The three fly species most commonly encountered in Missouri commercial settings — drain flies, fruit flies (phorid and Drosophila), and house/blow flies — have completely different breeding sources, different management approaches, and different indicators of where to look. Misidentifying the species and applying the wrong treatment approach is the most common reason fly programs fail to resolve commercial fly complaints.
Three Species, Three Sources
Drain Flies (Psychoda spp.)
Drain flies breed in the organic biofilm that accumulates in floor drains, under equipment with poor floor seals, and in any standing water with organic accumulation. The characteristic moth-like appearance — small, fuzzy, triangle-shaped wings — distinguishes them from fruit flies. Treatment requires physical removal of the biofilm through drain cleaning with enzymatic products applied to the drain surface, not pesticide spray. Adult drain flies in a commercial kitchen almost always indicate neglected floor drain maintenance.
Fruit Flies and Phorid Flies
Small brown flies hovering near drains, bar areas, and produce storage suggest fruit fly or phorid fly activity. Fruit flies (Drosophila) breed in fermenting fruit, vegetable residue, and the beverage residue in bar drains. Phorid flies breed in a wider range of organic material and may indicate a more serious source — failed drain traps, a drain line leak, or decomposing organic material in a wall void or under a floor slab. Phorid fly infestations that persist despite drain treatment warrant investigation of the drain line itself.
House Flies and Blow Flies
Larger flies (house flies, blow flies, bottle flies) entering a commercial facility in significant numbers typically have an outdoor breeding source — exterior dumpsters, receiving dock waste, or an organic material accumulation near the building. Perimeter exclusion, exterior baiting, and air curtains at entry points address interior entry; eliminating the exterior breeding source stops the population. D&D Pest Control provides commercial fly programs for Franklin County and rural Missouri — visit ddpestcontrolmo.com.