Bed bug (Cimex lectularius) intromittant organ, coloured environmental scanning electron micrograph (ESEM). During mating, the male pierces the body wall of one of the female's abdominal segments with this organ and deposits his sperm in a sac. The sperm then migrate through the body cavity to the seminal conceptacles, where they are stored ready for later fertilisation. Among the insects, this so-called traumatic insemination is unique to bedbugs and related families. The bedbug is a nocturnal parasite that feeds on the blood of humans and other warm-blooded animals. An adult bed bug is around 4 millimetres in length.