Seven Tips for Effective Management of Blow Flies

7. Dead insects: When insects die, their bodies start to decompose, providing nutrients for other organisms in the ecosystem.

It is true that blow flies typically overwinter as fully-grown larvae, which then pupate before emerging as adults in the spring. However, the black blow fly (Phormia regina) is an exception to this pattern. It is known to overwinter in the adult stage in temperate regions (Dondero and Shaw 1971, Roberts 1930, Siverly 1972, Wallis 1962). Overwintering black blow flies will seek out warm and protected areas such as attics or crawlspaces to overwinter. These areas may include attics, crawlspaces, or other protected spaces within buildings.

Blow flies are also important in forensic investigations, as their life cycle and behavior can be used to determine the time of death in a human or animal corpse. However, pest management professionals (PMPs) are concerned about blow flies because their presence often indicates the presence of a dead animal, typically a mouse or squirrel, which is a potential health hazard and can cause unpleasant odors. Blow flies can also be a nuisance in outdoor areas where people gather, such as parks and outdoor dining areas. Consequently, blow flies can be an indicator of a larger problem and require a comprehensive fly management approach to effectively manage fly infestations and prevent future ones from occurring. Here are seven tips for the effective management of blow flies:

(1) Identifying and removing breeding sources. Identifying (inspection) and removing blow fly breeding sources (Sanitation) is a key component of non-chemical control methods and can affect effectively fly populations. If only a few blow flies are seen indoors, it may indicate that they have gained access through an open door or window from an outside breeding site. In this case, efforts should be focused on identifying and removing outdoor ding sources such as animal manure, carcasses, and decaying plants. Because blow flies are attracted to decaying organic matter, it is important to inspect and identify any rotting material sources that may attract the flies. The presence of a large number of blow flies indoors can indicate the presence of a dead animal or decaying organic matter in a nearby area. This could be in a wall void, garage, attic, chimney, or crawlspace. Locating and removing the source of the decay is essential in eliminating the breeding site and reducing the blow fly population.

(2) Fly-proofing the structure. Fly-proofing practices are important for managing blow fly populations because they help prevent adult flies from entering buildings or areas where they can lay eggs and create breeding sites. Blow flies are attracted to decaying organic matter, such as animal carcasses, garbage, or compost, and they will lay their eggs on or near these materials. The eggs will hatch into larvae, which then feed on the decaying material and eventually pupate and emerge as adult flies.

By implementing fly-proofing practices such as screening windows and doors, installing air curtains, keeping doors shut, sealing gaps, and installing door sweeps, it becomes more difficult for adult blow flies to enter buildings or areas where they can lay eggs. This can help reduce the number of breeding sites and limit the population of blow flies.

(3) Trapping. Traps can be used to capture and kill adult flies. There are several types of traps available, such as sticky traps, light traps, and bait traps. These traps can be placed in areas where fly activity is high, such as near garbage cans, compost piles, or pet waste areas.

(4) Mechanical control. Using fans or other devices to create airflow can help deter flies from entering buildings or certain areas. In addition, fly swatters or electric fly zappers can be used to kill adult flies.

(5) Pesticides. If there are still large numbers of flies present regardless of implementing the abovementioned practices, limited spot treatments using residual insecticides can be applied to manage breeding areas and resting places for adult flies. Additionally, if the infestation cannot be tolerated by the customer, space treatments can be used to quickly knock down the adult flies. It is important to follow label directions for both efficacy and safety measures when using insecticides. This includes removing all people and pets from the area being treated and covering all food processing surfaces and utensils. After treatment, it is recommended to wait for the holding and aeration periods specified on the product label before returning to the treated area.  

Fly baits can be registered for use in and around breeding areas and hard-to-reach places to attract and kill flies. However, it is important to read the product label before using bait and to follow any usage restrictions or safety measures. For example, baits must be placed out of reach of animals and people, and spray drift should not come into contact with animals, water, or food preparation and feeding areas. If the drift is going to contact non-target organisms, they should be removed before treatment if possible, or the bait should not be applied. It is also important to note that fly baits should not be used inside food processing or manufacturing facilities, as well as in classrooms or patient rooms, to avoid attracting flies to these sensitive areas.

Treating blow flies that overwinter in a structure can be similar to treating other fall invader pests. The goal is to prevent them from entering the structure in the first place by treating all possible entry points, such as under eaves and around rooflines. When treating a structure for overwintering pests such as blow flies, it's important to pay attention to the areas where the pests are likely to enter the building, such as high entryway rooflines, soffits, and rooflines. These areas provide access for the pests to enter the attic or crawl space, so it's essential to treat these areas thoroughly to prevent entry. Additionally, it's important to pay attention to the sunlit sides of the building, as these areas tend to be warmer and may be more attractive to pests seeking a place to overwinter.

(6) Monitoring. Regular monitoring can help track the effectiveness of the control methods used and identify any changes in fly populations over time. Insect light traps (ILTs) are a valuable tool in monitoring the presence of adult flies, including blow flies, indoors and can help guide targeted control efforts to manage and reduce populations. These traps use ultraviolet light to attract adult flies, which are then trapped on a sticky surface or electrocuted by the trap.

By regularly monitoring the number of flies captured in the ILT, it is possible to predict adult flies' population levels and frequency of occurrence. This information can be used to develop a targeted control plan, which may include non-chemical control methods such as sanitation, exclusion, and removal of breeding sources, as well as chemical control methods if necessary.

It is important to place ILTs in areas where adult flies are likely to be found, such as near garbage cans, compost piles, or pet waste areas. It is also important to regularly clean and maintain the traps to ensure that they are working effectively.

ILTs can be particularly useful in large indoor spaces, such as commercial kitchens or food processing facilities, where blow flies can be a serious health and sanitation concern. By regularly monitoring the presence of adult flies with ILTs, it is possible to detect and address infestations early, before they become a larger problem.

(7) Keep records. keeping records can be very helpful in tracking the effectiveness of control methods and identifying changes in fly populations over time. It allows you to monitor the number of flies caught in traps, the location and frequency of sightings, and any changes in breeding sources. This information can help you determine which control methods are most effective and make adjustments as needed. Keeping records can also be useful in demonstrating compliance with regulations and providing documentation for future reference. It is important to maintain accurate and detailed records to ensure that you can track the success of your efforts and make informed decisions about future control strategies.