Everyone knows the old joke in which a restaurant diner asks, “Waiter, what’s this fly doing in my soup?” But considering the regulatory, health, and customer relations nightmares flies can cause, flies are no laughing matter to anyone whose job is to ensure food safety.

Populations of houseflies and some other flies reach peak levels in late summer, so this is a good time to take steps to prevent fly problems in food processing and foodservice facilities.

Fly Behavior

The feeding behavior of flies makes them ideally suited for spreading disease-causing bacteria and parasites: they may feed or lay eggs on garbage, animal manure or other filth outdoors and, seconds later, land on open food or food contact surfaces indoors. When they do, they immediately begin transferring disease agents – by direct body contact; by vomiting on the surface (flies are not capable of ingesting solid food; they must regurgitate saliva onto their food, and lap up the digested liquid); and by their fecal deposits. The potential to transmit a variety of human illnesses is very real.

From a regulatory perspective, the need to prevent fly activity in the food processing environment is clearly spelled out in the Food, Drug and Cosmetic Act: “A food shall be deemed to be adulterated if it consists in whole or in part of any filthy, putrid or decomposed substance [or] if it has been prepared, packed or held under conditions whereby it may have become contaminated with filth, or whereby it may have been rendered injurious to health.” Under this definition, regulatory action can be taken against a food processing company if insects, parts of insects, or the contaminants they carry, are found in or near ingredients, finished products, or processing equipment – whether or not actual contamination occurs.

The standards of non-governmental inspection agencies such as AIB also require conditions within processing, packaging and storage areas that are free of uncontrolled insect activity. Failure to take action against fly infestations can result in a failed sanitation/GMP inspection – and, ultimately, in the loss of customer confidence.

There is one more reason for taking flies in food plants seriously: The same conditions that can be identified as sources of fly problems can also be the source of microbiological concerns. In other words, the presence of putrid and filthy material in an area can give rise not only to flies, but to fungal and bacterial growth as well.

Needless to say, food processing and handling facilities are attractive to flies because they provide food, attractive odors, warmth and an abundance of moisture. Flies have little trouble getting inside, since doors are opened frequently to receive ingredients and packaging materials, to ship product, and to allow employees in and out. Bright lights inside and over doors attract flies and other flying insects from great distances.

Types of Flies

There are two general types of flies that may have to be dealt with – small flies and large flies. Large flies, including houseflies, bottle flies, face flies, and flesh flies, usually can be traced to a source outside the building. Typically, they breed in garbage, animal manure, dead animal carcasses, and other rotting material such as wet grain spillage. Small flies, including small fruit flies, small dung flies, phorid flies, and moth (drain) flies, usually come from a source inside the building.

They breed in fermenting liquids (small fruit flies), poorly cleaned drains (drain flies), sewage (phorid flies, drain flies and dung flies) and rotting food debris (phorid flies and dung flies). Insect Light Traps (ILTs) use ultraviolet light to attract flies and other night-flying insects, including some stored product pests. They are available in two varieties – electrocuting ILTs, which use an electrical grid to kill insects attracted to them; and glueboard-type traps, which attract flies and then trap them on a sticky surface.

Electrocuting ILTs are, as a rule, larger and more powerful, but glueboard type traps are more suitable for installation very close to food-contact surfaces or open-food zones. ILTs serve both a monitoring and a control function. Using them only as glorified bug zappers misses the point of their real value as tools to continually assess whether flying insects are present; what kind of flying insects are present; and where they are coming from. A trained IPM specialist can “read” the catch pan of an ILT in order to identify sources of pest insects, and head them off before they become a major problem – or cause a failed inspection.

It is important to have enough ILTs in place, and that they are situated near critical entry points in such a way that they do not attract flies indoors from outdoors – and they do intercept flies as they enter – if possible, before flies make it to sensitive areas. A detailed treatise on ILT placement is beyond the scope of this article; however, a Copesan IPM Specialist can provide counsel on effective placement of ILTs.

Plant management must adopt the attitude that fly management is important and possible; and a knowledgeable pest management professional must perform the tasks of careful observation, inspection, identification of the flies involved, and implementing the correct control measures. With consistent cooperation and effective two-way communication between PMP and client, there’s no need to worry about flies in the soup.

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