Last November I was getting out of my van, glanced down, and saw something odd clinging to the underside of a rusted metal bar at ankle height. It was a housefly, apparently stuck to the metal by its mouthparts.

If you noticed that my last few days of posts have all been about Cordyceps, you might guess that this was the result of a parasitic fungus, and you’d be right.

Entomophthora muscae (formerly Empusa) is an obligate pathogen of flies, in a good range of families. It’s difficult to keep viable in the lab, and colonies can only be maintained by infecting fresh flies. Victims survive 5 days to a week as the fungal hyphae invade every organ. Then they are forced to land, and to start crawling upwards, and attach themselves to a surface with sticky saliva, spread out their wings and legs, and promptly die. After that, the fungus erupt from every joint in the abdomen - the white fuzz in the photo - and the spores are fired out into the surrounding countryside. The wings and legs are held out the way for just that reason.

If the spore lands on another fly, good for the fungus, but it has a another trick up its sleeve - if it doesn’t find a host immediately, the spores wait a few days and sprout into a simple tower, grow more spores at the end, and have a second chance at infecting a host. According to some sources, sometimes these secondary spores manage a third go, before any food reserves are exhausted.

Funnily enough, the Fly Destroyer is quite vulnerable to high temperatures, so I wasn’t expecting to see it in an Australian summer, as happened with here. In fact, infected flies can cure themselves of the infection by resting in hot areas.