The reproductive organs of the male honey bee include testes, vas deferentia, seminal vesicles, mucus glands, an ejaculatory duct and an endophallus. The drone’s testes are fully developed during the late pupal stage, at which point they occupy much of the abdomen and are busy making spermatozoa. As the drone progresses toward early adulthood, the spermatozoa relocate from the testes, traveling through the vas deferentia to be housed in the seminal vesicles. As this is occurring the testes shrink and ultimately become rudimentary.
Two mucus glands sit astride the endophallus and empty into the ejaculatory duct where their contents mix with spermatozoa prior to ejaculation. The endophallus is a multi-component system comprised of a bulb, two chitinous plates, two membranous pouches called cornua or horns and the hairy patch. Larger than most other organs, the endophallus occupies a great deal of space in the drone’s abdomen where it resides in a deeply invaginated manner until copulation.
When a drone is successful in mating with a queen, his endophallus is essentially turned inside out. The pressure needed to evert the endophallus and drive the spermatozoa forth is created by his body diverting almost all its processes of circulation and respiration to this purpose.