Get Tough on Flies: Straight Talk on Protecting Your Horse

It’s a fact of life. If you have horses, you have manure. If you have manure, you’re most likely going to have flies.  

Flies not only annoy and stress animals, but they can also carry contagious diseases from one horse to another. Even non-biting flies can be a source of irritation and annoyance. Fortunately, there’s something you can do about eliminating many of those pesky insects. 

Good “housekeeping” is the most effective way to get a handle on your fly population. You can use all of the newest products out there, but if you don’t remove the manure, garbage and overgrown weeds or grass in your barn area, it will be impossible to control the fly problem. 

Fly Facts

A female adult housefly lays up to 500 eggs in her lifetime, but in a normal environment only 2 to 4 percent of the fly eggs laid make it to adulthood.

A house fly goes from an egg laid in manure to an actual fly in no less than eight days. The female lays her eggs on or close to rotting organic matter – manure mostly, but also rotting vegetation. These eggs hatch into larvae, which feed and pupate. Adult flies emerge from the pupae; there are no “baby” flies; when each fly emerges, it is already an adult. Those adult flies live an average of 21 days, but can live anywhere from a week or two in hot weather, or months in cool weather.

There are simple things you can do to dramatically reduce the amount of flies you have just by making it hard for them to reproduce. Simply removing trash and manure at least once a week will make an enormous difference.

Flies are quite sensitive to moisture, which is why manure management is so important. If the larvae (maggot) is in an environment that is drier than 40% or wetter than 60% moisture, the pupae doesn’t form properly and that fly never completes its development. If you can’t have manure hauled away weekly, concentrate it into one big pile because the middle of the pile will get very hot as it starts decomposing, too hot to support fly reproduction. If you live in a dry environment, spread the manure out so that it dries within five days (the soonest flies get to the pupal state). This means fewer flies developing in that manure will make it to adulthood.

Have a Plan 

To win the fly control battle, horse owners must have a multipronged plan. This includes: 

• Conscientious manure management
• Fly sprays and/or topicals for the horses themselves
• Premise sprays and/or traps to reduce fly population around the barn
• Feed-thru fly control to break the fly life cycle 

Sweat-resistant fly control formulas and topical products have become popular because they stay on the horse and keep working even through sweat and rain. Be sure to actually read the labels on all repellent and insect control products. You must follow label directions carefully to get the best results. Frequently, when you don’t see the desired results, it’s because you didn’t apply enough of the product or didn’t apply it correctly. 

Feed-thru fly control products are added to the horse’s feed and must be used daily for continued effectiveness. The product works by killing the larvae in the horse's manure, which helps prevent the development of stable and house flies in manure. Because this doesn't affect adult flies, additional measures are needed for overall fly management. 

Additional fly control measures include native fly parasites and, if you have stabled horses, an automatic fly/insect spray system in the barn. Native fly parasites can be purchased through companies that sell them specifically for fly control. Typically, these tiny parasites are scattered in the close vicinity of moist manure. Timing is important, as they should be released shortly before flies emerge and at intervals throughout fly season. Fly parasites are actually minute wasps that kill fly pupae by feeding on it and depositing their own eggs into live pupae, thus preventing the development of adult flies. 

Barn spray systems can also be highly effective, but consistent good housekeeping is required as well. Proper sanitation and manure removal cannot be ignored if you want to win the war on flies.