Role Reversal: Sexual Cannibalism Performed By Male Spiders

Some insects like black widow spiders and praying mantis have a nasty reputation for killing and eating their male suitors after mating, a phenomenon called sexual cannibalism usually only exhibited in females. But a new study that shows some male spiders have the tendency to kill and consume their female mates.

Researchers at Masaryk University in the Czech Republic have documented the male spiders in the Micaria sociabilis species are more likely to eat the females than be eaten.

 "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," the authors, Lenka Sentenska and Stano Pekar said in a statement.

Sexual cannibalism can occur for a number of reasons, including as a way to satisfy hunger, to combat an unwanted advance, as a way of rejecting unworthy mates, and has even been described as an extreme form of male monogamy in which the male will sacrifice himself to the female to gain reproductive success.

The researchers studying the Micaria sociabilis species suggest that this reverse sexual cannibalism may be a type of mate choice.

According to a press statement, the researchers collected male and female Micaria sociabilis spiders over a two-year period and studied their behavior by mixing males and females of the species at different time points. All spiders were well fed to discount cannibalism due to hunger. The authors observed what happened when they paired young adult male spiders with single female spiders either from the same generation (young female) or from another generation (old female). By pairing males with females of different size, age and mating status, the researchers hoped to be able to identify whether the reversed form of sexual cannibalism was an adaptive mechanism for male mate choice.

Cannibalism took place early after the first contact and before any mating took place. The researchers also observed that reverse cannibalism differed significantly based on the size of the spider; bigger males were more cannibalistic, suggesting male aggression may be related to male size.

The highest frequency of reverse sexual cannibalism occurred when larger, young males from the summer generation met old females from the previous spring generation, suggesting they may have based their choice on female age.

The research is published in the journal Behavioral Ecology and Sociobiology.