Preserving Our History: Flies, Flies, and More Flies

By Patrick Kelley, ACE

The earliest warming days of spring through the hot summer and into the chilling autumn, flies continue to plague commercial businesses, homes, and museums alike. Of the more than 110,000 species of flies on this planet, most are not considered pests and some are quite beneficial. A few, though, can cause emotional and economic stress as well as propagate disease. Each different type has its own unique environment in which it will thrive. In order to eliminate the flies, we need to remove the source of their existence. Once we have identified the pest, our job to eliminate it becomes much easier as we can then know what environment this particular fly comes from. There are several species that I come across quite frequently in museum settings. Here are the top 5 with some tips on identification and elimination.

House Fly, Musca domestica: This is likely the most common fly worldwide. House fly adults have 4 dark stripes on the thorax and are 7 mm in length. They commonly infest the places where people live and spend time. They can be found breeding in anything from spoiled food to manure. The key to control is sanitation and exclusion.

Moth Fly, Psychodidae: This distinct looking and relatively small (3 mm) fly has the appearance of a moth because its entire body and wings are covered with hairs. Moth flies primarily breed in drains or sewer pits, feeding on gelatinous organic material. The key to control is to eliminate their food sources in the drains by thorough cleaning and an application of microbial foam that breaks down the bio-gel.

Common Fruit Fly, Drosophila melanogaster: Restaurants and food sales in museums are very commonplace, as the revenue and enjoyment that the visitor’s experience is essential. Unfortunately, fruit flies commonly come into the building closely behind the food. They will feed on spoiled fruit and vegetation as well as the sugary drinks at the soda fountain. Removal of their food sources and rotation of produce is essential. Traps can keep the large numbers down on this small 3 mm fly.

Fungus Gnat, Sciaridae: These slender flies can look a little like a miniature mosquito at 2 – 6 mm in length. They are commonly found in office spaces and anywhere else where live plants are kept. These flies live and breed in soil where they feed upon the fungus and moist organic matter. They will thrive under certain soil conditions if the plants are being over-watered and the soil is constantly wet. Control is possible if the plants are removed or if the soil is allowed to completely dry and treated with diatomaceous earth.

Cluster Fly, Pollenia rudis: This fly is medium in size (7-9 mm) and can come into structures in large numbers during the months of August and September. Yellow hairs on their upper thorax help identify them from other flies. Eggs are laid singly in the soil outdoors and the emerging larvae will locate an earthworm and bore into it. This parasite will feed on the worm for 3 weeks before pupating. They look for man-made structures to over-winter. The best control method is preventing them from being able to enter your building. If they do get inside, light traps can be very effective.

References: S.A.Hedges, “Field Guide for the Management of Structure-Infesting Flies,” G.I.E.Inc., 1998
Photo credits: 1. House Fly: Copyright ©2009 iNaturalist, BugGuide.net 2. Moth Fly: Sarah Faulwetter, Encyclopedia of Life
3. Fruit Fly: Michael Ashburner, Encyclopedia of Life 4. Fungus Gnat: Copyright ©2005 Richard Leung, BugGuide.net 5. Cluster Fly: © Thomas Murray – BugGuide.net

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