Virgin Blood: Factors Influencing Sexual Cannibalism in Wolf Spiders

While some people may be familiar with animals who consume their partners during or after insemination like the black widow or praying mantis, fewer people are familiar with the practice of pre-copulatory sexual cannibalism that is common among the Lycosa fasciiventris, or non-burrowing wolf-spider. A number of theories were previously proposed as to why female wolf spiders would eat courting male spiders including the “adaptive foraging hypothesis” that a female wolf spider would choose to consume any males courting her if the nutritional benefit outweighed the risks of going without a mate. Another, non-adaptive hypothesis, the “mistaken identity hypothesis” simply stated that these pre-mating acts of cannibalism were caused by the female mistaking the male for some other prey creature.  A 2016 study looked at a number of factor including the amount of the food available to the female wolf spider, her age, and her relative size to her partner to see if there was any connection between them and the decision to cannibalize her partner pre-coitus. (Gavín-Centol, Kralj-Fišer, Mas, Ruiz-Lupión, & Moya-Laraño, J., 2016)

In this study, researchers took female wolf spiders that had never been exposed to male wolf spiders and raised them to sexual maturity before putting them on a high- or low-volume diet. Female wolf spiders on the high-volume diet were fed 1-3 crickets weekly and were continued to be fed until they were introduced to the male spiders. Female wolf spiders on the low-volume diet were only fed one cricket a week and were not fed two days before meeting the wolf spiders. The sexual size dimorphism, that is to say, the size difference ratio between the male and female in each pairing, was recorded. In addition to the variation in diets and size, researchers also chose to observe if the age of the female spider would have an effect on her choice to cannibalize her mate, introducing males to females from both food groups ten to fifty days after they reached sexual maturity. In the end, the results were clear: young, hungry females that were relatively larger than their partners were much more likely to consume them in the courting process.

These results show that this is indeed no case of “mistaken identity” for the wolf spider. Rather, it appears that the decision to eat her partner is one that the wolf spider makes based purely on pragmatism. So, if you happen to be a male wolf spider: beware! Or, at least, choose a young, well-fed, similarly-sized partner if you want to live.

Reference:

Gavín-Centol, M., Kralj-Fišer, S., Mas, E. D., Ruiz-Lupión, D., & Moya-Laraño, J. (2016). Feeding regime, adult age and sexual size dimorphism as determinants of pre-copulatory sexual cannibalism in virgin wolf spiders. Behavioral Ecology and Sociobiology, 71(1). doi:10.1007/s00265-016-2228-6