Large number of flies in our home

Observation by: David Russell

My name is David Russell and I am a student within the College of Health at the University of Alaska Anchorage. I have lived in the Matanuska-Susitna borough of Alaska for almost ten years now, residing in different parts of the borough during that time, but for the most recent three years my wife and I have lived in Northern Wasilla. I have observed the area within and surrounding our home during these past years for a variety of different reasons, including: to determine if a need exists for repair or reconstruction of facilities; to visually enjoy the scenery, and, most applicably; to be able to write observational reports for my science classes at the university. During the last three years, we have observed multiple different species of insect in the area surrounding our home, including different subclasses of spiders, centipedes, slugs, hornets, earthworms and mosquitos, to name a few. We had never before observed a species of the order Diptera, aside from the mosquitos present every year. Around the middle of September this year, however, there was a large influx of houseflies into our home. We determined the species due to the formation of their wings, in addition to the small antennae. This was not a gradual occurrence; on the 17th of September, there were no flies within the house or around the outside area. On the 18th of September, there were multiple swarms within the home, found specifically in the Living Room, Dining Room, Kitchen, Entryway and Garage. I observed that no flies were located outside of the home after this date either; only inside, in the previously mentioned rooms. There were also no flies in the second story of the home; each room on the second floor is used daily, but has a slightly cooler temperature. We searched for evidence of nests or items that may have attracted the flies inside (food, trash, feces) but we were unable to locate any. This corresponds to our patterns within the home; in the last three years, our habits have not changed as far as groceries/cooking and cleaning. We began to kill the flies through various means; most effectively by utilizing a hanging Fly Trap. We observed that as we removed the flies, no others entered to take their place, resulting in their swarms decreasing each time. We were finally able to remove all swarms and have found no trace of other flies in the area. This is the first year out of the three that we have lived here, where we have experienced any type of this species before. Could the drastically changing climate be affecting the reproductive timing or behaviors among insect species?

Derek Sikes with the UAF Museum writes: I would need to be able to study specimens of these flies to identify them below the superfamily Muscoidea. This superfamily includes a number of families, such as the Muscidae, and each family has hundreds of different species in Alaska. If we could identify the flies more precisely we might know their typical food source and that could help explain what they were doing indoors. The behavior is not too unusual however. Sometimes a food source, such as a dead vole, becomes a source of many flies that get indoors accidentally (usually looking for overwintering sites). Note that there is a species of fly called Musca domestica (aka the common house fly) but this species does not occur in Alaska an the flies in the photos do not match this species.