Researchers have pinpointed a chemical source that attracts fruit flies to food: the gut bacteria of fruit-fly larvae sitting on the food.

Reuven Dukas and his colleagues at McMaster University in Hamilton, Canada, previously showed that fruit flies (Drosophila melanogaster) are attracted to food occupied by larvae. Now they find that the flies prefer food that has been inhabited by larvae with intact gut microbiomes rather than by bacteria-free larvae.

The authors also show that this attraction is not related to the presence of gut bacteria or larvae in the food, but to the physical changes that the feeding larvae make. Used food is easier for a larva to burrow into than fresh food, they say.

J. Exp. Biol. 217, 1346–1352 (2014)