Black spider seen frequently in Northern California house

Asked June 9, 2018, 11:18 AM EDT

We find these spiders in our home weekly. Mostly in May and June, but other times as well. What are they? They are often in our bedrooms on the walls and they move fast. We are worried about venomous bites, and would like to know where they are coming from and how to keep them out! I have lived in California for 40 years and have never seen this spider. Since we moved to a new house, we see this spider all the time inside only. It looks very much like the black house spider, but we read they are not native in CA. This spider is jet black. We do have black widows outside on our property, but these don’t have any markings and the body is not as bulbous. We have screens on all windows. They are either getting in from the attic or from under the house.

Marin County California spiders spider identification

1 Response

Dear Client,

I am hesitant to identify this spider. Some of the important features used to identify spiders are the body size, orientation of the six-eight eyes, appendages at the back end of the spider. orientation of the mouthparts relative to the body. A lot of this is a problem with the lack of contrast between features of the spider.

I would guess that this is one of the megalomorph spiders because of the body form; but it is not a tarantula (they have hairy legs!). It may be one of the trapdoor spiders that abound in California. It is likely to be coming from under the house or at the foundation of the house. All spiders have fangs and will bite in self-defense. Don't handle the big spiders. While your spider is not poisonous to humans (very few spiders in the USA are "poisonous" to humans), it will be painful if the fangs break the skin's surface. Always treat these "puncture" wounds with care and make sure the bite site does not become infected or inflamed. When this happens, always call and see your primary health care provider.

Hope this helps!