Male desert beetles perform oral sex on females to increase the chance of successful mating, a rare phenomenon in the animal world, according to a scientific study.
Scientists have for the first time observed precopulatory oral sexual behavior in the desert darkling beetle, P. mongolica. Before male beetles insert their aedeagus into the female body, they would use their maxillary palpi, a sensory organ on the mouth, to rub the female's genitals.
If she is not satisfied with the male’s performance and runs away, the male would continue pursuit and genital rubbing until another attempt to mount and copulate, according to the study published in Ecology and Evolution in August. It was authored by researchers with the Chinese Academy of Agricultural Sciences and the University of Missouri.
The lead author, Xinghu Qin, told Scientific American that he first spotted the beetles’ oral sex ritual near Inner Mongolia’s Hunshandake Desert.
Through a series of experiments, including ones in which researchers removed the mouth parts males used to perform oral sex, they concluded that oral sex helped the male beetles increase their chances of successful mating and might be favored in natural selection.
“Investment in oral sexual contact promotes the successful insertion by stimulating the opening of the vulva,” they wrote. “Oral sexual contact not only promotes mating success but also reduces the unsuccessful insertion cost and copulation duration.”
They also noted that male beetles who failed to engage in the courtship found little mating success, saying that “interference in oral sexual contacts decreased the proportion of successful copulation.”
Researchers added that mating on bare sandy ground in dry desert could expose the beetles to heat stress and prey risk, and oral sex promotes the efficiency of the mating process. On average, they said, one successful insertion usually required at least as much time or more than that invested in oral sex.
“The shorter a male spends on oral sexual contact, the longer a male spends on copulation attempts, and the more likely it is to be unsuccessful,” they said.
Few cases of oral sex has been observed in insects. Similar behaviors have been documented in Darwin’s bark spider and fruit flies, but precopulatory oral sexual behavior is rare for invertebrates.