I have a family of widow-type spiders living in my outdoor worm bin. I like spiders and all they do around the garden, and have a no kill policy toward them in general. This particular situation, however, has had me a teeny bit nervous. They hang out on the underside of the lid of the worm bin for the most part, though I’ve seen them on the surface of the worm compost once or twice. Obviously my concern is that I will touch one when opening or closing the bin, or while burying my kitchen waste.
Believing these spiders to be black widows, my options have been either to be very attentive while around the worm bin–or to roll out the vacuum. So far I’ve opted for being careful.
The thing about these spiders is that they lack the identifying spots on their abdomens, but I remembered being told somewhere that not all types show the red marks, and that males never do. Was this true? Were there other types of spiders that looked like this? After weeks of tip-toeing around the worm bin, I finally got around to doing some research. My conclusions are not conclusive, so I’m coming to you, dear readers, for help.
Wikipedia’s entry confuses me a bit:
Not all adult black widows exhibit the red hourglass on the ventrum underside or top of the abdomen — some may have a pair of red spots or have no marking at all. Female black widows often exhibit various red markings on the dorsal or top side of the abdomen, commonly two red spots. However, black widow young are believed to have at least some sort of marking on their abdomens. Adult male black widows are half the size of the females, and are usually gray or brown rather than black and red; while they may sometimes have an hourglass marking on their ventral abdomen, it is usually yellow or white, not red. Variation in specifics by species and by gender is great; any spider exhibiting a red hourglass or a pair of large red round spots on the ventral abdomen with an otherwise black shiny body is an adult female black widow.
Here is how I read this: Not all adults display an hourglass…but females often display some sort of red mark. Young and males may or may not have some kind of mark, but not red…but be careful! Variations by species and gender are significant. If you see a black spider with red markings, be very, very afraid. That there is definitely a female black widow. But really, there’s no guarantees here that other less flashy spiders aren’t some kind of dangerous, either.
This is not reassuring.
But then on the handy page Frequently Encountered Spiders in California, I learned about the False black widow.
Another European invasive, this spider seems to be displacing our native black widows in urban areas. This spider is roughly the same size and shape as a black widow, but is brown with a faint purple sheen.
I like this false black widow option a lot. The false widows don’t have a dangerous sting.
The spiders in my box are pretty shy, but insofar as I can tell, they are all sort of an eggplant color–not that true, bad-ass black of a classic widow. Nor have I seen any red marks. (That doesn’t mean that big mama with her red marks isn’t hiding somewhere.)
So, from this not-so-great photo, can anyone tell me if this particular spider might be a false widow, Steatoda grossa, or a male black widow, Latrodectus hesperus? It’s about 1/2 inch in size.
UPDATE 5/10: After reviewing the evidence, I believe this is a false black widow. However, my trouble are not over, because it turns out that they do have a venomous bite, apparently somewhat like a mild black widow bite. Here’s the bite intensity scoop according to UC IPM: black widows: obviously bad; brown widows: mild; false black widows: moderate.
