Spider predator becomes prey
Wild Ideas
One of the things I like most about nature is that it continually surprises me, like the David-and-Goliath spider story that unfolded under my porch light recently.
Coming in my kitchen door one damp morning, I noticed a large, hairy Dolomedes tenebrosus,
commonly known as dark fishing spider, slowly making its way up the outside wall toward the porch light. I’ve had these spiders often visit inside and outside my house. In this column, I wrote about a particularly large one that crawled out from under my couch cushions a few years ago.
That one had a leg span of 3.25 inches and a body about 1.25 inches long, which is a bit beyond the normal range for this species. Judging by its size and shape, the current fishing spider was a young female, about half the size of the couch crawler. As in most spider species, the males are smaller than the females (half the size with this species) and more slender, and the current spider was quite plump.
The spider stopped for a while, so I went inside to get my camera. When I returned a few minutes later, I was amazed to find the spider looking ill and being wrapped in silk by a female common house spider (Parasteatoda
tepidariorum). In the cobweb spider family (Theridiidae), the house spider was about a third of the length of the fishing spider and not nearly as husky. Her legs were flying as she seemed to be trying to get more information about the larger spider with her front pair of legs while wrapping up the fishing spider in silk with her other six legs, called spinnerets.
Over the centuries of living in close proximity to us humans, the common house spider, which is primarily indigenous to the New World, has earned a host of other names, including American house spider, cobweb spider, domestic spider, comb-footed spider, tangle-web spider and gumfoot-web spider. This species boomed in and outside my house this year. Their normal prey are small insects, but I’ve seen them tackle prey as large as stink bugs. Still, huge predator she had tackled seemed out of her league.
Inside my house, the house spiders have always coexisted peacefully with another common indoor spider, the introduced
cellar spider (Pholcus
phalangioides). Although the cellar spider is thin, with long, spindly legs, if each species was rolled into a ball, they’d be about the same size. A female of each species has been sharing the space between my kitchen window and screen all summer with no apparent attempts to eat each other. The house spider even produced at least one egg sac during that time.
Almost all spiders have venom, but mostly only enough to subdue their small prey. In Virginia, only two types of spiders can be dangerous, if rarely fatal, to humans. First are the widow spiders, in a different genus of the cobweb family (Latrodectus).
The other is the brown recluse (Latrodectus reclusa) in the family Sicariidae, commonly known as violin spiders or fiddlebacks. Both widows and the recluse are shy and generally avoid humans and our dwellings, according to the Virginia Cooperative Extension (VCE) guide “Venomous spiders of Virginia” (ENTO73NP, downloadable from ext.vt.edu), only biting in defense when we brush up against them. Spiders tend to get a bad rap for mysterious, nasty wounds that suddenly appear on people, although even doctors find it difficult to nail down the cause unless a spider has actually been observed delivering the bite, the VCE guide adds.
While I missed the initial meeting of the two spiders under the porch light, the fishing spider did appear to have been injected with venom, as cobweb spiders do to immobilize their prey. The house spider backed off her prey for a few minutes, waiting for the bigger spider to become more manageable. The smaller spider then finished packaging her meal in silk and hoisted it up by a thread to her small, messy web (typical of cobweb spiders) under the light fixture. Perhaps she was just defending her home in attacking the fishing spider, with the huge meal coming as a bonus.
Being on the small side, cobweb spiders usually prepare their prey, after subduing them, by using their strong jaws to make small holes in the body, then vomit their digestive fluid into it, according to an article on the Burke Museum website (tinyurl. com/wi-cobweb-spiders). They then suck out and digest some or most of the muscles and internal organs, leaving a hollow shell. Over several days, I watched the little house spider under the porch light get fatter and fatter as she consumed her lavish meal.
Black widows, which are similar in shape and size to house spiders, are in the same spider family but a different genus. The house spider is browner and lacks some of the distinctive marks of the black widows, which in themselves vary is appearance by gender and age. Another cobweb spider, the introduced false black widow spider (Steatoda
grossa), is often also mistaken for a black widow but actually specializes in eating widow spiders, along with pill bugs. (Go online to the BugGuide website, bugguide.net, to see photos and descriptions of all spider species mentioned here.)
While the widows and recluse may prefer moreprivate places for their homes, the common house spider, like the cellar spider, has evolved to be a good housemate for humans, preying on real pests, such as roaches, mosquitoes, flies and clothes moths.