Texas has some ten rattlesnake species and subspecies, more than any other state except Arizona. Only three species interact significantly with human beings, however-the western diamondback (Crotalus atrox), the prairie (C. viridus viridus), and the eastern timber or canebrake (C. horridus atricaudatus). These species are widely distributed, are comparatively large, and often exhibit an aggressive temperament. The western diamondback (atrox denotes "frightful" or "grim") accounts for nearly all the state's serious cases of venom poisoning. The venom of all three species contains both neurotoxically active peptide components and a larger complement of enzymatic fractions that destroy blood and tissue. Diamondback venom has more of the latter as well as about a third greater overall potency than the toxins of either C. viridus or C. horridus.
The primary functions of rattlesnake venom are to kill and predigest food animals, a process that starts with the metabolic dissolution of the victim's tissues well before the creature is swallowed. Humans bitten by rattlesnakes and other pit vipers experience immediate severe pain, swelling, sweating and chills, faintness or dizziness, elevation of pulse rate, vomiting, and enlargement of the lymph nodes near the bite. The fang wounds should never be cut open, since the venom proteins so quickly bond to those of their host that extracting them, either in the field or the hospital, is nearly impossible. Instead, the limb should simply be wrapped in a splinted elastic bandage to compress the lymph system that spreads most of the venom. Because the dispersal of the toxins occurs very gradually, there is ordinarily a period of hours in which to obtain hospital treatment, and only a heavily envenomated small child (whose body-fluid volume could be too low to accommodate the plasma leakage brought about by the venom's perforation of capillaries) would require the temporary application of a tourniquet above the bite. Few people die from rattlesnake poisoning-less than 10 percent of even those heavily envenomated, mostly the very young or people in poor health. Peripheral morbidity, including the loss of digits and even limbs, is high and is often aggravated by ill-advised popular first-aid procedures. Many unfortunate encounters with rattlesnakes occur around rural outbuildings where the snakes seek prey animals; other bites occur when rattlers sheltering beneath piles of unused lumber or, on the coastal islands, driftwood, are accidentally uncovered. Ground-nesting birds are a favorite prey of most rattlesnakes, although two small species, the pygmy rattler and the rock rattler, eat mostly cold-blooded animals; insects, amphibians, and smaller reptiles are the pygmy's frequent prey, lizards that of the rock rattler. The smaller western and desert rattlers, the massasaugas, also take cold-blooded vertebrates. When prey is plentiful, rattlesnakes feed heavily and build up fat reserves that both support them through months of cold weather and enable the females to forego hunting during the latter stages of pregnancy. In prime conditions the young grow rapidly and shed their old skins every six to twelve weeks. With each shed a new segment is added to the base of the rattle-replacing the terminal sections that periodically break off like a too-long fingernail. The length of a snake's rattle is no indication of its age.
In Texas, breeding takes place both in spring and fall, when members of communally denning species such as the prairie and diamondback rattlers are found in closest proximity (during the summer they are dispersed over wide feeding ranges). The young are born alive in early autumn, at which time newborns may appear in considerable numbers, searching for the prey they must find promptly in order to survive their impending hibernation. A few adult diamondbacks are abroad during warm spells throughout the winter in the southern part of the state, but they remain near their dens and feed infrequently until spring. The dorsal ground color of the western diamondback varies from yellowish or pinkish tan to dark gray brown, with or without the white-edged vertebral diamonds for which the snake is named. Its tail is distinctly banded with black and white. Except in the Panhandle and in some areas of the Hill Country, the diamondback is the most numerous venomous snake in the western two-thirds of the state. It is also the largest, although its large size is a topic of controversy since snakes and snakeskins are often stretched up to 25 percent after death. A few C. atrox close to 7½ feet long, not counting the rattle, have come from the area of Starr County in the Rio Grande valley; despite constant reports to the contrary it is unlikely that any is larger.
The prairie rattler is a slender, medium-sized snake that lives predominantly in the Panhandle grasslands and sometimes in the Trans-Pecos. The dark-edged, rounded, brown vertebral blotches on its forebody lengthen on the posterior trunk into transverse crossbars; its tail is banded with brown and tan.
The timber or canebrake rattler is a big, dark-tailed rattlesnake that favors densely vegetated habitats in the eastern part of the state. With dark brown dorsolateral chevrons and a rusty vertebral stripe on a pinkish-beige ground hue, it is so differently colored from the so-called northern timber rattler that it may constitute a separate race, C. atricaudatus.
The northern blacktail (C. molossus molossus), the "green," "velvet-tail," or "dog-faced" rattler of the wooded canyons and mountains of West Texas, sometimes displays an olive cast but is more often brown or silvery gray. Besides its uniformly sooty tail (ahead of the rattle), the blacktail has a dark mask, and along the spine a wide, blackish-brown stripe encloses patches of pale scales. The Mojave rattlesnake (C. scutulatus scutulatus), a predominantly Mexican viper, ranges northward into Texas primarily along the Rio Grande west of the Big Bend. The venom of Arizona populations may be several times as powerful as that of the western diamondback, from which the Mojave is distinguished by the two or three rows of enlarged scales that line the center of its forecrown (diamondbacks have four or more rows of much smaller scales in this area).
Mottled rock rattlesnakes (C. lepidus lepidus) are often common in broken desert, canyon, and evergreen mountain terrain. The species has evolved dorsal coloring that substantially matches the prevailing hues of its background terrain-pinkish on the russet igneous boulders of the Davis Mountains, pale gray on the chalky limestone of the central Hill Country and southwestern deserts. The banded rock rattlesnake (C. l. klauberi), named for a noted authority on rattlesnakes, Lawrence M. Klauber, is a distinctly black-crossbanded subspecies found primarily in the two westernmost counties of Texas, but it has been reported in Val Verde County as well. Because of their unusual pigmentation both races of rock rattlers are attractive to reptile fanciers and are therefore protected from capture by state law.
The western massasauga (Sistrurus catenatus tergeminus) is a small, nocturnal, prairie-dwelling rattlesnake most numerous in north central Texas and seldom seen except on paved roads after dark. Its closely spaced brown dorsolateral blotches and comparatively slim head capped with nine large scale plates sets it off from rattlers of the genus Crotalus, as does its somewhat less potent venom. The desert massasauga (S. c. edwardsii) is a Northwest and South Texas massasauga. Sistrurus rattlesnakes such as the massasaugas and pygmy are thought to be less highly evolved than Crotalus rattlers due to their small rattle and the large cephalic plates they share with their moccasin-like ancestor.
The pygmy rattlesnake (S. miliarius streckeri) is a gray, black-blotched little viper with an orangish-tan vertebral stripe and a rattle so tiny that the snake is known locally as the rattle-less ground rattler. It is unevenly dispersed through East Texas. Its temperament is both secretive and surprisingly pugnacious, though the snake does not assume the elevated defensive-coil posture of larger rattlesnakes and has comparatively little venom.