Zombie fly fungus 'bewitches' healthy males to mate with infected corpses

Most of us don’t have much sympathy for common house flies - but male flies are targeted by a particularly loathsome zombie sex fungus, a new study has shown.

The fungus ‘bewitches’ male houseflies and causes them to commit necrophilia with the infected corpses of dead female houseflies.

The researchers say that the finding could lead to new and effective ways to trap flies.

After having infected a female fly with its spores, the fungus spreads until its host has slowly been consumed alive from within.

After roughly six days, the fungus takes over the behaviour of the female fly and forces it to high ground, whether upon vegetation or a wall, where the fly then dies.

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When the fungus has killed the zombie female, it begins to release chemical signals known as sesquiterpenes.

Henrik H De Fine Licht, associate professor at the University of Copenhagen's Department of Environment and Plant Sciences, said: "The chemical signals act as pheromones that bewitch male flies and cause an incredible urge for them to mate with lifeless female carcasses.”

"Our observations suggest that this is a very deliberate strategy for the fungus. It is a true master of manipulation – and this is incredibly fascinating.”

As male flies copulate with dead females, the fungal spores are showered onto the males, who then suffer the same gruesome fate as the females.

In this way, Entomophthora muscae spreads its spores to new victims and ensures its survival.

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The researchers found that dead female flies become more attractive as time passes.

Specifically, 73% of the male flies in the study mated with female fly carcasses that had died from the fungal infection between 25–30 hours earlier.

Only 15% of the males mated with female corpses that had been dead for three to eight hours.

Professor De Fine Licht said: "We see that the longer a female fly has been dead, the more alluring it becomes to males. This is because the number of fungal spores increases with time, which enhances the seductive fragrances.”

The study provides new knowledge that may lead to effective fly repellents in the future.

"Flies are quite unhygienic and can sicken humans and animals by spreading coli bacteria and any diseases that they are carrying. So, there is an incentive to limit housefly populations, in areas where food is being produced for example," De Fine Licht adds:

“This is where the Entomophthora muscae fungus may prove useful. It might be possible for us to use these same fungal fragrances as a biological pest control that attracts healthy males to a fly trap instead of a corpse.”

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