Male Black Widows Practice Cannibalism, Too

Lenka Sentenska via National Geographic
Lenka Sentenska via National Geographic / Lenka Sentenska via National Geographic

Black widow spiders, nature’s femmes fatales, have earned their name from a long-held belief that the females typically devour their male counterparts immediately after mating. But recent research has uncovered at least one species of the spider in which this less-than-romantic habit is reversed.

After studying different pairings of the spiders (making sure to keep them well-fed, in order to rule out hunger-driven cannibalism), a team at Mazaryk University in the Czech Republic has concluded that, within the Micaria socialbilis species, male spiders are actually much more likely to eat the females than to be eaten. Unlike the instances of female cannibalism, the M. socialbilis males most often eat the females after their first contact, before any mating has taken place. Older females are more likely to be eaten; in the study, the reverse sexual cannibalism saw a peak when summer generation males encountered older females from the spring generation. Among these older female spiders, even large body size or virginity—desirable traits that usually only whet a male spider’s sexual appetite—can’t save them from becoming a meal.

Despite the macabre subject matter and endless ammo for sexist jokes, the study is actually a breakthrough. Said researchers Lenka Sentenska and Stano Pekar in the journal Behavioral Ecology and Sociobiology, “Our study provides an insight into an unusual mating system, which differs significantly from the general model. Even males may choose their potential partners and apparently, in some cases, they can present their choice as extremely as females do by cannibalizing unpreferred mates."