科学美国人60秒:Male Black Widows Strive for Mate's Monogamy

Island View Beach, in British Columbia, has all the makings of a perfect summer outing: great views, seclusion, sand dunes and driftwood. There's just one minor detail: That driftwood? It hosts two to three black widow spider webs per square meter. 

"To some people a beach full of black widows sounds like a nightmare, but to me it's awesome and it's not scary at all." Catherine Scott studies spider behavior at Simon Fraser University in British Columbia. And in case you're wondering: "I've never been bitten by a black widow and I'm not at all concerned about being bitten by a black widow." 

Scott's research brought her to Island View Beach, to study the mating habits of black widow spiders. The basics are this: "If you're a male black widow your goal in life is to find a female and mate with her and father as many of her offspring as possible." 

Achieving that goal includes some architectural alterations by the males during their several hours of courtship—they snip the female's web to pieces, and then bundle the tattered web in their own silk. Scott and her colleagues found that webs treated this way don't attract other prowling males the same way an intact web does. Meaning "it's not so much the best male, but the first male to arrive that will win, if he's able to quickly find a female and reduce her web." 

And the reason this tactic works? The researchers say females encode pheromones, like chemical "personal ads," in their webs, advertising their age, hunger level and mating status. And the first-arriving male's craftsmanship may obscure that information, causing other suitors to pass her by. The study is in the journal Animal Behaviour. [Catherine Scott et al, Web reduction by courting male black widows renders pheromone-emitting females' webs less attractive to rival males]

Wondering about the postcoital fate of the males? Scott says it's a common misconception that black widows always feast on their mates. Males can—and do—mate with multiple females. And besides, black widow females advertise right on their webs how hungry they are. So let no male claim that his desire caused him to lose his head.  

—Christopher Intagliata