What The Muck Is That?

Each week we will investigate one equestrian conundrum in “What the muck is that?”  This week … flies that bite.

Horse Bots

Bee-like fly 1/2 to 3/4 inch in length.

The eggs are firmly glued to the hairs of the forelegs, belly, flanks, shoulders and other parts of the body of the horse.

The eggs are ready to hatch 7 to 10 days after oviposition, and will hatch only if the horse licks or bites the area where they have been glued.

The larvae fully mature inside the horse and begin the process anew when passed through droppings.

Can cause mild to severe damage to the soft tissues of the mouth, tongue and all gastrointestinal organs.

  1. For external insecticide treatment, a warm water wash (110 -120° F) should be rubbed or sponged on areas infested with eggs.
  2. Eggs can be removed with pumice stones, bot knives or pinched fingers.
  3. For internal treatment of horse bots, consult a veterinarian.


Horse Flies

Daytime feeders, vicious biters, and strong fliers.

The eggs are deposited on objects over water or moist areas.

Eggs hatch in 5 to 7 days and the larvae fall to the surface of the water or moist areas where they begin to feed on organic matter.

When the larvae are ready to pupate, they move into drier soil, usually an inch or two below the surface. The pupal stage lasts 2 to 3 weeks, after which the adults emerge.

The life cycle varies considerably within the species, requiring anywhere from 70 days to 2 years.

Attacks often account for lowered weight gains and reduction in condition.

Known mechanical transmitters of diseases such as anthrax, tularemia, anaplasmosis, and equine infectious anemia (EIA).

  1. No treatment for larvae exists, though mowing tall grass and weeds is highly recommended.
  2. Apply external fly repellant to discourage adult flies.
  3. Fly masks, leg wraps, and sheets provide some relief.


Stable Flies

Bayonet-like mouthparts of the stable fly differentiate it from the house fly.

Vicious biters and strong fliers that range many miles from the breeding sites.

Stable flies breed in soggy hay, grain or feed, piles of moist weed or grass cuttings, and in manure mixed with hay.

Eggs hatch in 2 to 5 days and mature in 14 to 26 days.

Average life cycle is 28 days.

Adult flies are capable of flying more than 90 miles from their breeding site.

Mechanical transmitters of anthrax, equine infectious anemia (swamp fever), anaplasmosis, and Habronema stomach worms.

  1. Remove sources of stagnant water and mow grass and weeds.
  2. Hang insect traps.
  3. Apply external fly repellant to discourage adult flies.
  4. Fly masks, leg wraps, and sheets provide some relief.


Sand Flies, Biting Midges, No-See-Ums

Associated with wet habitats.

Life cycles and habits of midges affecting livestock are poorly known.

Horses may lose hair in the infected areas because of fly feeding.

  1. No effective control measures are available for these flies.
  2. “Insecticides, larvicides and repellents are either useless or very limited in their success in fighting No-See-Ums.  Even DEET offers only limited No-See-Ums protection.” (SOURCE)
  3. CO2 traps have limited success, but are cost restrictive.


Black Flies

Small, dark, stout-bodied flies with a hump-backed appearance, strong fliers.

Blood feed during daylight hours.

Eggs deposited on logs, rocks or solid surfaces in swiftly flowing streams.

Hovers around the eyes, ears, and nostrils of animals.

Large numbers of bites may cause weakness from blood loss, anaphylactic shock, or death.

  1. Animals should be kept out of river basins.
  2. Fly masks with ear and nostril covers may provide minor relief.


Horn Flies

Found only near cattle as larvae do not develop in horse manure.

Migrate extensively after reaching adult stage.

Persistent blood feeders that cause skin lesions.

  1. Fly spray, fly masks, leg wraps and sheets are all effective.

You might have noticed I didn’t discuss poo management in the fight against flies; next week on “What the muck is that?” we will discuss the wonderful world of manure.

Go Riding!



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