Spider Bites in Los Angeles: Which Spiders Bite, What to Do

In Los Angeles County, two spiders cause medically significant bites: the western black widow and, with far milder effects, the brown widow. Brown recluse spiders have no established populations in California. Many sores blamed on spiders are skin infections such as MRSA, or bites from fleas, bed bugs or mites. A true black widow bite brings spreading pain and muscle cramping within about an hour, and it needs medical care.

Which spiders in Los Angeles actually bite people?

The widow spiders are the ones that matter medically here, and both usually nest outdoors. UC IPM calls the western black widow the spider posing the greatest envenomation threat to humans in the western United States. Even so, UC IPM says, black widow bites "are quite rare, even where these spiders are very common," and almost all medically important bites come from adult females.

Western black widow. The adult female is about 1/2 inch long, shiny jet black, with a red hourglass under the abdomen. She webs in garages near doors and vents, and outdoors in holes between bricks, gaps around pipes, rock crevices, woodpiles and clutter. Her egg sac is a tough, yellowish teardrop.
Brown widow. Established in Southern California in the first decade of the 2000s. About 3/8 inch, mottled tan, brown and gray, with an orange hourglass instead of a red one. UC Riverside lists nursery pots, plastic trash can handgrips, the undersides of outdoor furniture and mailboxes among its nest sites. Its spiky egg sac looks like a very large pollen grain.

What does a black widow bite feel like, and which symptoms need urgent care?

The bite itself is often painless or feels like a small pinprick, UC IPM says, with at most a little red mark. The venom is a neurotoxin, and other symptoms may appear within an hour. NIOSH describes pain at the bite that then "spreads to the chest, abdomen, or the entire body."

Symptoms that NIOSH and UC IPM list include:

Pain radiating from the bite, muscle pain and cramping, and rigid stomach muscles that UC IPM notes have been misdiagnosed as appendicitis
Sweating, nausea, vomiting, headache, restlessness, fever or chills, high blood pressure, and difficulty breathing

NIOSH states that death "can occur in the most severe cases," although it is extremely rare. An antivenom exists, and UC IPM advises anyone bitten to "seek medical attention immediately." Chest pain, trouble breathing or severe spreading pain means an emergency room.

Why are so many "spider bites" not spider bites?

Because infections and insect bites look like spider bites. The CDC says people "sometimes confuse some MRSA skin infections with a spider bite." It adds that "you cannot tell by looking at the skin if it's a MRSA infection." In a national study that UC IPM cites, 29% of patients seen for a "spider bite" actually had MRSA.

In 2002, 928 inmates at the Los Angeles County Jail were diagnosed with MRSA wound infections. The CDC's report on that outbreak notes that "patients were reported as having spider bites but subsequently were found to be infected with MRSA."

Clues that point away from a spider:

Several sores, or several people with sores at once. UC IPM says spiders "typically bite only once," and multiple lesions point to a contagious infection or to fleas, mites or bed bugs.
A red, swollen, painful bump, warm to the touch or full of pus, which is how the CDC describes MRSA.

The CDC advises covering the sore with clean, dry bandages, not picking or popping it, and seeing a provider for fever or no improvement within 48 hours.

UC IPM is blunt: "there are no populations of the brown recluse" in California. Fewer than 20 verified specimens have turned up over several decades. A related Chilean recluse lives in parts of Alhambra, Sierra Madre, Monterey Park and San Gabriel, usually in dark commercial and municipal storage basements rather than homes. If a clinic diagnoses a "recluse bite" without a spider, ask about MRSA.

What first aid should you do after a spider bite?

Wash it, cool it, and get it checked. NIOSH lists these steps:

Stay calm, and identify the spider only if you can do so safely.
Wash the bite area with soap and water.
Apply a cloth dampened with cold water or filled with ice, and elevate the bite area if possible.
Do not attempt to remove venom.
Seek professional medical attention right away.

NIOSH also recommends keeping tetanus boosters up to date, every 10 years.

How do you keep widows away from the places you put your hands?

Change the habits that put a hand in a web, then clear the webs. NIOSH notes that spiders "are usually not aggressive, and most bites occur because a spider is trapped or touched." Reaching blind into a woodpile or under a patio chair is the classic setup.

Inspect or shake out shoes, gloves, towels and clothing before use, as NIOSH advises. Keep gardening clothes and gloves in bags closed with zipper locks or twist ties.
Wear gloves, long sleeves and long pants when handling stacked wood, boxes or stored items.
Check the undersides of plastic patio furniture, trash can handgrips and nursery pots for spiky brown widow egg sacs.
Sweep, hose or vacuum webs and spiders off the building regularly. Store items in taped boxes off the floor and away from walls, and reduce clutter, woodpiles and heavy ground cover.

Skip the spray-and-forget approach. UC IPM states that "insecticides do not provide long-term control" of widows. In a 2016 study it cites, water-based insecticides sprayed on brown widow egg sacs had no significant effect on the eggs inside. For what draws spiders in, read why spiders are in your home and what they are really after.

When should you call a professional for black widows?

Call when you find widows or egg sacs where children and pets reach, or when webs return within weeks of cleaning. A PesPro spider control visit removes the spiders, clears the webs, creates a perimeter barrier, and addresses the insects that attract spiders to the property. Ongoing coverage runs through our general pest control program on a bi-monthly or quarterly schedule.

PesPro has served Los Angeles and San Bernardino counties since 2011, is QualityPro certified, and holds California Structural Pest Control Board License #PR-6378. The written quote is free, and same-day service costs an extra fee that depends on the route. Spiders fall under the second tier of our 30-day guarantee: another visit within 30 days costs 30% of the original price. See our service areas or request a quote.

Frequently asked questions

How soon do black widow bite symptoms start?

The bite itself may be painless or feel like a small pinprick, according to UC IPM. Within about an hour, other symptoms may start: spreading pain, muscle cramping, rigid stomach muscles and sweating. UC IPM and NIOSH both advise seeking medical attention right away. Chest pain, severe spreading pain or trouble breathing means an emergency room.

Is a brown widow bite dangerous?

Rarely. UC IPM reports that the brown widow's bite is "much milder than that of the western black widow." In an African study of 15 verified bites cited by UC Riverside, the two main effects were pain at the moment of the bite and a red mark. UC IPM notes one verified bite that required hospitalization, so spreading pain still deserves a doctor's call.

How can I tell a spider bite from a MRSA infection?

You cannot tell by looking at the skin, and the CDC says so directly. A widow bite produces body-wide symptoms, such as spreading pain, rigid stomach muscles and sweating, rather than a growing sore. The CDC describes MRSA as a red, swollen, painful bump, warm to the touch or full of pus, sometimes with fever. See a provider either way.

Do bed bug or flea bites get mistaken for spider bites?

Often. UC IPM lists mites, fleas, bed bugs, ticks and conenose bugs among the blood feeders whose bites get blamed on spiders. Our guides to bed bugs in Los Angeles County and fleas and ticks at home explain how to confirm each one.