The 3 Poisonous Spiders Found in California! (ID Guide)
Luckily, there are ONLY three types of poisonous spiders in California!
And fortunately, they only bite when disturbed or provoked. It’s important to remember that spiders would rather run away from you than bite. If you come across one of the spiders listed below, please DO NOT DISTURB!
Did you know that spiders are considered venomous, NOT poisonous?
There’s a common misconception between poisonous and venomous, one is ingested, and the other is injected. So, for example, If you eat something that makes you sick, it is considered “poisonous.” But if an animal, like a spider, delivers its toxins when it bites, then it’s considered “venomous.”
*WARNING – If you are bitten and think the spider is venomous, please go to the hospital!
If you have an allergic reaction, do not use this article to try to identify the spider. If possible, it is beneficial to try to capture the spider that has bitten you so they can determine the correct treatment.
Also, since spiders are predators, please know that every single species you come across can bite. And you may have a slight allergic reaction to many of them which are not on this list. For today’s post, I tried to focus on venomous spiders known to be very dangerous to humans when they do bite.
Also, if you enjoy this article, make sure to check out these other California guides!
3 Venomous Spiders That Live in California:
#1. Black Widow
- Females are 1/4 to 3/8 inches long—shiny black with distinctive red hourglass-shaped mark. A row of red spots is sometimes visible above.
- Males are half the size of females but have longer legs.
- Bristles on their hind legs, which they use to cover their prey with silk once it has been trapped.
Black Widows are the most venomous spider in California!
In addition, they are probably the most popular and recognizable spider in the world. Almost everyone can recognize the red-shaped hourglass mark that appears on the females.
Black Widow Range Map
But here’s the good news:
Even though they have highly toxic venom, 15 times stronger than a rattlesnake, they are not aggressive insects. The Black Widow only bites defensively if the web is disturbed, and they RARELY bite humans.
But, if you are one of the few unlucky people who are bitten each year, you should know that the venom affects your nervous system. Some people are only slightly affected by it, but many have a severe response. If you are bitten, the bite requires medical attention, and the neurotoxic venom can be fatal to small children if untreated.
Black Widows prefer dimly lit locations, dark corners in a basement, closets, and cluttered areas.
The best places to look for them include overhanging ledges, under benches or stones, near entrances to abandoned rodent burrows, or around outbuildings. They don’t like moisture and prefer dry areas.
Black Widows have a bizarre mating ritual. It begins with the male coming to the female’s web and destroying it. This reduces the female’s pheromones and makes the web less attractive to other males.
The females do not seem to mind the destruction of their property, and it actually seems to make them more receptive to mating. Even so, sometimes, the female kills and eats the male after mating. This gruesome behavior is what gave these poisonous spiders their name.
#2. Brown Widow
- Latrodectus geometricus
- Females are .25 – .625 inches in length and are light brown. The abdomen has an orangish hourglass-shaped mark.
- Males are roughly half the size of females. Look for an orange spot on the abdomen that may be broken into two spots.
- The legs on both sexes are light brown with dark brown near the joints.
- Also known as the Grey Widow
These venomous spiders are not native to California.
Brown Widows are believed to have originated in either Africa or South America. But now, they are found across the world, typically near buildings in warmer areas.
Brown Widow Range Map
In areas with both species, researchers show that Brown Widows are outcompeting and potentially displacing Black Widows. And while Brown Widows have dangerous venom, it’s less toxic than a Black Widow.
In addition, they are timid and rarely bite. In the rare case that a bite does occur, the symptoms include high blood pressure, sweating, vomiting, respiratory muscle weakness, and possible seizures. Sometimes you can develop a very stiff abdomen that may mimic appendicitis. The worst pain is generally in the first 8-12 hours.
#3. Black-Footed Yellow Sac Spider
- Cheiracanthium inclusum
- Pale yellow-beige color with dark brown markings on its palps, jaws, and on the ends of its feet.
- There is often an orange-brown stripe running down the top center of its abdomen.
- Also known as the American Yellow Sac Spider. As you can see, it gets its name from its appearance.
Yellow Sac Spiders are venomous and capable of biting humans.
Their bite begins with a bit of pain followed by itching and swelling. Symptoms from the bite typically are gone within 7-10 days. On the bright side, Yellow Sac Spiders rarely bite!
Black-footed Yellow Sac Spider Range Map
The severity of a Yellow Sac bite is not nearly as bad as a Black Widow or Brown Recluse. A study of twenty confirmed Yellow Sac Spider bites found that none resulted in necrosis (decaying of tissue due to cells dying). Instead, it seems like their bites cause swelling.
These venomous spiders are most often found in California on the foliage of trees and shrubs. But it’s not out of the question to find one in your house or other manufactured structures. Honestly, it’s pretty uncommon to actually see a Yellow Sac Spider unless you’re actively searching for one. The reason is that they are nocturnal and only come out at night to feed and mate.
Lastly, in 2011, Black-footed Yellow Sac Spiders caused quite a big problem for Mazda. The automobile company had to recall 65,000 Mazda 6 vehicles after discovering that webs from this species were clogging fuel system ventilation tubes. It seems that the spiders are attracted to the smell of gasoline, but it’s unclear why ONLY this particular model was affected!
Do you need additional help identifying a venomous spider?
Try this field guide!
Which of these venomous spiders have you seen in California?
Leave a comment below!