MOSA provides our clients with much more than just certification.

Joe Pedretti

MOSA Client Services Director

Organic Fly Control Options

Organic Fly Control Options

By Joe Pedretti, Client Services Director

Not all flies are parasites, but there are several species that do bite and feed on the blood of domesticated animals, and can, if their num­bers are high, cause economic losses. Parasitic flies also can cause severe discomfort.

Horn flies are about half the size of house flies, are dark gray and have piercing mouthparts. They are blood-sucking flies that stay on the shoulders and backs of cattle almost continuously. During extremely hot weather or when it rains, they may move to the protected underside of the animal.

Source: Michigan State University

Stable flies are sometimes called biting house flies due to their similar appearance. Stable flies feed primarily on legs and lower abdomen of cattle by penetrating the skin and feeding on the blood two to three times a day depending on the weather. Once full, they move to a resting place, usu­ally in the shade, to digest their meal. The blood loss and pain associated with the bite of stable flies results in substantial economic loss.

Source: University of Kentucky

Deer flies are black or dark brown in color, about the size of a house fly, and can be recognized by their triangular shape and bright red or green eyes. Horse flies are very similar to deer flies, but are sig­nificantly larger. Only the females need to feed on blood. They do this to obtain the nutrition needed to lay eggs. Both deer flies and horse flies have an aquatic life cycle where the eggs are laid in marshy, wet areas and the larval stage develops in these wet soils. Because of this complex life cycle, they are very difficult to control.

Fortunately, deer and horse flies are mainly a nuisance pest, and do not occur in large enough numbers to inflict substantial physical damage. Still, they are highly annoying to livestock. They use scissor-like mouthparts to slash open a wound to drink the blood. Their saliva prevents blood coagulation, and creates a histamine reac­tion (large swelling at the bite). For this reason, livestock often stop eating to seek refuge from deer and horse flies.

Preventive Control Options for Flies

Sanitation and manure management are key to controlling horn and stable flies. Clean out pens, exercise areas, feed bunks, hutches and stalls frequently (minimum 1x weekly). These flies will breed in spilled, wet feed, so do not neglect areas under bunks and in other feeding areas.

Muscovy ducks are well known as voracious eaters of fly larvae and pupae; chickens are also a good option. A small flock allowed to patrol outside pens and around hutches can bring down fly populations. Some farmers are follow­ing their cattle with chickens in the grazing rotation to pick through cow patties to reduce fly numbers.


Research has shown that animals deficient in certain minerals are more attractive to parasitic flies. Feed free choice minerals, especially these critical traces: Copper, Sulfur, Iodine. These should be at high levels in your mineral mix and can help offset deficiencies and make animals less palatable to blood-feeding flies. There is also some evidence that free choice apple cider vinegar provides animals some resistance to biting flies.

Active Control Options (Adult Fly Control)

Put up fly paper and fly tape in the barn, and keep it fresh. Tape and paper lose stickiness quickly due to dead flies and dust. Tape rolls make it easy to expose fresh tape.

Fly trap barrels work extremely well. A clever design by organic dairy farmer Kevin Jahnke expands and improves upon the idea behind smaller scented fly traps. Kevin takes 55-gallon plastic barrels and cuts a rectangular square in the top and glues in a clear piece of plastic or plexiglass. Around the perimeter of the barrel, about halfway up on four sides, he cuts holes and inserts plastic PVC tubing with 90 degree elbows pointing towards the bottom of the bar­rel. He then fills the barrel with about 8 inches of water and “scents” the trap with rotting food and manure. The flies enter the trap through the PVC tubes, smelling a nice environment to lay eggs, but instinctively fly up towards the light and cannot escape, eventually dying in the trap. These can be placed anywhere on the farm, including grazing paddocks. Learn more here:

Epps Biting Fly Trap™

The Epps Biting Fly Trap™ kills about one pound of biting flies daily.

In a three-year study conducted by Cornell University, the Epps Biting Fly Trap™ killed an average of one pound of biting flies each day. The trap requires no electricity, chemical or messy baits—it uses just soapy water. The trap mimics the color and outline of cattle and horses, which attracts biting flies. They hit the trap and drop into the soapy water where they cannot escape. Then they drown. They can be bought online through several sources including:

Walk-through Fly Traps

Walk-through traps, also known as the “Bruce Trap” after the entomologist who designed it, have been around for a long time and have proven to be cheap, easy to maintain, and very effective at reducing horn and stable flies. The walk-through trap is placed in a lane that all animals must pass through on their way to and from the pasture or other communal area. Hanging strips of canvas, plastic or other flexible material brush the flies off the animal’s face and back. The trap has two layers of screen­ing on the outside walls with small, one-way holes between them. The flies instinctively try to escape by going towards the light, and get trapped between the two layers of screening.

The trap was designed for cattle, but can be modified to accommodate smaller ruminant animals. Most animals are reluctant to pass through the trap at first, so some training will be necessary. Detailed instruction can be found through the University of Missouri:

Biological Controls

Biological controls are an important part of any integrated pest control program, and one that all organic producers should consider. A combination of good cultural controls (sanitation, traps, nutrition) and biological controls are often effective enough that additional inputs (sprays, oils, etc) are not even needed. Natural enemies of insect pests, known as biological control agents, include predators, parasites, and pathogens (fungi, bacteria, viruses). Biological controls can be purchased and applied during the season to help control parasitic flies, especially flies that breed in manure like horn and stable flies. Parasitic wasps have proven particularly effective and work by killing the larvae and pupae in the manure.

Several tiny, parasitic wasps attack immature stages of flies. The wasps insert their eggs into the immature stages of several species of flies. The wasp larvae feed inside the host and eventually kill it. The wasp completes its development, emerges as an adult and continues the process by searching out more hosts. These small wasps only attack flies, they do not sting or bite animals, or humans.

A popular choice is “Fly Eliminators” from Arbico Organics: or call 1-800-827-2847

You can also buy fly parasites from companies such as Kunafin (, and Rincon-Vitova (

If your cultural and biological controls don’t provide enough relief, you may need to look into repellent and insecticidal sprays. Please note, these products will be “Restricted Use” and you will need to update your Organic System Plan and Input Inventories. Always call MOSA before using a new input.

Repellent Sprays

Aromatic essential oils will repel flies (and gnats, which are also from the fly family). The challenge is to apply the oil to the top and under­side of the cow with enough coverage to repel flies. It will have to be reapplied frequently. Spraying the animals right after milking in the morning is a good strategy. Some farmers keep a small pump sprayer in the parlor and give them a shot on top and underneath after milk­ing. These oils also can be added to oilers and brushes so cattle can reapply it themselves.

Several companies make good, ready-made, essential oil repellents. Here are a few we have reviewed:

• Fly Repellent (Crystal Creek)

• Shoo-Fly Concentrate (Dr. Sarah’s Essentials)

Insecticidal Sprays and Oils

Natural pyrethrin sprays can be sprayed on animals to kill flies or on problem areas where they congregate. Be careful however, many of these sprays contain compounds like piperinyl butoxide that are prohibited for use in organic production. Pyganic™ is a favorite because the oil base gives it longer activity. Sprays for flies are considered “restricted use,” meaning that you can only use these insecticides if your other control methods have failed to give sufficient control.

Special Note

Always confirm the status of any new live­stock product with MOSA before use. Some “natural” products may contain synthetic or natural ingredients that are prohibited in organic production. Most “allowed” products are actually “Restricted Use.” So ensure that MOSA is aware of the change to your input list and to your Organic System Plan, and that you are using the product for its intended use. Follow all label instructions and consult your veterinar­ian when serious health problems are apparent.