The most significant and economically important pest to dairymen is the biting stable fly. It is often referred to as the beach fly, dog fly, lawn mower fly and other names, some not printable. They attack most mammals, including cattle, horses, sheep, goats, swine, dogs and humans. If you have flies feeding on your cows’ legs or flanks, causing them to be nervous and constantly stomp and switch, you probably have a stable fly problem that is costing you money.

At the University of Nebraska (2007), stable flies depressed calf weight gains by 0.48 pounds per day and yearlings by 0.44 pounds per day. These same populations also significantly reduced milk production.

The stable fly adult is Âź-inch long, has seven circular black spots in a checkerboard fashion on a gray abdomen and a cutting-sucking proboscis (mouthpart) that protrudes in front of the head, like a beak or bayonet. The adult cuts the skin to feed, causing a painful bite. They will stay on the host for two to five minutes and normally feed only once per day during the daylight hours. After a meal, they will seek a vertical surface such as the side of the barn, fence or weeds to rest. Since the digestion time after a blood meal is much longer than the feeding time, the numbers of flies at one time on your animals are only a small percentage of all those present. Their habit of resting on vertical surfaces plus the beak in front of the head makes them easy to distinguish from a non-biting house fly, which does not have a protruding proboscis. The adult fly will normally be found feeding on the legs (especially front legs), belly, sides and back of larger animals but seem to prefer the legs, head and ears of their smaller hosts.

Stable flies will develop in straight cow manure but much prefer decaying organic matter such as wet, spilled feed, hay (especially high-protein round bales), protein supplements, distillers grain, decaying grass, soiled bedding, etc. A mixture of manure, urine and bedding such as in a calf hutch provides a very productive stable fly breeding area. In a research study done by Texas A&M, it was estimated that over 1 million stable flies developed in the remaining waste left over from each round bale that had been left undisturbed from the winter feeding.

A female stable fly may lay over 1,000 eggs, which hatch in one to three days with the newly hatched larvae burrowing down below the surface to avoid desiccation. To find the breeding areas you must scratch a few inches below the surface. Fully developed larvae crawl to drier areas to pupate. This accounts for the extremely high numbers often found near a post or edge of the bedding pack or silage pile. The life cycle of the stable fly is three to four weeks. At temperatures near freezing, the larvae survive by delaying development for 90 to 120 days. In the northern climates, this is considered the normal overwintering method and occurs in areas that generate moderate amounts of heat during the winter. Normally, 90 percent of the flies will develop in 10 percent or less of the area. If these areas can be identified and eliminated, or dried out, fly numbers will be greatly reduced. Examples would be piled silage, manure piles, bedding packs, etc.


Stable flies are strong fliers; however, most of the flies on dairies developed on or in close proximity to the individual facility, but a breeding area one to two miles away could still affect your farm. Stable flies become a major problem in early spring. Numbers tend to decrease when it gets hotter and drier, then another smaller explosion in numbers occurs in early fall with cooler temperatures and moisture.

The economic impact of the stable fly is very significant. Cattle irritated by the blood feeding flies will consume less feed, grow more slowly and convert feed into milk or body mass less efficiently. A secondary problem is that the animals crowd together to avoid the feeding flies and then heat stress becomes an issue. Animals will spend much of their time stomping, tail switching and throwing their heads to try to rid themselves of this pest. Milk production will be reduced when heavy stable fly populations are present. Research shows that 72 percent of the production loss from stable flies is caused by animal behavior (bunching) and 28 percent is attributed to the stable fly feeding.

There is no one single thing that will eliminate the stable fly problem. In order to manage them, we need to use all the tools that are available. Chemicals are generally one of the first things many consider, but resistance has developed to a large number of the currently available products, with very few new products entering the market. Check with your local extension specialist, farm adviser or licensed pest control operator to determine what products can legally and safely be used that will provide control in your area. Always read and follow the label directions. With direct animal treatment, application should be applied to the animal’s legs to reach the major fly feeding areas.

Residual treatments of pesticides to fly roosting areas can be effective but after a layer of dust collects on the surface, it will often prevent the fly from encountering the pesticide. Direct sprays and fogging of breeding sites may be counterproductive as they have a damaging effect on parasitic wasps and other naturally occurring beneficials such as mites, earwigs, ground beetles, etc. While the emerged pest flies will disappear for a short time after spraying, approximately 90 percent of the fly population during the warm months has not yet emerged and is unaffected by sprays. In a few days the flies are back, worse than ever as the natural controls have been eliminated.

Sticky tapes and baits are not effective for stable fly control. Although some flies may be caught on the tapes, there is no attractiveness to them except the vertical surface for resting. There are many house fly traps on the market but only two traps that attract the stable fly. Be sure and check the label to determine if it attracts this pest.

Sanitation should be the first item on the list for any fly control program. Remove the moist breeding areas or spread the material thinly to dry it. Proper sanitation combined with a parasitic wasp release program will generally provide satisfactory stable fly and other pest fly management. Combining appropriate use of insecticides with the aforementioned measures may be needed to rapidly reduce an outbreak of adult stable flies. PD

For direct questions, you may contact Dr. Bill Clymer, senior scientist with Spalding Laboratories at

Bill Clymer