Cluster Flies

This past week at the Bolt Hole we first experienced a hard frost with the morning temperature dropping to the upper 20s and then had several days of 75 to 80 degree highs. This resulted in the annual infestation of Cluster Flies.

Now, I’m not sure how wide spread this phenomenon is (but the search I did using Google produced returns from Penn State, U of Kentucky, Iowa State, Virginia Tech, Canada, and Ohio State and that was just on the first page!), I only became aware of it after I had purchased the Bolt Hole and met with several other folks in the Hunter Mountain area of NY. For those of you who do not know what I’m talking about, cluster flies (I’ve also heard them called “buckwheat flies”) look like house flies but they are a dull, drab gray—to-black fly not the iridescent green and blue flies you see feeding at your sugar bowl. In fact, I’m not sure adult cluster flies feed at all.

As fall approaches, the angle of the sun in the sky decreases and the nighttime temperatures drop closer and closer to freezing. Then the cluster flies will start to gather on the sun drenched walls of the cabin. The search is on for any nook and cranny that offers itself. They’ll invade your house (or any warm, protected spot) in the fall of the year with the intention of toughing out the winter in the cracks, crevices and corners of your home. Masses of their tiny bodies may huddle together to conserve energy. In an unheated building like a shed or barn, this isn’t a problem.

It’s in a heated building that they become nuisances. Even if the heat source is panes of glass on the south side of the building, it might be enough to rouse them from their winter torpor and make them think spring has arrived. This, in turn, will set them upon a search for an exit to the great outdoors and, not being too bright, they end up buzzing around on the glass windowpanes and doors in huge numbers. When night arrives and things get cool again, they may slip back into any convenient crack. Of course, if you’ve turned up the heat or built a fire in the stove for your personal comfort, they’ll continue to enjoy the warmth, too. But without an exterior source of light to attract them, they’ll start to buzz around the light bulb in the lamb; rattling and smashing into the light shade as they do so. Like a said a nuisance.

Apparently, preventing their entrance into your home is the best bet at control. But it’s not easy. They can squeeze through the tiniest of cracks and any old home will have lots of places for them to get in. There are dusts ad sprays that can be applied before the infestation starts but once it has occurred, it’s best to forget the insecticides. Carpet beetles may feed on the dead bodies and they can do damage to a multitude of fabric materials in your home. No, I find the vacuum cleaner to the best tool at controlling the flies in the winter. On a sunny afternoon, when they gather by the dozens hundreds on the south facing glass, I‘ll just spend a few minutes hoovering them up. They may not die in the vacuum bag but they can’t get out easily either. Especially if I‘ve also vacuumed the spider webs out of the corners and the rug.

In searching for information about cluster flies, I learned that the larval stage is a parasite of earthworms. That is one of the reasons they are so numerous where healthy, moist soils and lawns exist. I’ve got a sizable lawn around the Bolt Hole and an overgrown field across the road. Portions of both are shaded from the sun and stay rather moist from either dew or runoff. The cabin, however, is painted dark brown and portions of it are exposed to sunlight which it absorbs quite well.

On a side note: Last fall, when Terry was living full time at the Bolt Hole we didn’t have a sizable infestation of cluster flies. I don‘t think the three cats had anything to do with that but they did enjoy chasing down the few errant flies that came within their reach. I do know that the lack of any fall infestation meant there were far fewer flies all winter and into the spring.

Learn more here:

From Penn State: CLUSTER FLIES Pollenia rudis (Figures, they’re illegal aliens:

Cluster flies are thought to be native to Europe and may have found their way to North America in the ballast of ships containing soil and the cluster fly host, earthworms.

From Iowa State: Cluster Flies
From Canada: Effective Control of Cluster Flies

From Virginia Tech: Cluster Fly

Isolated houses in the country are especially prone to invasion, since they offer the only warm shelter for miles around.

Fits the Bolt Hole to a T.

I got just one question: Where did they live before man started building homes?