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Field Guide to Flies

Know your enemy. Read up on the pests that might be bugging your horse this summer.

By Holly Werner | July 2009 Exclusive

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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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Field Guide to Flies

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Reader Comments

Galadriel    Lothlorien, ME

8/3/2013 11:48:17 PM

Excellent article. And very timely.

Horsegirl    Horsetown, GA

2/4/2012 7:25:52 PM

thanks for the info

Nan    Longford, Australia, AL

3/20/2010 5:28:58 PM

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!

Linda    Ithaca, NY

6/4/2009 6:53:56 AM

Thought it was very informative, thank you.

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