And even the best-defended females sporting the male versions sometimes end up injured and impregnated too.
The bugs exhibit a fantastic example of evolution at work, Reinhardt said, which is why he studies them.
Erik Svensson, an animal ecologist at Lund University in Sweden, called the bat bug findings important.
While male sexual differences within species have been well documented, he said, the females' physical responses have not.
Reinhardt added that it was "truly surprising" that males seemed to have copied females in the first place.
But, he added, "I suppose I never think of these things as shocking."
Spines and Twists
While African bat bugs might be one of the wildest examples, there are similar cases of apparent transexualism and even sexual sadism among other critters.
(Related: "Sex Tips for Animals—A Lighthearted Look at Mating" [September 12, 2002].)
The genitals of male seed beetles, for example, are spiny to help anchor the males inside the females as they work to impregnate them.
But the spines tend to damage females, so the females have developed tougher genitals. The males in turn keep getting spinier.
Seed-beetle researcher Göran Arnqvist, at Uppsala University in Sweden, said that the evolutionary advantage is competition between males. Tougher, spinier males are the ones most likely to pass on their genes.
As long as the spines don't get so extreme that they are sabotaging reproduction, the species won't lose out from the unusual technique, he said.
And in a literally twisted approach to sex, some species of duck seem to be going to great lengths to achieve reproductive control.
Patricia Brennan of Yale University and the University of Sheffield was part of a team that announced in May the discovery that some female ducks sport convoluted genitalia—dead-end sacs and clockwise coils—to prevent impregnation.
Male fowl, in turn, have been evolving to have longer phalluses.
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