The War of the Black Widow Spiders

Our valley has a near-perfect climate and, as such, attracts newcomers from all over the world. Besides the human newcomers, foreign plant and animal life also do well here, so-called “invasive species.” In past columns, I’ve described several local “wars” involving the displacement of native species by non-native parrots, ants, squirrels and various plants. The latest loser in these wars will be our “beloved” black widow spider.

To anyone growing up in the Crescenta Valley, black widow spiders were legendary. They seemingly lurked under every rock, piece of wood, unused toy or play equipment. Our garages seemed alive with them and in our over-active minds they hunted children. They were evil looking – and deadly. Just a touch would result in agonizing death.

Like most of our childhood lore, the reality is quite a bit milder. Widow spiders are worldwide in various colorations. Our local widow, the western black widow, has the distinctive shiny black body with the iconic red hourglass on its belly. The bite, which we as kids considered deadly, is hardly so. Almost no one has ever died from the bite of a western black widow, and the worst that can be expected is muscle pain or cramping for a few days. Many who are bitten get no symptoms at all as the spider does not always inject venom with its bite. Even the name black widow is a slight exaggeration. In the wild the female almost never eats the male after mating. That generalization came from observing captive black widow mating, when the male was trapped in a container and couldn’t escape. In the wild, the male is always careful to make sure the female has just eaten before approaching, and he beats a hasty retreat after the act. By the way, the term for this behavior is “sexual cannibalism,” which is a wonderfully underused metaphor for some human behavior.

The black widow has been prolific all these years. But that began to change in 2002. That year, the LA County Museum of Natural History was conducting an urban spider survey. On an outreach trip to a Torrance elementary school, a kid brought over a brown spider on a leaf. The entomologist recognized it as a widow, but she had not seen that type before. She took it back to the lab where it was ID’d as a brown widow spider. The entomologists knew this native of Africa had been popping up in other parts of the world, but this was the first time it had been observed here.

Returning to the school, they found brown widows everywhere – under the school ground benches, on the chain-link around the school and in the play equipment.

It caused a sensation in Torrance, but remained localized there for a couple of years. Soon though the brown widow population exploded, and spiders began showing up in high numbers all over LA and San Diego. As their numbers went up, the numbers of the native western black widow went down.

The brown widows have basically the same behavior as the classic black widows. They nest in the same spots and compete for the same food. The difference is that browns reproduce about twice as fast as the blacks. Plus the babies spread faster due to a behavior called “ballooning.” They throw out a bit of web like a kite that catches any light breeze and they are lifted to ride to a new location.

How to ID brown widows? They are shaped like blacks and have the distinctive hourglass on the abdomen. However, on browns the hourglass is orange and is not as pronounced against the brown body, and the legs are tan with darker stripes.

The bad news is that the browns are quickly displacing the blacks and the blacks will soon be rare. The good news is brown widows are much less venomous, and bites are only slightly worse than a regular household spider bite. As this population shift takes hold, cleaning out one’s garage or bringing in firewood will no longer have the thrill of danger it once had.

  mike lawler