[3] The evolution of the spermalege as a female counter-adaptation for traumatic insemination was proposed by the French entomologist Jacques Carayon in 1966.
[3] In order to access the female's haemocoel during traumatic insemination, male bed bugs insert their needle-like aedeagus[5] into the groove, and pierce the pleural membrane.
[3] The ectospermalege is visible externally in most bed bug species, giving the male a target through which to impale the female.
In species without an externally visible ectospermalege, traumatic insemination takes place over a wide range of the body surface.
The ectospermalege appears to act as a mating guide, directing the male's copulatory interest, and therefore damage, to a restricted area of the female's abdomen.