Flip over the patio chair you have been sitting in all summer and check the underside of the arm. In most Lake Elsinore backyards there is a decent chance you will find a tan spider with a mottled abdomen and a small spiky egg sac tucked beside it. Brown widows arrived in Southern California relatively recently and moved into suburban yards without much fanfare, which is why Main Sail Pest gets called to homes where a family has been walking past a dozen of them daily for a year. They are not hiding. People just are not looking under things.
What is a brown widow, and when did it show up here?
A brown widow is a close relative of the western black widow, in the same genus, with the same hourglass marking in a different color. The species became established in Southern California in the early 2000s and spread quickly through coastal and inland suburbs.
Color is a poor identifier on its own. Brown widows range from light tan to nearly black, usually with a mottled, geometric pattern along the top of the abdomen and faintly banded legs. The hourglass on the underside is orange to yellow-orange rather than the bright red of a black widow.
How do you tell a brown widow from a black widow?
The egg sac settles it faster than the spider does. A brown widow egg sac is tan and covered in small silk spikes, so it looks like a tiny sea urchin. A black widow egg sac is smooth, pale, and pear-shaped.
If you find a spiky egg sac, you have brown widows, regardless of how dark the spider looks. That single detail is worth more than any color comparison, and it is visible from a few feet away once you know what you are looking at.
Brown widows also produce egg sacs far more prolifically, with each sac holding on the order of a hundred or more eggs. That reproductive rate is why a single female becomes a wall full of them in one warm season.
Where are they actually living on your property?
Brown widows prefer exposed, off-the-ground crevices rather than the dark undisturbed corners black widows favor. The spots we find them most often:
- The underside of patio furniture arms, seat frames, and table rims
- Voids and gaps in block wall construction, especially along the top course and at pilasters
- The lip and drainage holes underneath potted plants
- Mailbox undersides and the inside of the door
- Playground equipment, particularly under slides, platforms, and handrails
- Gate latches, hose reels, barbecue grill shelves, and the rim of storage bins
- Water meter and irrigation valve boxes
Notice how many of those are places a hand goes without looking. That is the actual risk with this species, not aggression.
Is a brown widow bite dangerous?
Less dangerous than a black widow bite in practice, though the reason is a little counterintuitive. Research from UC Riverside has reported that brown widow venom is comparably potent drop for drop, but the spiders deliver much smaller amounts and are far more reluctant to bite, so envenomation usually stays localized.
A typical bite produces pain, redness, and swelling at the site rather than the muscle cramping and systemic symptoms associated with black widow envenomation. Anyone with spreading symptoms, severe pain, or a bite on a child or older adult should get medical attention rather than wait it out.
Is it good news that brown widows are pushing out black widows?
Partly. Studies in Southern California have found brown widows displacing black widows from some urban habitat, and trading a medically significant spider for a less significant one is a real improvement.
The tradeoff is density. Brown widows tolerate exposed, high-traffic locations that black widows avoid, and they reproduce faster, so a yard that had a handful of black widows in the back corner can end up with several dozen brown widows on the furniture, the wall, and the play structure. Fewer serious bites, many more encounters.
Why doesn’t a spray by itself solve it?
Because spiders make poor targets for residual products. They walk high on their legs, spend most of their time on web rather than on treated surfaces, and do not groom themselves the way ants and roaches do, so they pick up far less material.
Physical work carries the results. De-webbing the eaves, wall caps, furniture, and equipment removes the spiders and their egg sacs directly, and egg sacs need to be collected and disposed of rather than knocked to the ground, where they will still hatch. Main Sail Pest pairs that removal with targeted treatment of the voids and harborage points, then repeats on a schedule, since neighboring yards and open space keep supplying new spiders.
What can you do between visits?
Wear gloves when moving pots, furniture, and stored items. Keep clutter off the side yard, since stacked bins and unused furniture are the best habitat on most properties. Swapping bright white exterior bulbs for yellow ones cuts the insect traffic that feeds the population.
Check the undersides this week, before someone else finds one first. If you turn up spiky egg sacs on the wall or the play structure, Main Sail Pest can clear them out and keep the wall from filling back in.