a parasite that prefers a crowd

By stunting the growth of potential queens, a fly can dictate the future of a tropical sweat bee colony. [sub. req.]

Megalopta genalis lives in colonies, where young female bees develop inside cells stuffed with nutritious nectar and pollen. A small parasitic fly called Fiebrigella can also lay its eggs inside these cells. When they hatch, the larvae steal the food stores, which stunts the developing bee's growth.

That has a profound effect on the bee's future. Large, well-fed bees stand a good chance of leaving the nest and starting a new colony as reproducing queens. Their stunted relatives, in contrast, have little chance of succeeding as colony founders. The best way to pass their genes on to the next generation is to become sterile workers labouring for the queen that bore them, which helps her to reproduce and pass down genes to the workers' sisters on their behalf. So the actions of the fly indirectly dictate who takes the crown.

"In Megalopta, the parasites promote sociality," says [UW's Sean] O'Donnell. His study is the first to show that a parasite can actually encourage group living in its host, he says.

Usually, parasites prefer introverts.