The brown widow spider is multiplying rapidly and settling in all over San Diego County -- from the coast to the inland valleys.
The venomous species, originally from South Africa, is established in tropical environments throughout the world, including Florida. It was discovered a few years ago in downtown San Diego.
Michael Wall, curator of entomology at the San Diego Natural History Museum, said an egg sack was probably shipped here with someone's patio furniture.
Brown-widow sacs contain 30 to 50 eggs, and the tiny spiders hatch after just 10 days of incubation. Wall said the species will continue to multiply and invade.
“Generally when you get introductions to any kind of invasive species, there’s kind of a beginning establishment period and then you get into what’s called an exponential growth phase where every year there’s more than the year before, and eventually it will settle out," Wall explained.
Unlike the black widow, the brown is shy and less aggressive. They generally retreat when disturbed, said Wall.
"They’re definitely dangerously venomous," said Wall. "They’re considered to be two times as venomous as our native black widow, but they inject about half the amount of venom as a black widow, so it kind of balances out so they’re about equal."
The brown widow’s bite is rarely fatal, but it could cause severe pain, nausea, high blood pressure, muscle cramps and a rapid heartbeat.
Wall said it’s not yet known if the brown widow will displace other native spiders. He said they feed on the same insects as the black widow and share the same predators.
