Scientists have proven for the first time that male flies enjoy orgasms, suggesting the association between pleasure and ejaculation evolved a long time ago. They've also discovered that male flies that aren't ejaculating to satisfactory levels will turn to alcohol instead.

You'd think it was something that scientists would have known for a while. It makes sense that ejaculating would be rewarding for males of pretty much every species, as this would encourage them to go out and do more of it, thus spreading their seed and continuing the species. 

However, it's not the easiest of things to prove. On a fly, you can't exactly see its climax face. Now researchers at Bar-Ilan University in Israel have come up with a novel way to find out.

In a study published in Current Biology, scientists genetically engineered male fruit flies that would respond to red light by ejaculating, all by themselves with no partner present. The light activated the neurons within the fruit flies' abdomens known to trigger an eruption of semen.

They then put these flies into a rectangular container, where half of the container was bathed in red light and the other half wasn't. They then monitored where the flies liked to spend their time. 

Unsurprisingly, the scientists found they preferred to hang out in the area of the container that caused them to spontaneously ejaculate on a regular basis. A pretty sure sign that they like to orgasm.

Next, the researchers trained the flies to associate the red light with a smell. They then removed the red light, instead making one end of the container scented and the other end scentless. The flies chose to spend most of their time in the area where the scent was, potentially as it reminded them of all those orgasms they so enjoyed.

As a final part of the experiment, the team looked at alcohol consumption by the flies. The flies were offered a choice of two food sources – normal liquid food and liquid food laced with ethanol.

The flies that were regularly ejaculating went for the normal food, whereas the non-genetically altered control flies, which were not receiving regular orgasms from the red light district of their containers, preferred to get drunk on the alcohol-laced food. They were getting off their faces out of sexual frustration.

“Sexual interactions with female flies that do not reach copulation are not sufficient to reduce ethanol consumption, suggesting that only successful mating encounters are rewarding,” the authors wrote in their paper. 

“Successful copulation is naturally rewarding to male flies... [and] sexually deprived male flies show increased motivation to consume ethanol."

The authors told Newsweek that the research applies to male fruit flies, and is not necessarily applicable to females, though the evolution of the clitoris suggests "female mammals can enjoy sex too".

Overall the research suggests that pleasure derived from ejaculating is a mechanism for survival that evolved long ago.

"The principles by which the brain processes reward are extremely conserved in all animals," said study author Galit Shohat-Ophir in a statement.

"This is a really basic everyday machinery that helps animals survive.”