Study Finds Black Widow Species Which Reverses Sexual Cannibalism Roles

Black widow spiders are named after the phenomenon in which the females of the species chase down and devour the males after mating. According to new research, however, this isn't always the case, and in some scenarios, the roles are actually reversed.

A research team studied the Micaria sociabilis at Masaryk University in the Czech Republic. They paired up different spiders, and made sure they were well fed to rule out any instances of hunger-driven cannibalism.

Typically in black widow species, the female spiders would eat males after mating in order to kill off less desirable partners. However, the researchers observed many instances of the reverse situation, wherein the male spiders were the more choosy of the bunch.

They found that males often ate the females after the spiders' first contact and before any actual mating happened. These cannibalistic males were most often from the summer generation, and tended to be larger and more aggressive than their counterparts from the spring generation. Additionally, the scientists found that older females were more often eaten, even when they exhibited ideal breeding characteristics such as virginity or a large body size.

This study shows that male black widows in at least one species partake in cannibalism when choosing their mates, much as we previously knew the female spiders do. In addition, it seems that the female's age is the predominant factor in these instances. At least in the Micaria sociabilis, the female spiders are much more likely to be eaten than their male counterparts.

"Our study provides an insight into an unusual mating system, which differs significantly from the general model," said researchers Lenka Sentenska and Stano Pekar. "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 research was published in the scientific journal Behavioral Ecology and Sociobiology.