Management & Control of Flesh Flies

Cover Story - COVER STORY

Flesh flies generally do not infest structures in large numbers or with any regularity, but when they do will you be prepared?

June 5, 2019

Stoy Hedges

Editor’s Note: The following article is excerpted from the soon-to-be-published 2nd Edition of the PCT Field Guide for the Management of Structure-Infesting Flies by Stoy Hedges.

Most of the efforts to control flesh flies involve preventive measures and non-chemical control methods. The pest professional’s job is to discover the causes of the infestation and to make control recommendations.

SANITATION. The first goal in managing flesh flies — when they are entering from outside — is to minimize or eliminate the conditions attracting the flies to the building, and this is a customer-oriented task. Customers who fail to address exterior sanitation will most likely have more significant fly issues.

Flesh flies have a checkerboard-like pattern on top of the abdomen.

Proper handling of trash and regular cleaning of dumpster and trash is critical in minimizing flies near a structure. Disposing of food garbage in plastic trash bags before placing in a dumpster is also helpful.

Keeping the dumpster area clean attracts fewer flies to the area. Regular cleaning also eliminates potential breeding sources near the building. If the dumpster is too close to a building, the flies that are attracted to the garbage are closer to the delivery entrance or loading dock. More flies could then enter the building than if the dumpster was located farther away. Dumpsters and trash receptacles should be located as far from the building as possible (i.e., across the parking lot or access pavement).

EXCLUSION. Cracks around doors and windows where flies are entering should be sealed with a long-lasting sealant. Doors and windows need to be kept closed when not in use unless they have proper screening installed. Doors also need proper weather stripping around all edges of the door, especially in the center where double doors come together (seen on many commercial buildings).


AIR DOORS. Some commercial buildings may equip one or more exterior doorways with air doors to help exclude flies and flying insects. Air doors require regular maintenance and adjustments to ensure they can exclude insects from the top of the door to the ground.

While the air door is engaged and on, hold a piece of paper near the top of the doorway and lower it all the way to the ground. If at any point the paper starts to veer back into the building, it means that outside air pressure or breezes are overriding the air stream put out by the air door, allowing insects to be sucked into the building. In such cases, the air door will need adjustment.

Flesh fly, Sarcophaga spp.
Stoy Hedges

FLY TRAPS. Traps such as the EZ Trap can be useful in some situations to capture flesh flies. Figure 1 on page 24 shows an EZ Trap placed in a storeroom of a pet store that has captured dozens of flesh flies. In this case, roof rats killed by snap traps in the false ceiling were the source of the flies. Not only do dead rats or mice in traps need to be removed regularly, but rodent exclusion and control efforts will be necessary to help prevent future issues with flesh flies (or blow/bottle flies).

INSECT LIGHT TRAPS (ILTs). Flesh flies may manage to enter the building despite the best sanitation and exclusion efforts. ILTs are highly effective in attracting and capturing flesh flies and serve as a 24-hour “sentinel device” in removing adult flies all day, every day (when they are properly maintained).

Typically, the greater the fly issue, the more ILTs that likely will be needed. Larger structures also will need more ILTs. The type and style of ILTs used will vary by location in the building and is something to discuss with the customer based on their needs and their budget. Mixing in smaller traps such as the FlyWeb and GLOstik with standard glueboard ILTs (back of house) and sconce ILTs (front of house) can be helpful.

FLY RESTING AREAS. Surfaces where flesh flies land to rest are key sites to apply residual treatments to help kill flies before they enter a building. Focus on areas such as the sides of dumpsters, the walls of dumpster enclosures and walls around doorways.

Flies landing on these surfaces to rest will be killed thus helping to reduce flies near buildings. A number of residual insecticide products have flies listed as a target pest for outdoor applications and CS or SC formulations generally work well. Follow label directions for best results.

Figure 1. Flesh flies trapped in large numbers on an EZ Trap. Inspection revealed the source to be dead rats trapped by snap traps in the ceiling.
Stoy Hedges

ANIMAL CARCASS SITUATIONS. A sudden appearance of flesh flies inside will typically resolve itself in a few days as emerging adult flies will die. Customers, however, are unlikely to want to wait and will desire efforts be made to find the source if possible and to control/remove adult flies as they emerge.

The best way to remove flesh flies is through use of ILTs, and the FlyWeb ILT is ideally suited for capturing these flies in a timely manner. FlyWeb ILTs plug into any 110V outlet and can be installed in one or more rooms where flies are most visibly seen. The traps can be left in place for several days, then retrieved, or the traps may be sold to customers for their own use.

Where flesh fly issues are related to an attic, false ceiling, crawlspace or basement, one or more larger, glueboard-style ILTs may temporarily be installed in the affected space.


INSECTICIDE TREATMENTS. Because flesh flies will be attracted to windows, a thin spot treatment of a residual insecticide or labeled fly bait may be applied in corners or along the sill of windows. Flies contacting treated surfaces will be killed. The EndZone Insecticide Sticker also may be placed as detailed on the product’s label.

The author is a Board Certified Entomologist and president of Stoy Pest Consulting.