The majority of people eating in a restaurant would go back to eating their meal after a fly touched and contaminated it, but almost no one would touch their food after seeing a cockroach crawling on it. The same kind of attitude is seen in staff and managers in the food-processing industry (“It’s just a fly, wave it away”), and it can cost them their business.
When the authorities shut down a local restaurant or a food processing unit, it’s usually because of rodents or cockroaches – seldom is the “innocuous” fly the reason a restaurant goes out of business. And yet, according to entomologists, filth-breeding flies (a term referring to several species of true flies of the order Diptera, including the four subspecies of Musca domestica, the house fly) are at least twice as filthy as cockroaches.
Due to their abundance (uncontrolled, they would cover the whole planet 18 inches deep in just one season), their close association with people, and their ability to transmit disease, filth flies are considered a bigger threat to human welfare than most other household or commercial pests. Flies are known to transmit about one hundred animal and human pathogens, but emerging research shows they may be even more dangerous than we previously thought. Some of the most common diseases spread by flies include:
In many cases, adults with a good immune system are able to fight off the disease agents in food contaminated by flies. However, children, elder citizens, and people whose immune system has been compromised by illness or medication are far more exposed to the health hazards posed by pest flies.
In Canada, about 4 million people (1 in 8) are affected by food-borne diseases, which result in 11,600 hospitalizations and 238 deaths every year. These staggering numbers are even greater than those in the U.S., according to a food safety report published by the Conference Board of Canada, which also suggests that half or more of all food-borne diseases in the country are picked up at restaurants, cafeterias, and other food-service providers.
The pathogens carried by flies enter food through one of two ways: (1) direct incorporation of the filth they carry on their bodies and (2) the contamination of food and food-contact surfaces by the microorganisms and metabolic products released by flies while feeding and defecating.
Understanding the ecology of flies helps to explain their role as vectors of disease and allows an efficient selection of control measures. Flies breed, feed, and wallow around in decayed, fermenting, or rotting organic material of either animal or vegetable origin. Among the most important breeding sites for flies are heaps of accumulated animal feces, garbage and waste from food-processing plants, organic manure, sewage, and accumulations of rotting vegetable matter.
After landing on a potential food source, the fly first vomits its gut contents on to the food. Lacking chewing mouthparts with teeth to help them masticate food into tiny, digestible bits, it must use its sponge-like tongue to liquefy any solid food it comes about. To this purpose, the fly brings up regurgitated food and saliva and uses it to dab the meal with digestive enzymes that will gradually turn solid food into liquid the fly can then slurp without much effort. In doing so, flies may also regurgitate bits of human or animal excrement.
Since they vomit repeatedly, flies also need a lot of fluids to stay hydrated, and the need to defecate increases exponentially in relation to the quantity of liquids consumed. They produce feces once every few minutes, passing the remaining bacteria and pathogens in their digestive system on to food for human consumption. Some microorganisms can remain in the mouthparts or esophagus for several days and then be flushed out on food with the next salivary flow or defecation.
The body of a fly is also structurally adapted to pick up pathogens from filth and waste. Its mouthparts are covered by many fine hairs and ridges that readily collect germs and bacteria. Its tarsi have a complex structure of hairs and sticky pads that further enhance the fly’s potential to act as a mechanical vector for diseases.
For food-service providers faced with fly issues, the cost of control is minuscule compared to the negative impact and losses incurred through infestation. Food and food-surface contamination caused by flies can increase exponentially within a brief period. In ideal conditions with unlimited resources, a single fly can defecate up to 50 times in 24 hours. In just two weeks, a single fly can lay more than 1,000 eggs, and each of the future adult flies will be able to carry as many as one million bacteria on its body.
Establishments impacted by fly infestations can face significant fines and even temporary or permanent closure by the public health department. But even more terrifying than the financial and health-related aspects is whether or not your fly issue will go public. Many public health authorities post inspection histories online, and a growing number of media outlets are making sure this information is disclosed to the public.
Word-of-mouth – the primary driver of any business’s success – can become your worst enemy in the aftermath of a fly infestation. According to a recent poll of food-service customers, 60% of restaurant patrons would tell five or more people about a pest sighting in a restaurant, and a quarter of them would write a negative review or an email about the incident. Considering that more than half of frequent restaurant diners factor online reviews into their dining decisions, each review you get can have a lasting impact on one out of two customers in one of your key demographics.
Client cooperation is important in just about any pest control program, but it becomes essential when dealing with fly infestations in commercial accounts. In lack of chemical control methods similar to those used to control pests such as rodents or cockroaches, sanitation, along with regular inspection and exclusion, becomes crucial in all fly management.
Understanding environmental conditions necessary for growth and development in relation to controlling pest populations is the first priority. Food attractants, food-contact surfaces, and materials on which flies can lay their eggs must be eliminated from the premises, destroyed as a breeding environment, or isolated from the egg-laying adult.
The frequency of sanitation protocols is also essential in controlling fly populations. Considering that the house fly completes its life cycle within 10 days, removal of necessary environmental conditions should be conducted twice a week in order to break the breeding cycle. Garbage cans and dumpsters should have tight-fitting lids, be emptied regularly, and kept as far from the premises as is practical. Waste and decaying animal or vegetable matter should be promptly removed, while areas with excessive moisture should be kept as dry as possible.
Exclusion, another important step in controlling pest fly populations, is achieved by keeping doors, windows, and vents closed or properly fitted with screens, and by sealing and caulking other access points that flies use. Air curtains or automatic door closing mechanisms can be installed over doorways to impede flies from entering the premises.
The best way to keep flies far from your commercial establishment is to be one step ahead of them, and this cannot be achieved without making pest management a part of your staff’s duties. Through regular communication and cooperation with your pest control provider, your employees can be taught how to properly inspect incoming shipments, report any signs of pest presence, clean up residues, and identify pest-prone areas. Keeping your premises clean is at the heart of food safety and customer experience, and staff education is key in ensuring that no fly will make its appearance in or contaminate your products.
About the Author
Daniel Mackie, co-owner of Greenleaf Pest Control, is a Toronto pest control expert well-known as an industry go-to guy, an innovator of safe, effective pest control solutions, and is a regular guest on HGTV. Mackie, along with business partner Sandy Costa, were the first pest control professionals in Canada to use detection dogs and thermal remediation for the successful eradication of bed bugs. In his free time, he is an avid gardener.