Dairy operators face a number of management problems during the production season. One of these problems is the control of insect pests.

Insect pests generally fall into two groups: insects that feed on the animal and insects associated with conditions around the dairy.

Insects that feed on animals
Pests such as flies, lice and mites may occur on dairy animals at different times throughout the year. Flies that may be found on or around dairy animals include horn flies, stable flies, and horse/deer flies. These flies are blood feeders and occur during the warmer parts of the year. Conversely, lice are found during the cooler months of the year but are also blood feeders. Mites on dairy animals include mange mites, which burrow through the skin and occur in hair follicles or under scabs that form as a result of feeding. Mange mites cause a great deal of irritation to the host animal, and this irritation may result in lowered milk production or reduced growth in replacement heifers.

Horn flies
The horn fly is a small blood-feeding fly (both males and females are blood feeders) that overwinters in pastures as a pupa. Adult flies emerge when springtime temperatures reach the high 60s or low 70s, and they immediately seek a host and begin feeding. Horn flies potentially can be present on the animal from this time until the cooler temperatures of fall and winter. After mating, females leave the animal for short periods of time to lay eggs at edges of fresh manure pats.

In summer temperatures, eggs can hatch in 24 hours. Larvae will feed within the aging manure for four to six days before crawling a short distance to drier areas around the manure pat to pupate. Adult emergence will occur in about three days.


A cycle from egg to adult takes eight to 10 days. There can be as many as 10 generations per year; however, there are two peak population points during the year. One will occur in late spring to early summer followed by another in early fall.

Stable flies
This fly is a little larger than the horn fly and is also a blood feeder (both males and females feed on blood), but it only visits a host animal when ready to feed. When not feeding, stable flies can be found resting on barn walls, fence posts, tree limbs or similar sites. If the fly is viewed from the side, the tubular piercing/sucking mouthpart called the proboscis is very prominent. This feature distinguishes the stable fly from both the horn and housefly.

The stable fly will breed in manure; however, higher numbers of flies are produced in a combination of manure and hay or other decaying organic matter that produces a fermentation smell. The cycle from egg to adult is comparable to that of the horn fly at 85ºF.

Horse flies/deer flies
Horse flies are fairly large, heavy-bodied flies with the larger species being about 1-inch long; most deer flies are less than 0.5-inch long. Females are found on or around cattle only when they are in search of a blood meal. Males are nectar feeders.

Depending on species, larvae are usually found buried in mud along the sides of streams, ponds, roadside ditches, salt marshes or the overflow areas associated with rice fields. A few species may develop in pasture soils or in leaf litter under trees. The life cycle of these flies is poorly studied, but in most cases, it appears that there are one to three generations per year. Adults are long-lived flies and some will be present throughout the summer.

These flies do not pierce the skin to obtain blood but rather use the cutting action of the mouthparts to create a wound. As the blood flows from the wound, it is absorbed by a section of the mouthparts that is sponge-like in nature. Creation of the wound is highly irritating to the host animal. Because these flies are highly mobile and spend little time actually on the animal, it is very difficult, if not impossible, to control these flies.

Sucking lice
Louse infestations occur during the winter months, and this added stress can result in poor growth in replacement calves or reduced milk production in adult animals. Very low louse numbers may be present on animals during the summer months. Then reproduction increases as the weather cools in the fall, and by spring of the following year, louse numbers can be very high in uncontrolled situations.

Adult males and females as well as lice in all life stages are found on the animal. Females attach their barrel-shaped eggs (nits) to the hair shafts, and it may take 10 to 14 days for eggs to hatch. Nymphs begin to feed as soon as they hatch and will feed frequently. Infestations may be found on the head, neck and withers or along the inner surfaces of the legs.

Heel flies or cattle grubs
Heel flies are not as common as they were prior to the mid-1960s, but they still occur occasionally. Eggs are deposited on leg hairs of the host animal in the spring. The eggs hatch within two to four days, and the young larvae or cattle grubs bore into the body and migrate through the connective tissue of the host animal. The migratory process eventually ends with the formation of a warble on the back of the animal the following spring.

Approximately half-way through this process, the grubs will accumulate in the esophageal area and may remain in this area for 6 to 10 weeks. This time frame may include parts of October, November, December and early January. It is important to apply controls before they accumulate in the connective tissue of the esophagus. If large numbers are killed in the esophagus, the byproducts of decay may compromise health of the host animal. Therefore, treatment needs to take place before October 1.

Mange mites
Two species of mange mites may occur on dairy animals, particularly in animals that are in confined situations either as adults or calves. Chorioptic mange is probably the most common form of mange in cows. The first lesions may be found in the tail region and then spread to other parts of the body. Scabies infestations may also occur on dairy animals, but they are less common than chorioptic mange. The first lesions are usually on the head and neck and spread from this area to other parts of the body.

In the case of scabies, symptoms usually appear as encrusted areas with thickening of the skin, which then may lead to small folds of skin on the neck. To relieve itching caused by the mites, the animal will rub against objects and will lose some hair as a result.

Chorioptic mange will cause the skin to appear scaly with a crust formation and a thickening of the skin. In some cases, the skin may appear moist. If you suspect a mange infestation, consult with your veterinarian for diagnosis and treatment.

Insects associated with the dairy
Insects in this group do not feed on the animal but are attracted to the area by manure, spilled feed, moisture or harborage. A number of insects may fall into this category; however, houseflies and cockroaches are the most problematic.

Adult houseflies have sponging- type mouthparts. They feed by regurgitating small amounts of digestive enzymes onto the surface of the food source and then sponging up the resulting predigested liquid. Houseflies feed on a wide variety of foods, some of which may be in some stage of decay. Animal excrement can serve as a food source or as a breeding site. These flies are very prolific, and there can be eight to 10 generations per year. Females deposit eggs on the surface of a wide range of decaying organic material such as manure, fermenting feed, silage waste areas, lagoon overflow areas, decaying grass or similar sites.

Eggs may hatch in less than a day under optimum conditions. After hatching, larvae will feed for three to seven days and then seek out slightly dried areas for pupation. The pupal period will last three to four days. Newly emerged adults will feed and mate, and females lay eggs within two to four days after emergence from the pupal case. When not feeding, houseflies rest on barn walls, ceilings, stall supports, fences, light wires or various plants.

Although there are several different species of cockroaches, only three are considered pests on dairies: the American, smoky brown and German cockroaches. American cockroaches are about 1.5 inches long and are reddish brown in color, while the smoky brown is 1 to 1.25 inches long and is dark brown to black. After mating, females develop egg cases that remain attached to the body for about 24 hours. At this time, the egg case is indiscriminately dropped at some point or is glued to a surface.

Egg cases contain 14 to 16 eggs for the American and 24 eggs for the smoky brown. Females of both species will produce about 20 egg cases during the warmer months of the year.

The German cockroach is much smaller than the other two species, measuring only about 0.5 to 0.625-inch long. It is light brown in color with two dark stripes on the cap (pronotum) above the head. German cockroach females retain the egg case until the eggs are close to hatching. At this point the egg case is attached to a surface in areas frequented by the female; each female produces four to eight egg cases, with each case containing 30 to 48 eggs.

In some situations, German cockroaches may be found in natural settings, but most are found in buildings. The American and smoky brown can be found outside as well as within buildings. Once inside, the insects prefer warm, moist areas with an available food supply and may be found around pipes, hot water tanks or sewage systems. Smoky browns can be found in slightly drier areas than either the American or German.

Cockroaches will forage for food during the night and feed on a wide variety of foods including animal excrement, milk, milk byproducts, dead insects, fresh or dried blood, or any food that could be used for human consumption. Depending on feeding sequence, these insects might move disease organisms from one food source to the next.

These arthropods may live around dairy barns, and although spiders do not cause any problems with livestock, their presence along with associated webbing may be perceived as unsanitary during inspections. Although one might argue that spiders are a form of biological control given the fact that they feed on insects and flies, their webs collect dust and insect body parts, which could serve as sources of milk contamination.

Two spiders that might be found around barns are the house spider and the long-bodied cellar spider. The house spider is small, measuring only 3 to 5 millimeters in length. As described in How to Know the Spiders, 3rd edition, by B.J. Kaston, “This extremely common spider is found most often in barns and houses where it makes its webs in the corners of rooms and in the angles of windows.” The front part of the body is yellowish brown while the abdomen is off-white to brown with distinctive gray striping.

Long-bodied cellar spiders have an extremely long abdomen when compared to the rest of the body. They are pale yellow except for a gray area behind the eyes. Females are almost 1 centimeter in length. These spiders spin large, irregular webs.

Mosquitoes belong to the same group of insects as the house, horn, stable and horse flies, but their bodies are not as robust as these other flies. Female mosquitoes are blood feeders and some will feed primarily on birds, while other species feed on many small or large mammals. Males are nectar feeders.

Not only are mosquito bites irritating but they can also transmit disease during the biting process. Mosquitoes are capable of transmitting a number of diseases; however, the encephalitic viruses are the most prominent disease group that may be carried by mosquitoes in the United States. These viruses are found in nature in different bird species and are carried from birds to other birds, humans and horses by several species of mosquitoes.

Female mosquitoes lay their eggs on or over a body of standing water. Possible water sources could be birdbaths, wading pools, pet watering containers, aquatic gardens, used tires, improperly maintained swimming pools, runoff from sewage lagoons, runoff from silage pits, temporary pooled water in tractor ruts and any other area that might hold water for eight to 10 days.

Eggs hatch in 24 to 48 hours, and larvae will feed for a period of five to seven days before pupating. The pupal period will last for about two days. After this period adult mosquitoes emerge and the females immediately seek out a suitable host in order to obtain a blood meal.

On-animal insect control
Controls for on-animal insects are largely based on the use of an insecticide. Depending on the active ingredient and how it is formulated, these materials may be used as pour-ons, sprays, backrubbers, ear tags or feed additives.

Premise insect control
Pests such as houseflies, cockroaches and spiders are attracted to dairies because of available food, water and shelter. Although chemical controls seem like the best first line of defense against insect pests around the dairy, nonchemical methods such as sanitation and physical methods are actually the most important components of managing dairy- related pests.

Time is an important element when operating a dairy, and some of these methods, especially sanitation, can be time-consuming. However, this is not a good reason to overlook these basic premises of pest control. Time spent getting rid of feeding and breeding sites will result in fewer flies and cockroaches, which will make chemical controls more successful if they are needed.

Manure management
There are a number of methods to remove manure from barns. It may be washed into lagoons (the most efficient method) using some type of automated system, or it may be scraped up and spread onto pastures or stacked to be spread at a later date. During the washing process, some manure may be caught on posts, building supports, in corners or behind feeding bunkers or troughs. If automated systems are used, some touch-up may be needed to ensure complete removal.

Spreading manure in a field as thinly as possible allows the manure to dry. The drying process makes it unattractive to flies as a feeding or breeding site. Stacked manure should be kept below 30 percent moisture, and the drier the better. Manure at or below 30 percent is not attractive as a breeding site for flies.

Do not overlook manure in calf pens. Manure mixed with bedding can provide breeding areas for houseflies and stable flies. During the fly breeding season, clean these areas as frequently as possible.

Excess feed removal
Dairy feeds often contain sweet materials such as molasses or brewers yeasts and these materials are very attractive to flies and cockroaches. Small amounts that may accumulate under feeding areas or in corners can provide food for flies or cockroaches. Cleaning these areas periodically will help reduce available food materials.

Silage that is spilled around silos or trench bunkers also provides adult-fly food sources as well as a breeding site for flies. Keeping spillage to a minimum and providing good drainage around trenches will help eliminate available feeding and breeding sites.

Preventing a pest from gaining access to an area is a reliable pest control technique. This concept may not work well on a dairy farm given the constant movement of cows and personnel in and out of barns and milking parlors. However, it may prove useful in specific areas such as milk rooms. Make sure doors and windows fit well, and if windows are open, make sure screens are in place and in good shape.

Cockroaches may move along water pipes within wall voids and then out into room spaces at points where the pipes enter the room. Caulking around pipe openings will prevent the roaches from moving into the room. Caulking may also be used around window and doorframes or at points where other service lines enter the room.

Insect light traps
A number of insects, including houseflies, are attracted to the ultraviolet (UV) light source used in light traps (also called black light traps). Historically, traps were fitted with the lights and an electrical grid. To reach the light source, insects had to fly through the grid, where they received an electrical shock. The electrocution process often caused smaller insects to explode, sending insect body parts into the surrounding air space. This led to contamination concerns, especially in food processing areas.

Many traps today are still fitted with the UV lights but most have replaced the electrical grid with a glue board. This type of light trap is ideal for use in milk rooms. If possible, place traps five feet above the floor and do not allow them to be visible from the outside. Clean the trap monthly during fly season and replace the glue boards. Replace bulbs yearly because UV bulbs may lose their attractiveness to flies long before they burn out.

Baited traps
Cockroaches are attracted to a number of food odors, so highly volatile fermenting odors can be used in traps for these insects. One example is a homemade jar trap that can be used to survey an area for cockroach populations, or if a small area is involved, it might be considered a control option. To use this method, take a quart- or gallon-size jar and coat the inner surface of the jar neck with a film of petroleum jelly. Next, place a small piece of bread in the bottom of the jar and moisten it with 15 to 20 milliliters of beer, fermenting fruit juice or place a small piece of overripe banana in the bottom. Place jars under sinks next to the wall, under or around bathroom fixtures, against walls or around hot water tanks. The jars could be put in place after cleanup at night and checked the following morning. Destroy any trapped cockroaches.

Light management
Spiders are attracted to dairy structures because of the presence of insects they eat. Insects other than flies and cockroaches are attracted to lighting that may be used around the structures at night. This may draw more spiders. If possible, reduce the amount of lighting used at night or use lighting less attractive to insects. Lighting that provides a yellow spectrum is less attractive than bright white or slightly blue light.

Physical removal
Vacuuming has been used successfully for pest control and would be a good option for removing spiderwebs and spiders from dairy facilities. HEPA filters are also available for these. A vacuum can also be used to clean up feed that might have worked its way into hard-to-reach areas around the barn. Vacuuming performed periodically throughout the year is much better than a “crash cleaning” just prior to your annual inspection.

Water management
The presence of water determines if you will have mosquitoes on your dairy. Anything that can be done to eliminate standing water will help reduce mosquitoes. For example, old tires used to hold down coverings on silage pits provide excellent mosquito breeding sites. Drilling holes or making slits in the tires allows collected water to drain out, which prevents the area from serving as a mosquito breeding ground. If mosquitoes are problems in and around the barn, sprays used to control houseflies will also control adult mosquitoes.

Insecticide applications
Following cleanup, insecticide applications can be applied to various surfaces if needed. It is much easier for insects and spiders to absorb a residual dose of insecticide from a clean surface than from one covered with dust or oily film. When applying insecticides in the milking facility, treat each area uniquely. The facility may contain a number of different areas, including a congregating area for cows prior to milking, the milking parlor, the milk room and possibly a post-milking feeding area.

Prior to milking, the cows congregate in an area adjacent to the milking parlor, and the accumulation of manure in this area may contribute to housefly populations in other sections. Prompt removal of manure from this area will help reduce housefly numbers. After cleaning, residual insecticides can be applied to fly resting surfaces in this area.

From the congregating area the cows move into the milking parlor. Once the milkers are attached, the milk is in a contained system and is not exposed to outside contamination sources. When using residual insecticides in this area make sure that teat cups, other milking equipment and feeding stations are not contaminated with residual sprays.

The milk room is considered a food processing area, and available products are limited. Rely on sanitation and physical methods as the primary means of pest control in this area. If it becomes necessary to use any insecticide in the milk room make sure that cooling equipment and bulk tanks are protected from possible contamination. PD

References omitted but are available upon request at editor@progressivedairy.com

—Excerpts from Mississippi State University Extension website

James H. Jarratt, Extension Entomologist, Retired; Blake Layton, Extension Entomologist; Mississippi State University; and Jerome Goddard, Medical Entomologist, Mississippi Department of Health