Tarantulas: The Gentle Giants of Mount Diablo

by Naturalist Michael Marchiano

Each year in late summer, male tarantulas born between four and seven years ago find a secluded place and lay down a sheet of silk webbing. Resting on top of the silk, they split their outer skin covering the thorax and, over several hours, slowly extract their legs and slough off their old skin. This is their final molting. This new adult male tarantula is an exact replica of the prior one except he now possesses “nuptial” hooks on his fore legs to use in matting over the next couple of months.

 

From mid August to late October, the East Bay area male tarantulas (Aphonopelma iodius) will be on the prowl. Their counterparts, the females, will be staying at home in burrows where they have lived for as long as twenty-five years. The females also reach maturity after between four and seven years, and it is unknown whether they mate every year.

 

In fall, those that wish to mate will clean out the entrances to their burrows and cover them with a thin silk cover. The amorous males, who may wander as much as a mile while searching for a female's burrow, are probably attracted by some form of pheromone. When located, the males tap out a message on the silk explaining their mating intentions, assuring the female they are not a threat nor should she consider them a meal. As the female comes out of the burrow, the male will back up and allow her to approach, touching legs. The male then cautiously bends the female backwards using the hooks on his front legs to hold onto her fangs while mating. Mating may last from thirty seconds to three minutes and before the male releases the female, wandering off while she returns to her burrow.

 

For the next two months, the male will continue looking for other females to mate with, growing weaker and finally dying as winter approaches. The female will overwinter in her burrow, occasionally coming out at night to capture a meal. In late winter to early spring, the female will weave a silk pillowcase in which she will lay 100 to 150 tiny eggs. She will care for the eggs for approximately 30 days, at which time she tears a small slit in the egg case and the tiny white pinhead-sized spiderlings hatch out. Within a few days, the spiderlings will molt, shedding their exoskeleton for the first time. They disperse immediately since they are susceptible to many predators, including each other. Over the next four to seven years, the survivors living in their separate burrows will molt and grow, feeding at night and hiding during the day.

 

North American tarantulas have a very mild venom that can easily paralyze a small arthropod but it is totally harmless to humans. They do possess tiny barbed hairs on their abdomen that can be sluffed off into an attacker’s face, causing itching and watery eyes. Hollywood and the media have made tarantulas seem monstrous, so to many people these slow-moving spiders appear ominous and threatening. Nothing is farther from the truth; they are truly one of the gentle giants of the animal world.

Tarantula - Oak Knoll Trail | Kevin Hintsa

© 2019 by Mount Diablo Interpretive Association