April 08, 2021
When I was making dinner last night, Melissa called and asked me to come look at our front screen door. I had noticed earlier in the afternoon that the screen seemed to have black specks all over it. We have a cold front coming in and it brought along 10 to 15 mile per hour winds. Since it was windy (for Arkansas) and having just mowed the grass, I though that must be what was all over the screen. When I checked on Melissa’s request, I found the specks were about 50 small flies that had spread across the entire screen. I have never seen anything like this before and could not imagine what caused them to gather. I thought of getting the fly swatter but figured they would just come inside if I opened the door. I left them alone.
When I looked online, I found these were probably either “grass” or “cluster” flies (Pollenia rudis). The typical cluster fly is about 7 mm long and can be recognized by distinct lines or stripes behind the head, short golden-colored hairs on the thorax, and irregular light and dark gray areas on the abdomen (I did not get that close to look). Cluster flies are typically slow-moving and are completely harmless to human health. They are instead strictly parasitic on earthworms. The females lay their eggs near earthworm burrows, and the larvae then feed on the worms. Cluster flies seek refuge in cold weather and find their way into attic spaces and similar areas indoors. They often emerge on warm days, and cluster at windows (hence the name).
While the article spoke of the flies coming into the house through the attic or small cracks in the house, ours were instead clustered on the outside of the house, although I do not know where they wintered. Since the flies “cluster,” they can become a nuisance when they gather in the attic during the winter or when the warm weather brings them outside in March or April. While there are a variety of chemicals to control them, the best way is by mechanical exclusion. Since they are hibernating when they are in the house, and sluggish even when they are not, the site suggested you might use a mini vacuum to catch them. Seriously, this is something you just cannot make up.
Thoughts: I found it interesting that every site I found online about cluster flies concerned how to get rid of them. While a few did contain information about the flies themselves, every one of them recommended ways to eliminate the flies. This was more interesting as the sites all confirmed they were not a threat to humans. They just slowly go about their business of propagating and laying eggs in my yard. If I were a worm, I might be worried, but since I am human, there is no reason to be concerned. Other types of flies are not only a pest but also carry disease and some even bite, but not cluster flies. We have lumped these flies in with all the others because they look similar and gather in large groups. We tend to do this with people as well. Rather than getting to know them as individuals we group them together and discount them all. We need to recognize the value of individuals rather than discredit perceived traits of groups. Do the work. Change is coming and it starts with you.