I like to point out to people that leaves have two sides and when those leaves are growing close to the ground, you have the opportunity to examine both sides. In general, highly mobile creatures are more likely to be found sitting out in plain view such on the upper leaf surfaces. Creatures with greater vulnerability are typically more hidden, like on the lower leaf surface. It’s interesting to watch someone scrutinize the upper surface of a low hanging cluster of leaves, but never make an attempt to view the hidden surface.
Turning over a leaf is like scratching off a lottery ticket. The back side of this Black Walnut leaf made me the big winner.
I don’t know if it’s more proper to say that this was a fly or that this is a fly. There are certainly some recognizable fly parts remaining, but there’s a lot or stuff there that’s definitely not fly. That yellowish mass is a fungus that has consumed most of the soft body portion of the fly. That doesn’t sound like such an awful fate for a dead fly, but in this case, the fungus began its work inside the fly body while the fly was still living.
Many insect species meet their ends at the hands, or mycelia, of pathogenic fungi. All it takes is the spore of the proper species to make contact with its intended insect host. The fungus grows inside the host, first attacking non-vital functions so the insect continues to be active. Eventually a time comes when the host succumbs to the ravages of the fungus and dies anchored to some leaf or stem. The fungus completes its life cycle and spreads its own spores to the wind.
Many accounts attribute the fungus with the ability to control the host’s behavior. As a final act prior to death, the host is compelled to head to a high, open perch. Supposedly this position affords the fungus with the greatest chance of spreading its spores on the passing winds. I question if that’s true in all cases. The fungus victims I typically come across are usually in a location considered normal for that particular species. This fly for instance, was on the underside of a leaf; a normal place for many flies to spend the night. I’ve also found fly fungus victims atop plant stalks, but this too is a normal position to find flies. I’ve probably found just as many in positions low to the ground, so it just appears that they die where ever they happen to be when that time arrives. I can just imagine a group of mad scientists out there feverishly trying to unlock the mysteries of fungus mind control, but I’ll hold on to my skepticism until I see a little more substantial evidence of its existence.
Regardless of the many possible interactions between the fly and its fungus, it’s just plain fascinating that so many species of fungi are all floating around looking for their own specific host insects. All this was found beneath one small leaf. Imagine what the rest of the tree has to offer. If you’re interested, TheBug Geek made a nice post about a moth that suffered a similar fate to this fly.