Male Mongolian desert beetles perform oral sex on females to increase chances of sex, study finds

Warning: This story contains graphic descriptions of sexual activity. 

Male Mongolian desert beetles unable to satisfy females orally are less likely to convince them to have sex, a new study has found. 

But there's another good reason males are in no rush, the researchers revealed.

Darkling beetles of the species Platyope mongolica were rounded up during a recent mating season, and made to fornicate in the lab as scientists from the UK, US and China watched on. 

Much to the scientists' surprise, copulation began with an extended oral sex session - the male doing his best to prove his prowess to the female.

"Females displayed their abdominal terminus upward to show interest in sexual activity," the study, published in journal Ecology and Evolution, said. The male would use their mouth-based "maxillary palpi specifically to rub the female's genitals". If the female wasn't satisfied, she'd lower her rear and walk away. 

"In that case, the male continues pursuit and genital rubbing until another attempt to copulate. This procedure repeats until the male successfully inserts his aedeagus or the female rejects the copulation."

The longer the male went down on the female, the more likely she was to accept his advances - the latter often demanding five sessions before letting him get to the next base.

"On average, one copulation usually required at least as much time or more than that invested in oral sexual contacts," the scientists said. 

"Each step is important, and often, the individuals cannot move to the next step until the previous step has been correctly performed. If a male does not have a good performance in a certain step and moves too quickly to the next step, it most likely will need to return to a previous step again."

And if the male insisted on rushing, danger loomed.

"Sharp genital plates and narrow vulva in this species prevent the probability of smooth insertion absent of proper oral sexual stimulation."

The researchers said the longer a male satisfied a female, the less chance others would have to lure her away, and it also made the eventual copulation quicker - an advantage when there's no comfy beds, just "dry desert" and "bare sandy ground" to do it on. 

After the deed was done, the scientists found the males lost interest in the females altogether. Females also lost interest in males, but had to spend significant time fleeing other males who'd yet to find a mate, who'd get into fights with others pursuing the same female. 

"We also observed male–male touches during field observations," the scientists said, which didn't appear to be accidental. 

If you're wondering why scientists are studying beetle oral sex, the study says it's because they're trying to work out how its "evolutionary importance in sexual selection" - and they were inspired by other species which engage in "postcopulatory self-sucking", which is exactly what it sounds like.