Spider Sexual Cannibalism: Why Do Male Spiders Eat Old Females?

By Philip Ross on May 8, 2013 10:36 AM EDT

female black widow
The female black widow spider, whose venom is three times as potent as the males’, cannibalizes her spouse after mating with him. (Photo: Creative Commons)

Spider sexual cannibalism, in which one organism devours another before, after or during sex, is a macabre behavior - but that's part and parcel of life in the wild. And while the incidence of female spider cannibalism has been well documented, especially among the black widow species, little is known about male spider cannibalism - until now.

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Science Daily reports that researchers in the Czech Republic spent two years collecting male and female Micaria sociabilis spiders. They mixed different combinations of male and female spiders and studied changes in their behaviors.

Keeping the spiders well fed to account for hunger, the researchers found that the larger, young male spiders were most likely to cannibalize the older females, even before any mating occurred.

"Our study provides an insight into an unusual mating system, which differs significantly from the general model," the others commented. "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."

Bigger Micaria sociabilis males tended to be more cannibalistic than smaller ones, and the highest frequency of such incidents happened when larger, younger males were matched with older females. From Live Science:

Males ate the females typically after the spiders' first contact and before any mating, with the culprits most often males from the summer generation, the researchers found. These males tend to be larger than their counterparts born into the spring generation, suggesting size matters in aggression.

The findings are published in the journal Behavioral Ecology and Sociobiology.

According to a study published in the Annual Review of Ecology and Systematics, intraspecific predation is common in the animal kingdom, with about 1,300 species practicing cannibalism. Cannibalism occurs in some scorpions, fish, larvae and even primate species.

"In general, larger (older) animals are more voracious cannibals than smaller (younger) animals," the study reports.

Group cannibalism, in which a number of animals gang up and devour a weaker member of the group, has also been observed. Eggs and newborn animals, which are rich in nutrients and energy, are often consumed; cannibalism of offspring occurs in almost every major group of egg-laying animal, including gastropods, insects, fish, amphibians, birds and spiders.

Read more from iScience Times:

Bat-Eating Spiders In your Backyard? New Study Says They're Closer Than You Think [VIDEO]

Space Spider Dies in D.C. After 100 Days On International Space Station [VIDEO]

Black Widow In Grapes: Deadly Spider Discovered In Massachusetts and Rhode Island Supermarkets

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