An apple falls in an orchard and attracts fruit flies. Soon, the fruit is riddled with larvae, tunnelling inside it and digesting it from within. It’s a maggot party and, according to a new study, the invitation is written by microbes.

Fruit flies are naturally attracted to the smells of ripe and rotting fruit, but their presence on a piece of fruit draws yet more of their peers over. Zachary Durisko and Reuven Dukas from McMaster University discovered this in 2013: they showed that larvae are attracted to the odours of fruit that are already occupied by other larvae. These smells weren’t coming from the fruit itself or from the yeasts that were fermenting it. What was the source?

The team