

Video: Young fruit fly cannibals feast on an older maggot Video: Young fruit fly cannibals feast on an older maggot

It’s the attack of the cannibal maggots: when larval Drosophila fruit flies find themselves short of food they swarm on their companions, tearing them apart and devouring them until nothing is left but a few mouthparts. The behaviour, seen for the first time in these flies, may be uncommon in wild flies, but researchers are eager to study its genetic basis in the lab.

Roshan Vijendravarma, an evolutionary biologist at the University of Lausanne, Switzerland, and his colleagues were studying how fruit flies adapt to food shortage when they noticed that young larvae would sometimes attack older ones that have grown sluggish as they prepare to pupate. When Vijendravarma looked more closely, he confirmed that the young larvae killed and ate their fellows. “It’s an easy source of protein, I suppose,” he says.

Further experiments showed that young larvae were attracted to the odour of wounded larvae, like sharks to blood, and that cannibalistic larvae could grow and mature even without any other source of food. Moreover, flies that had evolved under conditions of severe food shortage for 118 generations swarmed more aggressively around their injured companions and ate nearly twice as many prey as the flies raised normally – evidence that the behaviour has a genetic basis.

Since fruit flies are a favourite lab animal for genetic studies, the researchers hope to be able to pinpoint the genes that favour cannibalism – a rare treat for such a complex behaviour.


Finding such dramatic behaviour in such a well-studied species – particularly in one thought to be a mild-mannered rotting-fruit specialist – has startled fly researchers. “I’ve worked on Drosophila larvae since 1976, watched them in all kinds of different scenarios, and read the literature back to the 1940s. No one thought that they did this,” says Marla Sokolowski, an evolutionary biologist at the University of Toronto, Canada, who was not involved in the study.

Vijendravarma has not yet observed cannibalism in wild flies, only in lab cultures where flies were densely crowded and food was limited. Such conditions do occur in nature, although they are relatively rare, he says. The behaviour may explain why larvae crawl away from food at the end of their larval stage, he says – they could be searching for a safer place to pupate.

Nature Communications, DOI: 10.1038/ncomms2744