Field Guide to Flies


Deer Fly/Horsefly field guide
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  • Similar in shape and appearance to the common house fly, horse flies are larger (approximately 1 1/8″ long for adults).
  • Deer flies are ¼” to ½” smaller than horse flies, and usually have patterned wings.
  • They may be black, gray or brown in color.
  • Larvae proliferate in water or moist soil.
  • Winged adults emerge in early summer.
  • Adults live only a few days, and eggs are laid on aquatic plants just above water level.
  • Powerful fliers that can travel many miles from breeding sites to find meals.
  • Female deer and horseflies feed on blood from large mammals (although males do not).


House Fly field guide
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  • Known scientifically as Musca domestica, the most common fly found inside homes.
  • About ¼” long and gray with black stripes on the thorax.
  • No chewing mouthparts, just “sponging” mouthpart for absorbing fluids, such as tears and wound secretions.
  • Breed and produce maggots in moist organic material, such as manure.
  • Found year-round, inside and outside, as long as temperatures are warm.
  • Does not bite.

Stable Fly field guide
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  • Resembles the house fly, but with piercing mouthpart to suck blood.
  • Both males and females attack animals around the flanks and below the knees, causing them to stomp or kick.
  • After feeding, flies retreat to fences or other surfaces to digest their meals.
  • Eggs are laid in moist organic matter, such as wet manure or urine-soaked, fermenting straw, hay or feed.
  • Life cycle completed in 21-25 days during warm weather.

Horn Fly field guide
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  • Small, about 3/16″, and dark gray.
  • Feed by sucking blood from horses and cattle throughout the day, resting continuously on the animal’s shoulders and back.
  • Females lay eggs in fresh cow manure piles.
  • Life cycle completed in 10-14 days.

For information on reducing fly-breeding sites in your region, see “National Defense” in the July 2009 issue of Horse Illustrated.

Further Reading
Insect Control Strategies
Fly Control Resources

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Holly Caccamise has been with Horse Illustrated and Young Rider since 2007, and in August 2019, she took over as head editor. She’s been instrumental in the production of both magazines and helped Horse Illustrated win a 2018 American Horse Publications Media Award in the General Excellence Self-Supported Publication (circulation 15,000 and over) category. Before getting involved in the editorial side of print media, she worked as an award-winning ad copywriter for Thoroughbred Times magazine. Caccamise has her MS in Animal Science from the University of Kentucky, where she studied equine nutrition and exercise physiology, and her Bachelor’s from UCLA in Biology. Caccamise has also worked as a research assistant, horse camp counselor teaching riding and vaulting, and as a top-level show groom in the eventing world, where she continues to compete her horse, Artie, at the lower levels.


  1. Could you give us some options for controlling flies? Isn’t there a plant that repels flies – maybe basil? Will a horse eat basil if you plant it near their stalls? Does putting garlic in their water repel flies from horses?

  2. What about control of Bot Flies? I am finding it really hard to keep them away from the horses. I put the hose over the horses on hotter days, or leave the paddock sprinkler on, so they can get under it, at free will, for relief, but is there a better way. Also, ideas for simple removal of “Bot eggs” would be helpful. 🙂 Thanks!


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