Fly Control

Fly control strategies for cattle and horse owners


Flies are among the most difficult pests to control. Some species of flies, including horn flies and stable flies are blood feeders. These biting flies can cause serious economic losses every year. Non-biting flies are also problematic, as they carry disease and can be very annoying for both livestock and humans. As rural areas are increasingly encroached upon by urban sprawl, nuisance lawsuits (which consider house and stable flies together) are also on the rise. This type of litigation usually cites dust, odors and flies as a complex without identifying particular fly species. Urban growth into agriculturally-zoned areas has expanded the likelihood of lawsuits, which simultaneously increases the cost of liability insurance. If lawsuits are settled in favor of the claimant, the settlements require either punitive damages or the removal of livestock. With this in mind, it is no wonder that fly control is of vital importance to today’s savvy cattle and horse owners.



Some common flies that should be known by cattle and horse owners are face flies (Figure 1), stable flies (Figure 2), house flies (Figure 3) and horn flies (Figure 4.). Horn and face flies cause problems in pastures, and house and stable flies are problematic in and around barns and stables.

Horn flies

Adult horn flies are about half the size of house flies. They are dark gray in color, with two transparent wings that fold flat over the back, often in a delta position. The horn fly’s life cycle is completed in 8 to 45 days, depending on temperature and humidity. Horn flies account for the majority of the fly problems encountered by our customers. These flies can be distinguished by their habit of congregating and resting, head down, on the back and shoulders of their host animal. Whereas other flies always seem to be on the move, horn flies tend to rest quietly until disturbed. Depending on the weather, horn flies will rest on different parts of the host’s body (e.g., on the underside during intense heat or rain) or on light or dark-colored patches of hair (dark patches during cool temperatures; light patches when the weather is hot). Horn flies rarely leave their host, except to lay eggs, to move onto other cattle in the herd or when cattle enter buildings. Each fly may feed 10 to 38 times each day, causing not only annoyance and irritation to the host but also, when flies are present in greater numbers, the loss of up to one gallon of blood. As a result, grazing time is disrupted, leading to significantly reduced weight gains and daily production. Horn flies can also quickly spread bacteria and disease from one animal to another. The horn fly is thought to be responsible for an estimated $700 million in annual losses for the U.S. beef industry alone. Studies have shown that the annoyance, irritation and blood loss caused by flies can reduce the weaning weights of calves nursing from fly-infested mother cows by 12 to 14 pounds. Additionally, the average daily gain of grazing yearling steers can decrease by 12 to 14 percent, or as much as 30 pounds, during the grazing season. Horn flies can also depress the sexual libido of bulls, leading to reduced reproductive efficiency.

Stable flies

Stable flies are dark-colored, ¾ of an inch long and have piercing mouthparts that extend from underneath their heads. They resemble the common house fly, apart from their mouthparts and the "checkerboard" markings found on the underside of their abdomens. Their life cycle lasts around three weeks in the summer and longer than that in cooler weather. The females deposit 400 or more eggs during their lives. Stable flies feed on most species of domestic livestock but are major pests for horses and cattle. They penetrate an animal's skin with their piercing mouthparts and feed on its blood. Stable flies primarily feed on the animal’s front legs, causing groups of animals to bunch in a circle as they all attempt to protect their front legs from flies.

Face flies

Adult face flies are similar in appearance to house flies, except for being larger and darker. Face flies are serious pests to both cattle and horses. They are nonbiting flies that feed on animal secretions, nectar and dung liquids. Adult female face flies typically cluster around the animal’s eyes, mouth and muzzle, causing extreme annoyance. Since they are so active around an animal’s eyes, face flies serve as vectors of eye diseases and parasites, such as pinkeye and eyeworms. They are also facultative blood feeders, meaning that they gather around wounds caused by mechanical damage or biting flies to feed on blood and other exudates. They often overwinter in homes and other structures near pastures where these animals are kept.

House flies

House flies are similar to face flies in their appearance and their ability to develop in similar material, although the house fly will also develop in fresh manure. Because house flies have sponging mouthparts, they cannot pierce the skin of an animal. Instead, they feed on animal wastes, decomposing feeds and other liquified organic matter. The life cycle of the house fly lasts around two weeks. House flies are thought to be responsible for the transmission of many animal and human diseases.

What can livestock owners do to control flies?

Controlling fly pests in and around pastures and barns requires an integrated approach, as no one fly control method or insecticide product will result in total control. For flies to be able to reproduce, they require the appropriate breeding material, optimum moisture and adequate warmth. As such, eliminating any of these elements will also reduce the fly's ability to produce a new generation. A successful fly control program must include:

  1. Sanitation
  2. Mechanical control
  3. Proper use of insecticides

Sanitation should be the top priority of any fly control plan. Manure and other organic fly breeding material should regularly be removed from barn and stable areas and disposed of by being spread evenly over pastures. Another method is to compost the manure and bedding. The heat generated by a properly maintained compost pile will kill fly eggs, thereby reducing fly populations. Additionally, be sure to clean up spilled feed and other organic materials to prevent the creation of additional fly breeding grounds. Reducing moisture in pasture and paddock areas can also reduce the likelihood of fly development. Corrals and working areas should be designed to promote adequate drainage and eliminate wet spots. Automatic waterers in or around the barn should be properly maintained to keep moisture from spreading. If this sanitation is not maintained, chemical control may be unsuccessful.

One of the most common means of mechanical control is the use of screens. Screens do a good job of keeping flies out of barns, but their downsides include the additional cost of installation and their subsequent maintenance. Many people are also familiar with electric bug zappers and jug traps; while these options can help eliminate flies, they do not usually provide satisfactory control when active fly breeding is taking place.

Finally, even with good sanitation and mechanical control practices in place, flies can still become a problem — which is why insecticides are important for any fly control program. Insecticides can be delivered to livestock through insecticide-impregnated ear tags; self-treatment dust bags and oilers; animal sprays; pour-ons; or feed additives. These methods all come with advantages and disadvantages, but insecticides are generally necessary to round out a complete fly control plan.

SWEETLIX® fly control options

The SWEETLIX brand of supplements offers several fly control options to be added to a mineral or protein supplement. For the best results, applying fly controls from the last frost in the spring through the first frost in the fall is recommended. The generally best dates to begin application are shown in the figure below:



SWEETLIX offers three fly control additives: Altosid® IGR and ClariFly®. A brief overview of each additive and product is listed below.

Altosid IGR

Altosid IGR (insect growth regulator) is an additive that targets only the horn fly. This insecticide mimics a hormone in the fly that stops those flies from becoming adults and, as a result, from biting and sucking the blood from the host. Altosid is only labeled for use in cattle and is not approved for use in horses. An illustration of the cycle through feeding a supplement with a fly control additive is included below.


The newest fly control additive is ClariFly. ClariFly is similar to Altosid as it is also a growth regulator that stops flies from maturing, but it is also similar to Rabon in that it targets all four flies — horn, face, stable and house flies — and is approved for use in both horses and cattle. Available SWEETLIX products with ClariFly include:

Are SWEETLIX fly control products safe?

Yes: research has shown that Altosid IGR and ClariFly® are safe when used as directed. These additives require no withdrawal for cattle and can be safely fed until slaughter and to pregnant and lactating cows. Owners of debilitated, aged, breeding, nursing or pregnant horses should consult a veterinarian, however, before using ClariFly. Altosid IGR is not labeled for use in horses or other equines. Additionally, these insecticides are environmentally safe and do not adversely affect dung beetles or other beneficial insects.

Using SWEETLIX fly control products effectively

For fly control to be truly effective, it is vital that all horses and/or cattle on the premises are treated with the proper amounts of additives. Remember: just one female can result in more than 300 MILLION flies in as little as 60 days! Neglecting to treat or under-supplementing even one animal can sabotage your fly control efforts. Carefully read and follow the label instructions and monitor consumption. For maximum benefit, offer SWEETLIX® Fly Control Supplements 3 to 4 weeks prior to the start of fly season and continue until the first killing frost. When introducing these insecticides later in the fly season, remember that they will not kill existing adult flies; other methods of fly control will be needed to mitigate the adult flies.

In summary, don’t wait until a problem appears to implement a fly control program. A good program should be set in place before fly numbers increase. The more flies that are present when control measures are first applied, the longer it will take to bring the population down to a satisfactory level. If you choose to use insecticides, read (and make sure you understand) the directions. Unfortunately, there is no “silver bullet” for the war on flies; however, SWEETLIX fly controls — together with needed mineral/vitamin supplementation, in one convenient package — provide a sound foundation for your fly control program. A successful fly control program utilizing Altosid IGR or ClariFly will also include the removal of all other forms of organic material (e.g., spilled feed, bedding, weeds) in which flies can breed and lay eggs. Minimizing exposure to other organic materials will increase the likelihood that fly larvae will come in contact with and be killed by the larvicide in the manure. Other methods to control adult flies, such as sprays or fly traps, should also be included for a truly effective fly control program.

For more information about SWEETLIX Fly Control Supplements, contact your local dealer or call 1-87SWEETLIX to speak with a SWEETLIX nutritionist.