Don't let the bedbugs, erm...

How male bedbugs avoid getting shafted

Bedbugs (rather like Tiger Woods) 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.