Bark beetles use volatile fungal metabolites of plant defense substances as important chemical signals in their attack on spruce trees. A research team led by the Max Planck Institute for Chemical Ecology shows that the insects have olfactory sensory neurons specialized for detecting these volatile compounds. The fungal metabolites likely provide important clues to the beetles about the presence of beneficial fungi, the defense status of the trees, and the population density of their conspecifics. The study highlights the importance of chemical communication in maintaining symbiosis between bark beetles and their fungal partners.