How Bot Fly Larvae Affect Livestock and Farm Income

Bot Fly Removal and Control Practices are Critical for Livestock and Pet Health

How Bot Fly Larvae Affect Livestock and Farm Income

Bot fly larvae are a disruptive, destructive threat to your livestock and not something you or the animals want to deal with during the summer months. The bot fly will lay eggs on or near the animal’s habitat. The eggs will make their way to a suitable spot in your livestock animal, using it as a host while it undergoes changes. Myiasis is the term used to describe a larvae’s transformation from egg to insect, while inside a host animal. In many cases the bot fly larvae will cause damage to the skin or hide of the animal as it erupts at maturity. This will lower the value of the carcass and the hide or pelt. Of course that is just part of the economic threat to your livestock posed by the bot fly larvae.

Each breed of livestock will have a different way of hosting the bot fly larvae. Different animal species have different behaviors when being irritated by the bot fly larvae. The adult bot fly has one purpose in life, which is to lay eggs or bot fly larvae on a host animal.

Small Ruminants and Bot Fly Larvae

Sheep and Goats – In sheep and goats, the main problem with bot fly larvae is from the Oestrus Ovis which is primarily a nasal bot. As mentioned, the Oestrus Ovis Bot fly does not feed on the sheep. It lays larvae right in the nostrils of the animal. These hatched larvae are all ready to eat and annoy the host animal. The sheep tries to run from the annoying thing in its nostrils. The sheep become quite agitated and often go off their feed because they are so bothered by the larvae. Sneezing, difficulty breathing, weight loss, poor condition and even malnutrition can result from a nasal bot fly infestation. If larvae don’t leave the host, they can migrate to the brain. This results in death. The young and the weaker members of the sheep flock are more susceptible to the bot fly larvae infections.


Horse – Gasterophilus intestinalis or the horse bot fly lays eggs on the legs of horses. These look like small white or cream colored rice grains. The eggs are quite sticky and a bot fly “knife” is commonly used to remove the eggs before the horse can ingest the eggs. Once the eggs are laid on the legs, flank or shoulders of the horse, it can reach them when trying to bite an annoying fly or other biting pest. The eggs immediately hatch into bot fly larvae once inside the horse’s digestive tract. The bot fly larvae infestation causes digestive problems. These issues can include, ulceration of the digestive tract, blockage and malnutrition. The mature bot fly larvae are passed out in the manure where they complete the life cycle and hatch out as adult bot flies.

Cattle –  The cattle bot fly, Hypoderma bovis, is also commonly called the heel fly in cattle farming. This species of bot fly attaches its eggs to the heel hair on the cattle’s feet. This annoys the cow and causes it to jump and run wildly, while trying to outrun the annoying insect. Once the eggs are laid, the bot fly larvae migrate by chewing through the skin of the heel area. Their natural route, once inside the host, is to travel up the legs to the throat, then to the back, under the skin. The grub or larvae chew holes for air as they get ready to leave the host. When the larvae exit the cow from the back, they drop to the earth to complete the life cycle. When they hatch, the bot flies begin the life cycle again, laying eggs on the heels of the cattle. This same species of bot fly also attacks deer.


Does the Bot Fly Larvae Live in Pets and Humans Too?

Bot fly infestation can occur in other species of animals besides livestock. Rabbits, cats and dogs can have an occasional run in with the pest. In warbles in rabbits, the bot fly will lay the larvae near the rabbit’s hutch or burrow. As the rabbit brushes by the doorway or the area near the burrow entrance, the larvae attach to the fur. The bot fly larvae then burrow into the skin to feed and allow myiasis to begin. As the larvae feed and grow, a large bump grows under the skin of the rabbit. The bumps are called warbles.

Humans are not exempt from being a host for the bot fly. However, in humans the cases are usually part of a scenario of neglect or unsanitary living conditions. The human genus of bot fly doesn’t directly attack humans. Instead, it lays eggs on a blood sucking insect like a biting fly or mosquito. This transmitter insect then injects the human with the bot fly larvae. This is not the case in livestock and pets. The bot fly will be attracted to the animal,no matter what conditions are present. In other words the cleanest of barns and farm land can still have a problem with the bot fly larvae.

Prevention and Eradication of Destructive Flies

Whether you are goat farming, cattle farming, or sheep farming, controlling pests that cause economic loss in the herd is of top importance. Horn flies, face flies, and bot flies all cause loss to the farming industry and make the livestock suffer. Horses have been known to hurt themselves trying to avoid the flies. Sheep may likely stop grazing and rub their noses on the ground because of the irritation. Goats will often hide in a dark place when bot flies are present, in order to avoid the pest. All of these evasive actions interrupt the life of the animal and cause economic loss to the farmer.

Horn flies in cattle herds stay on the cow except when they are laying eggs in the manure. They are not very strong fliers and tend to hover close to the cow. Unlike the bot fly, the horn fly does bite and eat blood from the host. The face fly feeds on eye secretions. This pest can spread germs and infections such as pink eye in horses and cattle.

Insecticide use can help control fly population and infestation. The risk and hazards of using insecticide should be weighed by each particular farmer. Organophosphates should be avoided as they can do much more harm to the animal and the environment than the bot fly larvae. Permethrin insecticides or sulphate chemical control is used for cattle operations. The caution noted is to use one or the other, but not both at the same time. Using both at the same time can lead to resistance of the pest to the treatments. Cattle are sometimes fed a fly control substance called an Insect Growth Regulator to control fly populations. Controlling flies in cattle herds increases growth rate for calves and increased milk production.

In the case of screwworm flies, which were prevalent in the southwest part of the United States, releasing sterile male flies helped to eradicate the screwworm fly. But in areas of Mexico which did not participate in the program, the fly is still doing considerable damage to livestock. However, there is no program like this for the bot fly.

Have you had problems with bot fly larvae in your livestock or pets? Please tell us about your experience in the comments section below.

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