It’s inevitable. Just as you allow the embrace of the couch cushions, and succumb to the siren call of a mid-winter afternoon nap, just as your eyes finally close and your entire body relaxes, you hear it. Bzzzz….. bzzz….bzzzzzzzzz….the intermittent buzz of cluster-fly wings against your window, demanding your renewed attention to the world around you, most likely in search of a fly-swatter.
“They drive people crazy,” said Tom Hooten, CSU Extension agent for Montezuma County. Cluster flies, known by the Latin name pollenia rudis (rude indeed!), are native to Europe, and believed to have been introduced to North America by ships carrying soil as ballast. They have since colonized the continent, and like their human carriers, brought their way of life with them.
“Cluster flies are not what is known as a filth fly,” Hooten continued. “They’re not associated with garbage or spoiled products. Cluster flies are primarily found at higher-altitude environments, and forested environments.”
They feed on earthworms, so in fact, “cluster flies are a good sign that you are in a very healthy environment,” Hooten said.
Adult cluster flies lay eggs in openings in soil, and when the larvae hatch, they find and burrow into live earthworms. The cluster- fly maggots look much like any other common fly maggot — short, fat, cream-colored, and slightly wedge-shaped. Eventually these maggots go through a final pupation stage, and morph into flies. They can produce several generations each season.
According to Hooten, the adults move into homes when it gets cold, looking for shelter. “When it warms up, they cluster, around lights, around windows…they love windowsills.”
They begin their habitation of your house innocuously enough, just taking up space under your siding, in your attic, or in cracks, crevices, and voids in sheds, garages, or barns. But then, on a warm day, they get confused. They are drawn like disco fiends to the disco ball, seeking out the nearest beacon of light shining through the nearest crack.
They thread themselves through your interior light fixtures, through the tiny gaps in your windows, through the spaces between your trim and floor. They sneak into your home en masse, evoking scenes from “The Amityville Horror,” and gather against every pane of glass that brings light into your home. They hurl their bodies against the glass, trying with all their might to get outside and into the light, to no avail, smearing the glass with their fly vomit, and exhausting themselves to a lengthy, drawn-out, buzzing death.
Meanwhile, there you are, innocently trying to nap, wishing with every new sound that you could rid yourself of this plague once and for all. The good news is, they don’t carry pathogens the way typical house flies do, but that’s hardly consolation for a tired soul on his or her couch. “There is no magic bullet,” Hooten confirmed.
You might try chemicals, but you would be foolish to do so. Since the flies enter your home from the outside, and congregate primarily in spaces not used by humans, it’s usually hard to get to all the places they inhabit.
If you do succeed in killing them with sprays or dusts, carpet beetles and other insects descend to eat their carcasses, and subsequently prey on your own woolens, stored dry goods, and other natural products in the home. Plus, Hooten added, “it’s not a good idea to use pesticides inside the house, especially around kitchens.”
He said, “For the preventive side, there is nothing better than to work on sealing the house.” Use sealing materials to keep them from getting in, both on the exterior and interior of your home. Use screens, weather stripping, and caulk around exterior entry points. Use caulk on the inside around light and duct fixtures, around window and door trim, around baseboards, around wall and floor outlets, around any type of crack and crevice small enough for a fly to pass through into the areas of your home that you inhabit. This might also help you keep your home warmer, by decreasing drafts that enter through these same minute openings.
“Of course, this work needs to be done in the fall, before they enter your home,” Hooten said.
But you should know that the best efforts of mice and men can only go so far, and if you live anywhere that earthworms live, you can expect some cluster flies to get into your house. And according to Hooten, “The easiest way to control them when they’re in the house is to vacuum them up.”
Make it a daily habit to go around to all your windows and suck up as many living and dead flies as you find. This will diminish their populations immensely, although it won’t stop new flies from entering your abode. That’s why you do it daily.
And don’t be surprised to find flies actually flying out of your vacuum — keep it running for 60 seconds after you’ve sucked up the last fly to discourage this devious behavior.
You can also hang adhesive fly traps in your windows, although clean-up can get messy. If you have an attic space, you can leave a low-wattage light on which will attract the flies and cause them to use up their stores of energy and die. Then simply sweep up the pile of fly carcasses.
Most importantly, know that you are not alone in this frustrating reality. The flies are not the result of poor housekeeping, they are not related to any nearby sources of garbage or compost, nor are they linked to any haunting. They are simply insects, doing what insects do best.
Melissa Betrone writes from Dolores, Colorado, where she cultivates a population of Venus fly traps.