The persistent embrace of onychophorans: What determines copulation duration in velvet worms?
In the only onychophorans mating that has been photographed, instead of fleeing, the couple remained together despite being manipulated. Why? The duration of copulation in onychophorans is possibly controlled by the female, larger and stronger than the male, probably with the participation of dopamine and γ-aminobutyric acid. Insemination through the body wall can be a male mechanism to overcome female defenses.