Western Diamondback

The western diamondback is an ambush predator that strikes accurately. Between each nostril and eye sits a heat-sensing pit about 5 mm (0.2 in) deep, which detects very slight temperature differences, so warm-blooded prey stands out even in total darkness. The snake also locates prey by smell. When it strikes, its long, tube-shaped fangs inject venom within seconds, and the prey is swallowed whole. Fangs are replaced 2 to 4 times a year, so a working set is always ready. Wild snakes eat only about once every 2 to 3 weeks. They also need little drinking water, because their yearly water intake roughly equals their body weight, and in dry areas most of that moisture comes from the prey itself. Patience and precision replace speed and effort. It is a calm, efficient way to live.

The famous rattle is built from hollow keratin segments, each one a remnant of a molted skin, and a new segment forms with every molt. Even so, counting segments cannot reveal a snake’s age. When threatened, a diamondback coils, raises the front of its body and shakes the rattle at 40 to 60 cycles per second, a sound that warns intruders to back away before any bite is needed. The species is generally shy and avoids confrontation with humans, yet it can be quick to bite when cornered. Black and white bands of nearly equal width circle the tail just before the rattle, so the warning is visual as well as audible. Its fangs and venom are a last resort, and the rattle is the first line of defence. Warning first, bite second.

Spring brings contests between males. Two rivals raise the front of their bodies up to 80 cm (31 in) off the ground and intertwine, pushing against each other until one gives up and backs off. This ritualized combat settles rivalry without a chase. Mating takes place in spring after the snakes emerge from hibernation, and in some places again in late summer and early fall. Both sexes become sexually mature at about 3 years old. Females often breed only every other year, but they may breed yearly when food is plentiful. Males mature at a snout-to-vent length of about 51 cm (20 in) and females at about 54 cm (21 in). A male that backs off lives to compete in another season, which makes the dance a clever alternative to a deadly fight.

The western diamondback gives birth to live young, though they develop from eggs held inside the mother, which is called ovoviviparity. After a gestation of about 167 days, a female gives birth to 10 to 20 young, averaging 14. Birth takes 3 to 5 hours, and litters usually arrive between June and early October. Newborns measure about 20 to 37 cm (8 to 14 in) and are described as precocial, meaning they are independent within hours. The young stay with their mother for a few hours, at most about a day, and then they are on their own. There is no nest, no feeding and no long period of parental care. A newborn must hide, hunt and avoid hawks, roadrunners and other predators almost straight away. Survival starts at the moment of birth.

When temperatures fall, western diamondbacks migrate to winter dens called hibernacula. In warm regions, they use rock crevices or convenient holes, while in colder places they take over the burrows of mammals such as prairie dogs. Several snakes may den together, so a single burrow can hold a whole neighbourhood. Their metabolic rate can drop by up to 70 percent, which lets them go several months without food. The snakes are more diurnal in spring and fall, and become more nocturnal or crepuscular in the heat of summer. Their range reaches from sea level up to about 2,440 m (8,000 ft), so the species copes with both hot desert flats and cooler highlands. Shared dens help many snakes survive the cold season. A good den can decide whether a snake survives until spring.

Hawks, bald eagles, roadrunners and wild turkeys prey on western diamondbacks, but people are the larger threat. Habitat loss, vehicle traffic and direct killing have caused local declines, and rattlesnake round-ups in Alabama, Georgia, Oklahoma and Texas remove many snakes. The biggest, in Sweetwater, Texas, has been held every March since 1958 and draws about 30,000 visitors. In the 1990s, up to 125,000 snakes may have been taken annually in Texas, though that figure covers round-ups in general, not this species alone. The effects of round-ups are unclear, and the snake is still listed as Least Concern because it is widespread. It also helps control rodent populations, which makes a healthy population of diamondbacks useful to the wider ecosystem. Fear is understandable, but their value as predators deserves attention too, across much of their range.