As of 1987, Texas ranked first among the fifty states in numbers of reptilian species, with thirty-five species of turtles, sixty-one of lizards, sixty-eight of snakes, and the American alligator. This abundance results from the diversity of habitats within the state and its location in a region where four distinctive biogeographic regions meet, loosely described as eastern, desert, High Plains, and subtropical. Five species (two turtles, two lizards, and the Harter's watersnake) fit none of these categories.
The turtle fauna, which is dominated by freshwater forms, is richest in eastern Texas. Six saltwater species, five sea turtles and the diamondback terrapin, also occur on the Texas coast. Of these perhaps the best known is the Kemp's Ridley turtle. The ornate box turtle (Terrapene ornata ornata) is the common land turtle over most of the state. This species, which perishes by untold hundreds each year on the state's highways, is a frequent backyard pet. The only true tortoise in the state is the Texas tortoise (Gopherus berlandieri), a species that ranges into southern Texas from Mexico and is on the list of threatened species and thus protected by state law.
The American alligator (Alligator mississippiensis) at one time was widely distributed over the eastern part of the state; sightings were recorded as far west as Dallas, Austin, and San Antonio. Today, spotty breeding populations are confined to eastern Texas east of the Trinity River and to coastal areas; rare sightings occur along the Colorado River. Although the species at one time was severely threatened, protection under state and federal law has led to an increase of 50 percent in numbers (almost 70,000 in 1980), so that limited harvest has been permitted.
Lizards are well represented throughout the state, although the greatest diversity occurs in the west. Certainly the most popular of all Texas reptiles is the Texas horned lizard (horned "toad"), Phrynosoma cornutum, one of the three species of horned lizards in the state. The favored food of this little reptile consists of ants, especially harvester (red) ants, although it may eat other insects, especially beetles. Habitat destruction, collecting, and, probably, pesticide use, have led to a decline of the Texas horned lizard in many parts of the state, and the species is now classified as threatened and protected under state law. The most ubiquitous and widely distributed Texas lizard is the Southern prairie lizard, Sceloporus undulatus consobrinus, a little spiny lizard with arboreal tendencies in the east but with ground-living habits in the west. Other conspicuous lizards in the western part of the state include the Great Plains skink (Eumeces obsoletus), the collared lizard (Crotaphytus collaris), and various species of whiptails (Cnemidophorus), several of which are unisexual.
Fifteen of the sixty-eight species of snakes in Texas are poisonous. These include the coral snake (Micrurus fulvius tenere), western cottonmouth (Agkistrodon piscivorus leucostoma), three copperhead species (Agkistrodon), and ten rattlesnakes. The first three of these species, together with two rattlesnakes, are essentially East Texas forms, although the coral snake and cottonmouth both range westward onto the Edwards Plateau and the copperhead occurs as far west as the Davis Mountains. Certainly the most infamous of Texas snakes is the western diamondback rattlesnake (Crotalus atrox). This large, dangerous snake occurs over three-quarters of the state, is responsible for over half the cases of poisonous snakebite, and is the culprit in almost all instances of death due to snakebite in Texas. A rich folklore has grown up around this snake, much of which was recorded by J. Frank Dobie in his book Rattlesnakes (1966).
Resource collections of state reptiles include the Texas Natural History Collection (Texas Memorial Museum , Austin), the Texas Cooperative Wildlife Collection (Texas A&M University), and the collection of the Strecker Museum (Baylor University). The Texas Herpetological Society, founded in 1939, includes amateur and professional students of amphibians and reptiles and is the oldest state society of its kind in the United States. As of 1988 the following turtles were classified by the Texas Department of Parks and Wildlife as endangered: loggerhead, Atlantic hawksbill, Kemp's Ridley, leatherneck, and Big Bend mud. No lizards were classified as endangered, but five snakes were: the speckled racer, Louisiana pine snake, Concho water snake, western smooth green snake, and northern cat-eyed snake. See also MOCCASINS.