Stable fly
As summer approaches and we see the emergence of various species of flies, it is almost like an unofficial calendar. Cluster flies emerge from overwintering sites, followed by black flies around Mother’s Day, followed by stable flies and finally as summer ends, the return of the cluster flies, looking for overwintering quarters.
Each of these poses their own issues insofar as being a pest species, and we always have one of the species around and sometimes all three at the same time.
When we talk about overwintering flies, the two species that we commonly deal with are the cluster fly and the stable fly. The cluster fly feeds on earthworms and does not bite, where the stable fly is a filth fly and will bite us as well as livestock. Moose, deer, cattle, horses and humans are all targets of the stable fly.
It seems that both of these flies will seek shelter in our cabins and homes and when we see flies emerging indoors in the spring, we see both species to a varying degree. They don’t breed inside the walls during the cold weather but are just sleeping, waiting for the opportunity to make more flies as soon as weather permits.
Cluster fly
Stable fly
Basically, the stable fly is smaller, has a striped pattern on the area behind the head and is fast and agile. It is adept at feeding and getting out of the way when approached. Midsummer June through early August, it is the fly you are most likely seeing coming in through your open window or door.
An interesting thing happens with the stable fly. When warmer weather gets here and the winds turn to the south and west, stable flies are literally blown into the area from across Lake Superior from agricultural regions with lots of cattle (thanks, Wisconsin!). As I understand, the flies get pushed by weather systems and come across the lake with the wind at their backs at high altitude. Once over land, they descend in large numbers, and that explains why we will suddenly be invaded by a large number of flies where the day before there were few, if any. Some are always here, but many are imported.
Cluster flies
The cluster fly is typically the size of a housefly or bigger and generally is a darker color than a stable fly, which is slower and more easily swatted. It does not seek us out and will prefer to hang around the sunny window once inside in an attempt to get out. When at rest, the cluster fly will typically fold its wings along its body, giving it a more compact look rather than a triangular look that most flies exhibit.
After emerging from their overwintering sites in caves, cabin attics and walls, etc., they lay eggs in the soil and the emerging larva feed on earthworms. They go through three to four generations during the summer and we really don’t see them much until they gather to overwinter in early September, at which time they can be a huge nuisance. If you are seeing flies gathering on the sunny side of a building in large numbers in late August or early September, it’s going to be cluster flies.
Control of these flies is drastically different, and in this environment, we are always concerned about pesticide effects on both water and non-target species.
The stable fly can be moderately controlled with bait products, as spraying seems to be of little value. We use a combination of grain waste, fly bait and a touch of fish juice in a bait station to attract them and this seems to work within a smaller space out of doors. The bait is specific for flies and does not affect other pollinators, which is important.
With the cluster fly, bait is not an effective strategy and we approach control by treating the exterior of structures with a botanical repellant and sealing cracks and crevices to prevent overwintering. Flies will still get in during their swarm, but they will not be able to overwinter.
In any case, if you are having fly issues, there are probably solutions, except for the blackflies.
I am still working on that one!
Are bugs bugging you? Are you having problems with mice or ants or wasps or other creepy crawly insects? For help, call Bill Dalin, North Shore Superior Pest Management, Grand Marais, Minnesota, at 218-370-2323 or find him at NorthShoreSwat.com.
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