Did you know that zombies lurk in the forests and hedges of PEI? Fortunately for us, these aren’t the pop-culture creatures from ‘Night of the Living Dead’ (or – worse – ’28 Days Later’) and they’re not after human flesh or brains. They are true flies (Dipterans) infected by Fly Death Fungi (Entomophthora muscae complex, Photo 1).
Mind-controlling fungi may seem like the stuff of science fiction or video games, but they’re real. The most famous is Ophiocordyceps unilateralis (aka Cordyceps or Zombie Ant Fungus), which is known mostly from tropical regions. Our temperate-region Fly Death Fungi function in much the same way and it is truly fascinating.
Spores of Fly Death Fungi land on a healthy fly and within a few hours germinate and begin to penetrate the insect’s outer covering (the cuticle). Once inside, the fungi get into the Fly’s ‘blood stream’ (technically the hemolymph) and over the next week or so consume much of this fluid and the internal organs. The fungi then take over the critically ill insect’s brain and nervous system and cause it to ‘summit’: climb to an elevated spot and spread out its legs and wings as shown in the photo. Once in position, the fly dies; the fungi bind it to the leaf and within a few hours release spores, starting the cycle again. Forcing its host to an elevated position helps spread the fungal spores, just like dropping a handful of dust from shoulder-level versus ground-level.
I usually find these zombie flies on the undersides of leaves about 150 to 180 centimetres (five to six feet) off the ground, though in fairness those are the ones around eye level that I am most likely to spot. They’re common along trails, hedgerows, and woodland edges across the Island and I do enjoy pointing them out on my field walks and talks.
These fungi aren’t huge fans of heat, so you are more likely to find them in late spring and early summer and again in the fall rather than in the dog days of July and August. Fly Death Fungi attack many different species including House Flies (Musca domestica), so you may be lucky enough to watch this drama unfold in your own home! Unfortunately, House Flies have developed an adaptation to these fungi, and will move to a warmer location to inhibit their growth. While there has been some work to develop Fly Death Fungi into a natural, biological control for Dipterans, this has been unsuccessful to date.
Fly Death Fungi are unquestionably cool parts of PEI untamed!