We’ve known for years that female black widow spiders and other arachnids eat males during mating.
Now, new research shows that males of a type of ground spider known as Micaria sociabilis also eat females, and scientists are trying to figure out what motivates this behavior.
More than just a first date from hell, sexual cannibalism happens when one member of a species kills and eats a member of the opposite sex immediately before, after, or during mating.
This behavior is most common in arachnids like the black widow, as well as other invertebrates like insects, gastropods, and copepods. Most commonly, the female eats the male—but occasionally, the reverse is true. Male sexual cannibalism has been observed in another species of spider, Allocosa brasiliensis, and in crustaceans, but previously researchers had no idea what factors drove this behavior. (Watch a video of a male spider attacking a female one.)
On the surface, this seems like a pretty weird way to pass along your genes to the next generation. To scientists, however, sexual cannibalism can make a lot of sense. When prey is scarce and males are abundant, males become extremely valuable as a food source to females, noted study co-author Lenka Sentenská, a biologist at Masaryk University in Brno, Czech Republic.
Females invest much more energy into egg production than males do in sperm production, which tends to make them pickier about who they mate with. (See “Male Spiders Give ‘Back Rubs’ to Seduce Their Mates.”)
As well, not all males seem to fight being cannibalized, said Sentenská, whose study appeared recently in the journal Behavioral Ecology and Sociobiology.
“Males of some species voluntarily sacrifice themselves to a female, because such behavior enables them to copulate longer and pass more sperm. Males who are trying to escape usually copulate for a shorter time. Sometimes, this behavior is also viewed as an extreme paternal investment of the male, who sacrifices his body to provide nutrients to his future offspring via the female,” she said. [continue]
These articles, photos and videos tell a fascinating natural history story. The writer even gives motivation for both female and male behaviors. The back-rubbing male knows something important. I hope she spares his life.