West Coast Widow Wars
I always had a deep respect for widow spiders because of their dangerous venom and fearsome reputation among people. When I was a young boy, I remember capturing numerous black widow spiders (Latrodectus hesperus) while rummaging through piles of scrap wood and old sheet metal in my back yard in the suburbs of Los Angeles. There were always plenty of black widows to be found back then.
I now study widow spiders as a graduate student at California State University Long Beach and my attraction to these spiders hasn’t changed and neither has my intent to learn more about them. However, I have noticed a change in the local spiders since my childhood. Nowadays, it’s much harder to find black widows in my back yard, and I sometimes even have to travel 40 to 50 miles to collect enough for my research. It also seems as if people are still scratching their heads as to what is happening to the city black widow population.
Where have the black widows gone? Why are they gone? Are any of them left? These questions have nervously caught my interest.
What’s even more nervously interesting is that there is a new species of widow lurking in the corners and crannies of California’s streets and homes – the brown widow (Latrodectus geometricus). A little over a decade ago, this spider was non-existent to So-Cal. Now, the brown widow has successfully spread from Los Angeles south to San Diego and as far north as Sacramento. Black widows are now extinct in my back yard, having been replaced completely by brown widows.
Each species have a reddish hourglass pigment on the bottom abdomen and both construct cobwebs that specialize in capturing small low-crawling prey. Brown widows are smaller, have spikey egg cases, more potent venom, yet bites to humans are virtually harmless. Black widows are larger, have pear-shaped egg cases, venom that is apparently not as potent, but bites to humans can cause painful bodily discomfort and even death to young children and the elderly.
These two species might be at war with each other in the cities and suburbs of Southern California. So far, my research has recognized that the introduced brown widow has intruded most of the urban cities lining the coast, exceptionally outnumbering black widows. Black widows maintain their dominance in more natural and low-developed landscapes. Both species will build cobwebs on the same urban structures (such as small buildings, bleachers, park benches and playground equipment) and both also seem to be eating the same types of prey. Both species can also be found living on the same structures at the same time.
Finding both widow species on the same playground set doesn’t mean they are getting along, however. Both species are known to be neighbors that eat the same prey, so competition for food and the best dwelling spaces may exist. Because there is evidence that brown widows are more urbanely plenty, and that the species is spreading throughout human populated areas, brown widows may be displacing black widows from their coastal city habitats. Whether this is true, however, is still in question.
What will the future be like for widow spiders in Southern California? Since brown widows are not known to be deadly to humans, should people really worry about disappearing native, yet more dangerous, black widows? Or will this new intruder be a coincidental blessing for human city residents by having the reputation as a safer, more tolerable, pest?
What ever the outcome may be, the brown widow species seem to have already made southern California a permanent home. For So-Cal coastal city black widows, home will never be the same again.
Marty is a PhD student at California State University Long Beach.