Are you an arachnophobe? Do creepy black spider Halloween decorations freak you out far more than any witch, bat, ghost or thing that goes bump in the night? Perhaps some factual information about our arachnid neighbors here in California could ease that fear. As this guide to the most dangerous spiders in California explains, spider bites are incredibly rare. Only a handful of spider species pose even the slightest risk to humans, and spiders are actually beneficial to our existence.
OK, so the rational, pro-spider position is unlikely to relieve a deeply felt phobia. A fear of spiders is typically less about genuine health concerns and more a visceral response to creepy, crawly creatures with eight hairy legs, fangs and multiple eyes. Reading up on different species can unlock new fears, but also reveal that spiders are pretty fascinating. Next time you’re startled by an unexpected spider encounter, just remember that it only wants to feast on mosquitoes, flies and cockroaches – not you.
[This article is for information only. It does not include medical advice.]
Are There Dangerous Spiders in California?
Yes. Yes there are. But not many!
There are around 40,000 spider species in the world, and California is home to just over 60 of them. Almost every spider species has venom and fangs. However, very few possess fangs capable of piercing human skin, plus venom toxic enough and in high enough doses, to cause significant injury to humans. Spiders are not aggressive toward people, typically only biting in response to accidental touch. They evolved to hunt insects, not large mammals.
In all of North America, only three spider species are capable of causing medically significant symptoms with their bites. Just two of those live in California: the black widow, found all over the state, and the invasive Chilean recluse, which is limited to pockets of Southern California. (The third dangerous spider species, the brown recluse, doesn’t live in the state. More on that below.)
Other local spider species can and do bite, but with little risk of serious injury. Among the worst non-medically significant examples are wolf spider bites, comparable to a mild bee sting. Further, a large number of medically diagnosed and self-diagnosed spider bites are a case of mistaken identity. A 2011 study found that of 182 patients diagnosed with “spider bites,” just seven of them were genuine spider bites. Most were infections unrelated to arachnids.
Black Widow Spiders in California
Californians are generally familiar with black widow spiders and their potentially dangerous bite, even if you’ve never actually seen one up close. Black widows are common all over the state. According to Dr. Stephen Lew of UC Berkeley’s Essig Museum of Entomology, black widows are the only spider with medically significant venom that anyone is likely to encounter in California.
Black widows do share habitats with humans, making their messy-looking, non-symmetrical webs in dark corners. But black widows are nocturnal, non-aggressive and generally avoid people. They prefer dry areas and might be encountered under ledges, stones and around outbuildings. Be extra careful when accessing storage areas and reaching into any dark nooks and crannies.
IDing a black widow spider
Female black widow spiders – the only ones that bite – are around 16 mm in body length. They are a solid, shiny black with a signature red, yellow or orange hourglass shape on the underside of the abdomen. Females sometimes have a row of red spots above the hourglass.
Males are about half the size of females, with longer legs. Males and younger females feature tan and white stripes or a marbled pattern, with males retaining those stripes into adulthood and females becoming gradually more black.
Black widow spider bites
Black widows possess one of the most potent venoms in the animal kingdom. Only females bite, and only when disturbed. Since antivenom became available in the 1930s, deaths from black spider bites have become virtually non-existent.
The response to a black widow spider bite varies by individual, and is more serious in small children and the elderly. The bite might feel like a small pin prick, but within 20 minutes to 1 hour leads to acute pain at the site. Within 1 to 3 hours after the bite, pain might spread throughout the body, and it can be considerable. Other symptoms include muscle cramps, dizziness, nausea, vomiting, chest pain, respiratory difficulties and elevated blood pressure.
Seek emergency medical attention for any whole-body symptoms and anything more than minor pain. Call 911 for severe symptoms.
Brown widow and false widow spiders in California
Brown widow spiders, a relative of the black widow, and false widow spiders, two different European invasive species, are present in California and often mistaken for black widows. False widows are similar in shape and size to black widows, but have a faint purple sheen. Their bites can be painful.
Brown widows are smaller than black widows, and can be brown or tan to black, sometimes with gray marbling. They also have an hourglass under their abdomen, usually orange to yellow in color. Brown widow venom is potent and their bites can hurt, but the venom is expressed in such small doses that it’s not really a concern. Brown widows are not native to California but have been introduced here, mostly in Southern California.
Chilean Recluse Spiders in California
Native to South America, invasive Chilean recluse spiders became established in the Los Angeles area in the late 1960s. Their discovery in a Sierra Madre theater inspired many sensationalist headlines due to the Chilean recluse’s highly toxic venom. This is the most dangerous of the recluse spiders, and one of the largest. Most disturbing is the human immune reaction to the venom, cutting off blood supply around the bite. The result is an open wound that’s very slow to heal, with potential complications. Sensitivity to the toxin varies, with some people experiencing no reaction at all. Fortunately, Chilean recluse spider bites are extremely rare in California.
Chilean recluse spiders span around 40 mm and are brown with a violin-shaped black mark pointing toward their rear. They are distinct from similar-looking spiders in having six eyes, rather than eight. These spiders are attracted to damp, dark, undisturbed places such as sheds, garages, behind pipes and under rotting logs. Arachnophobes should definitely avoid the basement of the downtown Los Angeles Goodwill store featured in this 2007 New Yorker feature story (a really good read).
Brown Recluse? Not in California!
Your uncle might swear he was bitten by a brown recluse in California, but that is almost certainly incorrect. Rick Vetter of the UC Riverside Dept. of Entomology is on a myth-busting mission to communicate that brown recluses are not, in fact, present in California. This species’ bite is of medical concern, but the closest known populations of brown recluse spiders are more than 1,000 miles from the state. Further, Vetter says that 90% of recluse bites are not medically significant and heal without the need for treatment.
The brown recluse’s similar-looking cousin, the desert recluse spider, is present in the sparsely populated southeastern quadrant of the state. Like the brown recluse and Chilean recluse, the desert recluse has a dark violin shape on its midsection, a uniform brown color and six eyes rather than eight.
Are You Still Scared of Spiders?
We have some mixed messages here. Spider bites are highly unusual, and when they do happen, most don’t cause much pain or require medical intervention. But, black widow spiders are common all over California, and their bites can cause serious medical issues requiring urgent care. Los Angeles area locals should be aware of Chilean recluses, but again, bites are almost unheard of.
Experts advise Californians to be cautious when reaching into and removing items from storage spaces. Containers and other items that haven’t been touched or moved in a long time are likely spots for spiders. Wear gloves and long sleeves as a precaution. Shake out shoes and clothes that have been left untouched for a while. Teach children to leave spiders well alone, and tell an adult if they see one.
Finally, if it’s around Halloween, there’s a good chance most of the spiders you see are plastic, and 100% harmless to humans.
If you’re someone who is more fascinated than afraid of spiders, check out “Museum Monday: Natural History Museum of Los Angeles County.” The museum hosts a seasonal Spider Pavilion exhibit.
Additional sources:
https://essig.berkeley.edu/identifications/spiders/
https://spiders.ucr.edu/myth-brown-recluse-fact-fear-and-loathing
https://skinparasites.ucdavis.edu/spider-bites
