Tarantulas have long been portrayed as harbingers of horror. Many spiders are fierce, keen-eyed, sleek-bodied hunters that run, jump and even perform aerial stunts. Some display elaborate courtship dances, while others weave beautifully intricate webs. And then there are tarantulas. They’re like the stout, bespectacled, slow-moving kid in an athletic family. They’re too heavy-bodied to leap, their silk-weaving efforts are primitive and a love dance is wasted on them since they’re too shortsighted to recognize their mates. As for running, they can sprint short distances -- but then run out of breath and essentially pass out.
Horrifying creatures? Hardly. Today’s tarantulas, part of the Mygalomorphae group, are evolutionary leftovers, descended from ancestors who thrived in the Paleocene swamps before dinosaurs. A later group, the Araneomorphae, evolved into leaner, more athletic spiders with sharper eyesight and more efficient respiratory and circulatory systems, while the mygalomorphs remained mostly heavy-bodied and myopic.
Thirty species are found in the Southwest, but the one most often seen is Aphonopelma chalcodes, commonly known as the desert tarantula, or Arizona blond tarantula. The tawny females have a leg span of about 5 inches. Males are slightly smaller, darker and more slender, and are often seen trudging determinedly across the desert on summer evenings. Tarantulas are, indisputably, hairy. Not only do they have long, pale guard hairs that help detect vibrations, but their abdomens are densely covered with very fine barbed hairs. When threatened, a tarantula quickly kicks a cloud of these urticating, or irritating, hairs in its opponent’s face. While the would-be attacker wipes its eyes, the tarantula escapes.
Although tarantulas are venomous, to humans their bite is about as harmful as a bee sting. What hurts more is the physical damage inflicted from the two curved half-inch fangs that tarantulas use to pierce insects, reptiles or small mammals. Once the prey is subdued, the spider injects digestive juices. As the inside of the prey becomes soupy, the spider sucks out the fluid, leaving only a husk.
In nature, turnabout is often fair play, and tarantulas are a featured item on the menu for coatimundis, bears, javelinas and birds. Even some members of the fly family parasitize these large spiders. Most determined are female tarantula hawks, or pepsis wasps, which search out female tarantulas. After what can be a long battle, a successful wasp overpowers the spider with a paralyzing sting, lays her eggs on the helpless tarantula, then buries her alive as food for the emerging carnivorus larvae.
Not surprisingly, tarantulas are homebodies. If you’re fortunate enough to have a female in your yard, she’ll probably still be there long after your other neighbors have moved away. All tarantulas mature at about 10 years old, and females can live an additional 20 years. Tarantulas grow by molting, or shedding, their exoskeletons. It’s a strenuous, vulnerable time for them while trapped halfway out of their old skins. After molting, their bodies are soft and defenseless for several hours. Once males mature, they only have one mission: to find females. Being arachnids, all tarantulas have four pairs of legs. They also have another pair of leglike appendages, called pedipalps, which in males swell into a sort of sperm-delivery organ.
At maturity, the males weave a small web, deposit sperm on it and then “load” their pedipalps. When summer rains begin, they begin their mate search, ignoring food or water. When a male finds a female, she reacts by rearing up defensively and open-jawed. The male’s front legs have an extra claw that’s neatly designed to hook the female’s fangs in place. Once assured that his favorite female can’t bite him, he impregnates her. Female tarantulas are kinder to their mates than other spiders and rarely eat the males, who are all dead of exhaustion, dehydration and starvation several months later.
After mating, the female retreats to her burrow and weaves the bottom half of a silken egg sac. She lays her eggs on it, then weaves the top sheet and fastens the two layers together, much like a baby bassinet. She watches over the sac, even carrying it to her burrow’s entrance to warm in the sun. When the spiderlings emerge, all 800 of them, they remain with the mother through their first molt, then leave to establish their own burrows in the same neighborhood. Emerging spiders are a culinary treat for predators; of each brood, rarely do more than a couple youngsters survive to adulthood.
Occasionally, tarantulas wander into human habitation. Despite appearances, a tarantula is surprisingly fragile, and it can bleed to death if dropped. Use a dustpan and soft brush to gently sweep it into a large paper bag, and then release it in its native habitat. Chances are, a tarantula’s visit will prove far more horrifying for it than for you.