A Fungus That Makes Male Flies Mate With Infected Corpses, Worse Than We Thought

A Fungus That Makes Male Flies Mate With Infected Corpses, Worse Than We Thought

A male fly tries to mate with an infected dead female

Not how I’d like my funeral if I’m being honest. Image credit: Filippo Castelucci/University of Copenhagen

Thanks to new research, a fungus that grows inside female flies, controls their behavior, and then explodes outside their abdomens has turned out to be worse than anyone thought.

Entomophthora muscae – translating quite satisfactorily to “fly killer” – is a fungus that infects house flies and fruit flies, among other species. Once a fly has picked up the fungus spores, it behaves normally for a few days, although those days are now numbered. The fungus grows inside, feeds on his insides and takes over his nervous system.

Four or five days after the spores have entered, the fly begins to behave strangely. He climbs to a climax in what is called “summit” behavior, sticking himself in place with liquid from his mouth. Once perched, it begins to contract.

The fly eventually spreads its wings upwards before dying and remaining in this strange position. This is when the fungus begins to emerge from the fly’s abdomen. For some reason, the strange fungus, more than worthy of its nickname, only kills at dusk.

By rising high, the spores can spread – but having the wings in an upright position also has its advantage. The male flies will mate with the corpse – attracted by chemical signals known as sesquiterpenes – becoming infested in the process.

“I think the big females are especially attractive to the males,” Brad Mullens, a retired UC Riverside entomologist, told KQED’s Deep Look, describing the whole ordeal as a fly nightmare. “If their little brain could figure it out, they would live in fear.”

So how do these creatures get worse, you ask? Well, new research from the University of Copenhagen has revealed that this chemically-induced necrophilia becomes more irresistible as the corpse rots.

The harrowing study compared the behavior of male flies around dead bodies of infected and uninfected females. The males were more likely to mate with the decaying females, which of course had been arranged by the fungus to appear receptive to mating. It only got worse as the females died.

“We see that the longer a female fly has been dead, the more attractive it becomes to males. This is because the number of fungal spores increases over time, which enhances the attractive scents,” the lead author explained. Henrik H. De Fine Licht in a press release.

In the study, 15% of males mated with corpses of infected females 3 to 8 hours after death. This figure increased to 73% 25 to 30 hours after death. Besides the obvious value of the study (learning about grotesque mushrooms), the research has practical applications.

“Flies are quite unsanitary and can make humans and animals sick by spreading coli bacteria and all the diseases they carry. So there is an incentive to limit house fly populations, in areas where food is produced for example,” Licht said.

“This is where the Entomophthora muscae mushroom can be helpful. We might be able to use these same fungal scents as a biological pest control that attracts healthy males to a fly trap instead of a corpse.”

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