by Sally Colby
If your farm is attracting more than its share of flies, it’s because environmental conditions are just right. Dr. Gregory Martin, Penn State extension educator in poultry, helps livestock producers deal with fly issues, and says the first aspect of fly management is learning to identify them.
Martin describes the housefly as being one-quarter of an inch long with three main body parts, six legs and a striped thorax. “They’re the jets of the airplane world, with swept back wings when they’re at rest,” he said. “It’s important to understand the life cycle of houseflies to effectively monitor and manage them. They have four major life cycles: egg, larva, pupa and adult.” Martin noted that houseflies are tropical insects, and under ideal conditions with temperatures in livestock housing at 70 to 72 degrees, their complete life cycle is as short as 10 days.
A female housefly can lay as many as 30,000 eggs in her 30-day lifetime, and can travel up to a mile in the wind. Martin says a common complaint from homeowners in rural areas is never having flies until a poultry house is erected nearby. “The flies are in the environment, and then they go to the farm,” he said. “It’s like a burger stand — they’re going there because there’s something good to eat.”
The housefly has a spongy mouth and “blots” as it feeds on wet feed or manure. Martin says if the food source isn’t wet enough, the housefly will regurgitate just enough to solve that problem.
The stable fly is often seen on dairy farms and some poultry farms, and looks similar to a housefly. The noticeable feature of the stable fly is the proboscis, a “straw” that sticks out beyond its head and acts as a piercing mouthpart to penetrate hide.
“If you see a cow doing the Macarena, it has stable flies biting its legs,” said Martin, adding that sheep, goats and people are also bitten by stable flies. “They’re blood eaters, and diseases like encephalitis and West Nile virus are transmitted by blood-sucking insects.”
Martin says cows housed on straw or on bedded pack are often inundated with stable flies, which also congregate in damp drinking areas. He suggests watching for damp feed and other wet sources to limit opportunities for stable fly development.
“Calf pens are notorious for stable flies,” said Martin. “Calves are drinking milk for the first couple weeks, and the protein content of milk is very high. That high protein draws flies looking for a meal. Keeping a calf pen as dry as possible is important. If you can’t dry the manure, remove it so it doesn’t draw flies.” Martin noted that Cornell research on time budgets for calves indicated that calves spend significantly less time eating when fly numbers rise, which can be a limiting factor for weight gain.
A particularly nasty fly that seeks grazing cattle is the horn fly. “They bite like crazy with a narrow proboscis,” said Martin. “I’ve seen cattle run through pastures with horn flies on their backs. If you see an animal and its hide is quivering, they’re being popped by these flies.” Dust bags with repellant along with large roller brushes to work up the hair coat help repel horn flies.
Face flies resemble houseflies and are also known as lacrimal flies because they tend to accumulate around the eyes. Although they don’t bite, face flies are a vector of pinkeye and also transmit the nematode eye worm. Face flies are a bother to pastured cattle, and often cause cattle to seek shade rather than graze.
Bottle flies, also known as blowflies, are carrion eaters. Martin says he’s been on farms with improperly maintained mortality composting piles where rotting carcasses draw blowflies. “If you have blowflies around your composting area, add more carbon,” he said. “Proper composting will eliminate them.”
Martin suggests that producers think of fly management as IPM. “Make a plan, implement the plan, measure (through fly indexing) and review,” he said. “If we do this over and over again, the number of flies will go down.” Martin says many farms make two or three changes but they don’t know which change made a difference, while incremental changes will show the impact of each change over time. “In most cases, fly control is a numbers game and you’re in it for the long haul.”
Fly levels can be monitored with spot cards, standing sticky tapes, baited jug traps and moving sticky tapes. Martin says standing sticky tapes (ribbons) allow the producer to count the number and types of flies being caught. Spot cards are the most commonly used monitoring method and involve white 3×5 cards dispersed throughout a poultry house, barn or manure pit.
A manure spill or improperly spread manure can contribute to fly problems. “Make sure there’s an even flow or injection so it all dries and enters the ground at the same rate,” said Martin. “In hot weather, manure will dry pretty fast. It helps if you can harrow the field to break up the clumps. If you go to the field and see lines of manure that fell off the spreader or there was something wrong that caused it to be spread unevenly, those are issues.”
Cultural methods such as removing manure, drying manure and other measures that maintain moisture levels below 40 percent help with fly control. Cultural control starts with good building design and good ventilation. “Moisture control is about 90 percent of fly control,” said Martin. “If you have a water leak, fix it as soon as you find it. In many dairy farms combatting mastitis, some is due to too much moisture in the bedding, which also contributes to flies.”
Physical controls can help manage humidity, which helps limit fly development. Turn compost piles frequently, especially in summer, to kill eggs and larvae. Chemical controls should be a last resort — they’re expensive, and if overused, result in resistance. Martin suggests careful tracking of active ingredients in chemical products to lessen the risk of resistance. Some producers have success with biological controls such as blister beetles and parasitic wasps, but it’s important to use a full-season program for best results.
Martin often deals with issues that arise when non-farm residents notice an increase in fly populations due to neighboring farms. He says it’s important for people to realize that manure is part of the farming ecosystem and important in a nutrient program for crops, but it’s also critical that farmers work with neighbors and avoid spreading manure prior to neighbors’ picnics and other events.
“See it from the eyes of the person watching you,” said Martin. “People smell with their eyes. If you have a sloppy-looking operation from the road, they won’t think as highly of you as if you kept things nice and neat. Tell your story explain what you’re doing and why you’re doing it. Most of the time they’ll get it.”
Additional housefly monitoring program information is available at