Exploding plug prevents mating: honeybee
The mating apparatus of male honeybees prevents other males from mating with the queen after them by acting as an exploding, detachable plug.
"The mating apparatus of the male honeybee actually explodes and detaches, plugging the newly mated queen and preventing other males from mating with her." (Forsyth 1992:32)
Learn more about this functional adaptation.