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Tarantulas on Mount Diablo

Tarantulas on Mount Diablo

Mike Woodring

Why are tarantulas out wandering about? Late summer and fall is tarantula time on Mount Diablo. The tarantula (Aphonopelma sp.), North America’s largest spider, is nocturnal and spends most of its life in and around its underground burrow. However, when a male tarantula reaches maturity at about four to seven years of age, he sheds his exoskeleton for the last time, develops little spurs or hooks on his front legs, and leaves his subterranean home for good to risk life and limb (all eight of them) in search of females of his species with which to mate. These males are the autumnal wanderers we see on the mountain.

After a male locates a female by scent, he gently taps at the entrance to entice her out of her burrow to mate. He uses the small clasping hooks on his front legs to hold her fangs and bend her backward. Mating lasts from 30 seconds to a couple of minutes. After mating, the larger, longer lived female (she may live to the ripe old age of 20 years or more) returns to her burrow, ultimately to hatch a hundred or so baby spiders the following spring, of which perhaps one or two spiders will survive to adulthood. It’s not easy being a tarantula.

Will a female tarantula eat the male? It’s a myth that female tarantulas always kill the males after mating. On rare occasions, a female that has already mated several times and is approached by an amorous male may attack and eat the male rather than mate again. A female may consume the male if she is famished and needs a meal to be able to lay eggs, but almost always she allows the male to retreat to continue searching for other females until he succumbs to the elements in a few weeks, due to the onset of cold weather, starvation, or the jaws of a predator. Note to parents: A wandering tarantula won’t live long enough to make a good pet.

What do tarantulas eat? Typically, a hunting tarantula waits patiently in its burrow near the opening until an unsuspecting insect (usually a cricket) crawls by. The spider rushes out, bites the prey, and drags its victim back into the burrow. In the dark of night, this activity goes unnoticed (except by the cricket!).

Why do some tarantulas have a bald spot? The tarantula’s main weapon against larger creatures is defensive. If a bobcat or fox is harassing it, the spider rises up on its front legs and with its back legs scrapes off a cloud of barbed, porcupine-like hairs from its abdomen into the nasal passages and mucous membranes of its tormentor. This tactic sometimes gives the tarantula time to escape and is why a tarantula may sport a bald spot on its abdomen.

Who is its most feared predator? The large black and orange female tarantula hawk wasp (Pepsis sp.) seeks out and attacks the tarantula. After delivering a paralyzing sting under a leg, the wasp drags the tarantula to a hole and, before covering the tarantula, she lays a single egg on the helpless spider. When the egg hatches, the young wasp larva eats the tarantula alive.

How bad is a tarantula’s bite? Despite its fearsome appearance and formidable reputation, the tarantula is really a rather innocuous creature–a terror to small insects and not much else! Tarantulas have very small venom glands, and its very mild venom is only strong enough to paralyze a cricket, with practically no effect on people.

Mount Diablo’s tarantulas are really gentle souls that play an important part in the web of life on our island mountain. So the next time you encounter a tarantula on the trail, remember the old adage, “If you wish to live and thrive, let a spider run alive!”

Download Tarantulas: Protect These Gentle Giants Brochure (pdf)

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