Male brown widow spiders prefer mature ladies (even if it means getting eaten)

April 24, 2018, 11:59 a.m.
A brown widow spider in its web
Photo: Roy Niswanger/Flickr

When it comes to mating, young female brown widow spiders (Latrodectus geometricus) are clearly the best choice for males. They don't require long courtship periods, they're more fertile than their older counterparts and they're less likely to eat the male.

And yet males of this species seem to have a predilection for older lady spiders, according to a study published in the journal Animal Behavior. Older spiders require a lot more work to woo, and they're far more likely to eat the males after mating. The male spiders will even choose older spiders over fertile female spiders that are about to become adults, despite the obvious benefits.

"We thought that we would find some benefit that the males have in mating with older females," study co-author Shevy Waner, a graduate student at the Hebrew University of Jerusalem, tells National Geographic. "But so far we really don't understand why that's their choice."

Waner and his colleagues took nine adolescent, young adult and older female spiders, and placed them evenly throughout a greenhouse. They then let loose 11 virgin male spiders in the greenhouse, at an equal distance from each group of females. The researchers checked on the spiders every 45 minutes to see where the male spiders were congregating.

Almost all of them were fighting over the older females.

The researchers also placed a single male spider one-on-one with the same types of females. The males mated with the older female 100 percent of the time.

Fifty-seven percent of male spiders in the study that mated with an older female were devoured.

What's so alluring about these older females then, especially when the odds are high for death? The researchers think it could have something to do with changes in the spiders' pheromones. It's possible the females are changing their pheromones in an effort to increase their odds of mating if they haven't done so yet. The researchers hope to test this hypothesis by analyzing the spiders' pheromone levels in another study.

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