Wildlife of Mount Diablo State Park - Tarantulas Usher in the Fall Season

Late summer and fall is tarantula time on Mt. Diablo. During this turn of the season, park visitors often see these hairy arachnids scurrying across trails and roads.

The tarantula, North America's largest spider, spends most of its life in and around its underground burrow. However, when a male tarantula reaches maturity at about seven years of age, he leaves the safety of his subterranean home to risk life and limb (all eight of them) in search of females of the species. These love struck males are the autumnal wanderers we see on the mountain.

Drawing by Nathan Crawford

Once a female tarantula is located by scent and enticed out of her den, the male tarantula faces the classic problem common to male spiders. He must convince the female he is a suitor and not just lunch on the hoof . Toward this end, male tarantulas have small spurs or hooks on their front legs to hold the female's savage jaws at bay during mating.

After mating, the larger, longer lived female returns to her borrow, ultimately to hatch hundreds of baby spiders the following spring.

A male that survives mating still faces a bleak future. The male spider never returns to his borrow and is doomed to die with the onset of cold weather.
Despite its fearsome appearance and formidable reputation, the tarantula is really a rather innocuous creature. The bite of a tarantula is no more severe than a bee sting. The spider's preferred defense mechanism is to flick the top of its abdomen with its rear legs. This action directs a spray of barbed hairs into the nasal passages and mucous membranes of any small mammal bent on making the tarantula its next meal. This behavior is why a tarantula will frequently sport a bald spot on its abdomen.

This hair flicking defense is ineffective against the tarantula's most feared enemy, the tarantula hawk wasp. This wasp seeks out and attacks the tarantula. After delivering a paralyzing sting, the wasp drags the tarantula to a hole and lays its eggs on the helpless spider. When the eggs hatch, the young wasps eat the tarantula alive.

As our wandering tarantulas run the gauntlet of tires, boots, voracious females, and assorted predators, all in the name of perpetuating the species, one can only marvel at this annual spectacle of nature.

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The above article by Ken Lavin was excerpted from MDIA's newsletter "Mountain News".

MOUNT DIABLO INTERPRETIVE ASSOCIATION
P.O. Box 346 - Walnut Creek, CA 94597-0346
(925) 927-7222 / FAX: (877) 349-5016