Watch War-Painted Female Fruit Flies Fight After Sex

The French coined the term "la petite mort," meaning the little death, to describe the mellow, bittersweet buzz that many people report experiencing after sex. But female fruit flies, in contrast, feel no such post-coital chill, opting for more of a "fight to the death" vibe.

According to new research published on Monday in Nature Ecology & Evolution, there is a consistent uptick in aggressive bullying behavior between female Drosophila melanogaster fruit flies after they have mated with males, a shift that may be triggered by sex peptides in fruit fly semen. This conclusion was reached after several observations of recently bedded females duking it out with slap-fights, shoves, and even the dreaded fruit fly headbutt.

Yes, there's video evidence, and yes, it's adorable. Behold, a sperm-fueled gladiatorial showdown in a tiny "contest arena."

Aggression in mated female fruit flies. Video: University of Oxford/YouTube

The authors of the research, led by Eleanor Bath and Stuart Wigby of the Oxford University Department of Zoology, deemed fit to mark their female subjects with colored spots to keep track of them, but it may as well have been war paint given these "ejaculate-induced female aggression," in the words of the paper.

When compared to the interactions between virgin females, mated females fought over twice as often, though the exact underlying mechanisms behind these literal microaggressions remain unknown.

The team suggests two possible causes: Females may be indirectly prompted into shoving matches over resources by the new demands of egg production and impending motherhood, or they may receive a direct chemical signal from sperm that makes them less tolerant to their brethren. It will take more research to untangle the two possibilities, or to understand where they overlap, in order to solve the intriguing mystery of the post-coital testiness of lady fruit flies.

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