There’s no need to travel to exotic rainforests to find mind-warping parasites. They are probably lurking in your own backyard.
That, at least, is where Carolyn Elya found a “zombie fungus” that takes control of fruit flies. She took it back to her lab, where she managed to get it growing in lab fruit flies. “It was incredibly lucky,” she says.
So-called parasitic fungi are well-known in the insect world. They usually infect their host, before controlling its behaviour to give it the best chance of spreading to more victims.
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Seeing a similar fungus attacking fruit flies should help us learn more about how they operate. Because so much is known about fruit flies, as they are one of the standard animal “models” studied in labs around the world, Elya’s team at the University of California, Berkeley, has been able to find out much about the fungus in just a short time.
“It’s really cool just to work what’s going on, but we may also learn general principles about how it changes behaviour,” she says.
It might also help in the hunt for treatments for brain diseases like Alzheimer’s, says David Hughes of Pennsylvania State University, whose team studies other zombie fungi. “It’s wonderful to have this now in a fully trackable model,” he says.
The fungus, called Entomophthora muscae, kills fruit flies in four to seven days, Elya’s team has found. The animals appear to behave normally until the final day, when their gait becomes shaky and they won’t fly even if prodded.
Death pose
Instead, they start walking up any vertical object and soon stop walking altogether. The flies then extend their proboscis and use it to “glue” themselves to whatever surface they are on. Over the next ten minutes they slowly spread their wings in little bursts. Then, a few hours before sunset, they die in a characteristic death pose.
It was this pose that allowed Elya to spot the infected wild flies. “Their wings were stuck up at a particular angle,” she says.
After the flies die, the fungus starts sprouting from their bodies. “By the end of the infection ,” tweeted team leader Michael Eisen in a thread describing the discovery.
Five hours after sunset, the fungus starts to launch tiny sticky spores at high speeds (9 metres per second). To film the process, the team had to use cameras that take 54,000 frames per second. The spores can be propelled several centimetres, Elya says.
So how does the zombie fungus take control of the fly? Elya has found that the fungus invades the nervous system very early on, appearing first in the brain after around 48 hours. However, it does not appear in the same brain regions in different flies. So she think the fungus alters behaviour by releasing chemicals directly into the brain.
If this is confirmed, it would be a different mechanism to the way the cordyceps fungus takes control of ants. This fungus leaves the brain alone and instead grows around muscle fibres and appears to take control of them, Hughes’ team reported in November.
“In our case, we are finding that it’s more like a marionette pulling strings,” says Hughes. But as Cordyceps are not at all closely related to E. muscae, that’s no surprise. “It’s absolutely guaranteed that the mechanisms are different.”
Indeed, zombie fungi and other mind-bending parasites could turn to control their victims in many different ways. There are lots of them out there, and only a few have been studied so far. “There are a ton of these fungi that infect different insects,” says Elya.
Journal reference: bioRxiv, DOI:
