Until a recent study, scientists were unsure as to why male Mexican molly fish (Poecilia sphenops) sported an extravagant moustache-like structure on their upper lips. Close study of the fish’s sexual behaviour revealed that, much like in human gentlemanly circles, the females are drawn to the more luxuriantly moustachioed males. But, as recorded in Behavioral Ecology and Sociobiology journal, the molly’s tache has a more active sexual purpose, over and above the obvious aesthetic advantages of a sterling bit of face furniture: it is used to rub the female’s genitals and excite them into a frenzy of sexual activity.
The study was conducted by Professor Ingo Schlupp of the University of Oklahoma. He captured a selection of male and female Mexican mollies, and measured the length of the moustache on those males found to be growing one. The male and female fish were placed into tanks, and it was recorded how long females spent in the company of males sporting moustaches of various lengths, or none at all. The human equivalent would have been to place 100 chaps and chapettes in a cocktail bar and see whether the chaps with naked upper lips got any attention from the ladies.
The results were clear: on experiments involving over 100 fish, females consistently preferred males with moustaches. “The moustache-like structure seems to be a previously unrecognised sexually selected trait in poeciliid fishes,” the team of researchers wrote in the journal. Although they only tested the visual attractiveness of the moustache, the scientists strongly suspect that it also has a tactile function. With the absence of fingers with which to seductively twirl the tips of his moustache, the molly fish cuts straight to the chase and rubs his “lip weasel” against the female’s genitals.