is most likely the result of a combination of factors with the importance of each factor varying from one part of the state to the next.
• As native habitats are modified by human development, some areas may no longer be suitable for horned lizards or their harvester ant prey. With less suitable habitat, fewer lizards can be supported. Also, as the amount of habitat declines, the remaining patches of good habitat become more isolated from each other. Because of their small size and limited ability to travel long distances, horned lizards have difficulty moving between widely spaced habitat patches. Populations in isolated habitats are more susceptible to local extinction from catastrophic events, and once an isolated population is gone, it is difficult for other horned lizards to resettle the area.
• Increased use of pesticides may have reduced the harvester ant population in some areas, thus reducing the horned lizard’s main food supply. In agricultural areas, ants are rarely considered pest species but may be killed by insecticides used against other insects. Also, herbicides used to eliminate weeds may affect harvester ant populations by reducing the abundance or quality of seeds on which the ants feed. In residential areas, ants are often poisoned by people fearing ant bites or wanting to keep them away from stored food. Because harvester ant colonies are easily visible, these harmless ants are often destroyed.
• Prolonged periods of hot, dry weather associated with extreme drought may cause harvester ants to go dormant and temporarily eliminate the lizard’s most important food source. A severe drought hit Oklahoma in the early 1980’s and may have caused some of the decline.
• Because horned lizards may lie on roads to bask on the warm pavement or gravel, they are vulnerable to vehicle kills. As the number of roads and vehicles increase, the probability that horned lizards will be hit and killed increases.
• In some areas, the number of potential predators on horned lizards may be higher now than in the past. Though little evidence has measured the effect of predation on horned lizard populations, increased populations of possible predators such as feral cats, cattle egrets and great-tailed grackles have been suggested in recent years, especially around towns and pastures.
• The collection of horned lizards as pets or to sell commercially in the pet trade may have affected some populations, especially near towns and cities. Anecdotal accounts state that thousands of horned lizards were shipped out of Oklahoma and Texas and sold for pets in the eastern U.S. and Europe from the early 1900’s until the 1980’s. Because of their special diet, most of these lizards died from improper care within a few weeks, and no self-sustaining captive-bred populations were ever developed. Horned lizards are now protected in Oklahoma and Texas and this activity is illegal. However, where collecting was common, some populations may not have recovered yet.
Species of Greatest Conservation Need
Species of Special Concern