How does an ant queen communicate with her subjects in a colony of thousands? Scientists have discovered that, at least in one species, she does it by spreading chemical signals via her eggs.
Ant queens run an odd outfit. As with other social insects such as bees and wasps, worker ants benefit more by rearing their sisters--from the queen's eggs--than sons from their own unfertilized eggs. The queen is the linchpin of this system: In her presence, workers almost never lay eggs, and they quickly destroy any worker eggs that do appear. But little is known about how workers detect the queen in large colonies and distinguish between her eggs and those of other workers.
In the Florida carpenter ant, Camponotus floridanus, the queen lays eggs while the majority of the workers--numbering up to 10,000 per colony--remain infertile. C. floridanus workers don't have physical contact with their queen, so researchers suspected that the queen's signal is spread to the workers indirectly by means of her eggs or brood, explains entomologist Jürgen Liebig of the University of Würzburg in Germany. In a study published online in the Proceedings of the National Academy of Sciences this week, Annett Endler, Liebig, and colleagues investigated this possibility.
Their suspicions were confirmed when they found that workers still refrained from laying as long as the queen's eggs were present, even when the queen herself was removed. The key to the decision was the egg coating: Chemical analysis revealed differences in the hydrocarbons on the surface of queen and worker eggs. When the researchers coated worker eggs with queen-derived hydrocarbons, workers were fooled into accepting them as queen eggs. But workers destroyed queen eggs coated with worker-derived hydrocarbons.
The study is the first time ant queens have been shown to communicate using hydrocarbons on their eggs. Don't judge the queen an autocrat, though; Liebig says the hydrocarbons are less like a command than a polite suggestion not to reproduce. Because ceasing egg laying is in the workers' best interest as well as the queen's, no coercion is needed. Behavioral ecologist Francis Ratnieks of the University of Sheffield, U.K., agrees: “The queen only has to signal the workers, she doesn't have to dominate them.”