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Spiders are beneficial for their role as predators to insects and other arthropods. Unfortunately, many people fear or dislike them. Only one spider that lives in the Bay Area can seriously hurt humans, it is the black widow.

Spiders are not insects, they are arachnids. Spiders have eight legs and two body parts: a head region (cephalthorax) and an abdomen. They lack wings and antennae. Most spiders have toxic venom used to kill their prey.

One of the most common spiders found in a home is the longbodied cellar spider. It cannot bite humans because their fangs are too short to pierce human skin. Their biggest problem to humans is their messy webs.

Another common house spider is the common house spider. It makes its webs in corners and windows.

The red and black jumping spider is often found around homes. If provoked, it may bite, but bites are usually not serious. Jumping spiders do not make webs. They have very good eyesight to hunt with.

Black Widow

The black widow spider is the only spider in the Bay Area that is dangerous to humans.

The venom is 15 times as toxic as the venom of the prairie rattlesnake. However, black widow spiders are not usually deadly, especially to adults, because they inject only a small amount of venom. Only the female is venomous. Males are harmless.

The female black widow is shiny black, with a reddish hour glass shape on the underside of her spherical abdomen. Her body is about 1 1/2 inches long with a span up to 3 inches.

Adult males are about half the size of the females, with smaller bodies, longer legs and have an orangish hour glass shape on their abdomens.

Like most spiders, black widows prey upon insects and other arthropods. After she ensnares her prey in the web, she makes small punctures in the victim's body and sucks out the liquid contents.

Black widow webs lack shape and form. Their appearance is erratic, and the silk is stronger than any other spiders in this region. It is common to see leaves and other debris caught in the webbing.

Her webs can be found on the underside of ledges, rock piles, plants and debris, wherever a web can be strung. Usually low to the ground.

After mating, the female will make between four to eight egg sacs during a summer. Each containing up to 750 eggs.

The egg case is about 1/2 inches in diameter and suspended in the web. Its color ranges from white to tan and has a paper like texture.

After the eggs incubation period of 14 to 30 days the young black widows emerge and leave their mother's web.

The black widow spider is shy and nocturnal, usually hiding in her web, hanging belly upward.

Although not aggressive, she may rush out to defend her egg sacs. She will also bite when accidentally trapped in shoes or clothing.

Control of this spider can be done with an exterior treatment around the home.

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