Back-off warning has failed in this instance (Image: Dr Camilla Ryne)

BEDBUGS are notoriously undiscerning about who they mount, and are wont to stab their penis straight into another male’s abdomen. Now it seems they have evolved a way of telling mistaken mounters to back off.

Female bedbugs have a structure beneath their carapace to guide the penis into a mass of infection-fighting immune cells, but males have no such protection. Camilla Ryne at Lund University in Sweden found that they respond instead by emitting a pheromone normally used to warn off predators.

Males with blocked glands were mounted …