Out, out flies!
Not so long ago, a delicious lunch at an upmarket restaurant in a grand arcade was marred by a few unwelcome feeders. All it took was a few flies to downgrade the place in the eyes of our group. The waiter who came along with an electric fly swatter failed to whet our appetite.
But then, my home is not exclusive of flies either. Ordinarily, they are nowhere in sight. But let a visitor settle down, bring out a fruit juice, and they gate crash. It’s more than annoying to have a fly in your bonnet when there’s a guest under your roof!
We know houseflies carry dirt, but we tend not to regard them with the horror we reserve for pests like the dengue mosquito. Yet their bad habits, like vomiting and defecating on the food they land on, can be harmful. Since their menu ranges from faeces and rubbish to fresh fruit, they ingest all types of germs and transmit numerous diseases, including cholera, gastroenteritis, tuberculosis, conjunctivitis and E-coli. After an outbreak of E-coli in a school in Japan, the same pathogens found in human sufferers were found in flies in the school kitchen. Some estimate that a single fly can carry as much as 33 million micro-organisms in its belly. All it takes for a fly to become a carrier is a few seconds on a contaminated object, and a single visit to your plate.
Flies are both an urban and a rural problem,” says Raja Mahendran, consultant to global pest control organisations. “They are a problem in hotels, restaurants, cafes, food processing plants, dairy facilities for cattle, pigs and poultry, where animal excreta serves as an ideal breeding ground for flies. They carry diseases to animals as well, and the nuisance they create decreases animal and worker productivity.”
They are survivors
Flies belong to the vast order Diptera (true flies) which also includes mosquitoes, midges, gnats and sandflies and counts over 200,000 species. There are hundreds of different types of troublesome flies – the flesh fly, that large striped grey fly, that prefers faeces and dead flish, the green and blue bottle fly, fruit flies and stable flies that also bite and suck blood. There’s another smaller cluster fly that also likes blood. Unlike many other insects, flies use just one pair of wings (diptera means ‘two-winged’) for flying. Like most household pests, they are survivors. Their huge compound eyes see much more than we do – they can perceive 200 separate pictures per second compared to our 60. And they are extremely difficult to swat because, like fighter pilots, they can speedily manoeuvre their way out of danger by performing sideway jumps, spirals, and somersaults in the air.
The average female house fly lays about 600 eggs in her lifetime, usually in rotting materials such as garbage dumps. Folks who toss garbage bags onto the sidewalk and poor public garbage management policies help them to proliferate. Manure and animal excrement are also favourable breeding sites, which is why you find them on farms. It can take just a few hours for the eggs to hatch, and soon the larvae (maggots) feed and pupate very quickly. After a few days, the adult emerges and mates. Flies breed faster in warm wet climes, which is why some places swarm with flies in July.
Three trouble makers
In Sri Lanka, three fly species give us grief: the house fly, the stable fly (the large striped one) and the fruit fly. Every year, fruit harvests in Sri Lanka suffer substantial loss annually due to fruit fly attacks.
The best approach is exclusion and sanitation. Install fly screens and air curtains, and speedily dispose of garbage,” says Mahendran. “Store garbage in air tight containers, and keep food covered. Keep interiors clean and position fly traps, and spray directly on to adults outside. In short, deny them food and shelter.”
Larvae are the bigger part of the problem. “As with mosquitoes, fly maggots and pupa are the 80 percent of the problem not addressed. Flies lay eggs on organic material, dung, moist soil, food scraps, and, yes, on garbage. That’s why they are hard to control,” Mahendran says, adding that dipterex, the fly larvicide used locally, is no longer available in Sri Lanka as registration was not renewed and new products have not been introduced.
Nothing is all bad, and there’s an upside to flies: They recycle food waste and hasten decomposition of carcasses. Without them, frogs, lizards, spiders, bats, dragonflies, fish and birds would be hungry and closer to extinction. Some flies pollinate flowers, and in fact, places that do not have bees rely on flies for pollination. Gardeners will be delighted to learn that hover flies, a fly species found globally and in mid-country region of Sri Lanka, feeds on aphids during its larval stages.
Further, maggots are seriously considered to aid decomposition in waste management. And since flesh flies, blow flies and bottle flies are the first insects to land on dead animals, forensic entomologists use them to pinpoint time of death of murder victims. Maggot therapy, the use of maggots to control wounds, has been practised for over a century and is still considered a viable option for healing today, using contamination-free flies bred in laboratories. Maggots in a wound only consume dead tissue, never living tissue.
The war against flies
The fly-swatting waiter at that restaurant had not been briefed on an important point: electric fly racquets tend to splatter fried fly parts around, and into your food possibly. In the West, they are banned from use in food production areas, says Mahendran. Similar and less conspicuous devices that use UV lighting to attract flies and glue to destroy them are discreetly positioned in eateries.
The pest control market offers a range of products; from fly bait that affects the insects’ reproductive cycle, some even making males sterile, to aerosols that can kill adults instantly. In some places, biological control methods like the use of predatory insects like parasitic wasps that feed on fly eggs are used.
Problem outdoor areas like an open fish market would be difficult, says Mahendran, unless a huge area around it is made free of all breeding sites. But an indoor market can be controlled by installing air curtains at entrances, fly screening at other openings, and electric fly killers. An open food cart would be a challenge in the tropics, he adds. To get around the problem, install a glass enclosure.
At home, I try to be kind to little creatures. In addition to fly screens and general cleanliness, there’s an arsenal of natural ingredients one can use to deter them: cloves stuck into an apple or lemon, because flies are said to be averse to the combinations of the two aromas. Fillng clear plastic bags with water and hanging them in places flies tend to congregate is another solution. Flies have about 8000 lenses in each eye, which make them ultra sensitive to movements of light. Since water reflects light in every direction, flies tend to stay clear of the bag and the area.
It is also said that flies are attracted to twilight, so if your house has a fly infestation, open the windowns at twilight and they will fly out. Remember however that that’s also the time the mosquitoes fly in.