I remember growing up in a house that had its share of what I always called basement bugs and playing with the sow bugs on the basement floor. And in the late winter there were always two harbingers of spring— the first ladybug and those flies that seemed to come out of nowhere.
I didn’t understand it at the time but both of these critters had actually arrived five months earlier and were now just responding to the increase in length of day and temperatures. The fly emergence in the house was sometimes epic and I remember Mom vacuuming up hordes of the flies as they made their presence known. It was always a mystery as to the source.
It is now many years later and having been a pest control operator…(aka “Bug Man”) for going on 30 years I feel like I know these little guys pretty well.
To understand cluster flies you need to know why they do what they do.
Emerging in the spring from, you guessed it, our homes, they mate and then lay a large amount of eggs on an unsuspecting host— earthworms.
Those spring rains that drive earthworms temporarily to the surface assist the cluster fly in accessing them. When the worms go back into the soil they are the unsuspecting carriers of the next generation of cluster flies whose eggs hatch into worm-feasting larva and then pupate and emerge in June/July as flies. The wetter the year, the more eggs are laid.
As a relatively new arrival to Cook County, I experienced the full force of black flies and no-seeums for the first time this year and can say that by comparison the cluster fly is a pussycat. It is not really a biting fly and it is not a garbage fly for the most part. It does, however, know how to throw a party and invite all of its friends!
Come mid-August, nighttime temperatures start to go down and we start a slide toward fall. It is at this time that cluster flies begin to scope out their overwintering quarters. Gathering (“clustering”) in large numbers on exterior areas of the home, around eaves, dormers, window casings and any crack that may lead into a dry overwintering harborage, cluster flies start to enter our homes. By mid September they normally have made their way in and go into a dormant stage that is similar to hibernating. If you have not done anything to prevent them from getting inside by then you just arm yourself with a flyswatter and wait.
What can you do to reduce them?
I have always been a promoter of longterm and non-chemical solutions to pest issues. Cluster flies can be kept out by the use of caulk around cracks that lead into wall voids. An inspection of your home’s exterior will reveal, in many cases, hundreds of potential openings and sealing them is a great idea. The cluster flies just have to go somewhere else, so pull out the ladder and caulking gun and go to work. Keep in mind that cluster flies will normally seek out cracks and entry points high on a building…not at the foundation.
Or, if you want to use a pest management firm to help, there are a number of companies that use botanical repellants that work very well, and if applied in late August or early September, can effectively prevent the flies from entering this year. It breaks the cycle of the flies entering your home and that also seems to be important.
And that’s the rest of the story…
Bill Dalin of Grand Marais, owner of North Shore Superior Pest Management, shared this interesting insect information with Cook County News-Herald readers.
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