Fly Predators for the Horse Farm

Those of us that have horses or even other farm animals have probably accepted the fact that flies just come with the territory.  They’re really annoying, but what can you do? Sure, we have all sorts of ways to combat the pesky insects for a while, but it seems like no matter what we do, they just keep coming back.  A few weeks ago, they seemed to come out of nowhere at my place.  One day there were none and the next, there were like a jillion of them buzzing around my house and my horses.


flies on horse


The main reason flies tend to congregate around horses and farms is manure.  Flies are natural decomposers of rotting organic matter such as manure and dead plants and animals. So of course, if you have lots of manure around, you’ll get an abundance of flies.

There is no one method which will eliminate them all, but a few years ago, I learned about a unique and reportedly effective way to get the upper hand on the fly population on your farm.  They’re called fly predators (trade name used by Spalding)–maybe you’ve heard of them?  I’m excited to say that I will be trying them out for the first time this year!

The term fly predators actually consists of not one, but several different insect species including: Muscidifurax raptorellus, Spalangia cameroni or Spalangia endius, Muscidifurax zaraptor, and sometimes insignificant quantities of other fly parasitoid species.  These insects are natural predators of the common house fly, horn fly, biting stable fly and the lesser house fly and feed on their larvae.

What I love about the fly predators is that they are a completely natural means of controlling the fly population.  There are no chemicals or sprays, and there is nothing toxic involved.

Another great thing about these tiny fly killers is that they are completely harmless to humans and animals. They don’t bite or sting and they often go unnoticed because of their tiny size.  They will mainly hang out near manure piles in the pasture, where flies lay their eggs.

According to Spalding, pest flies reproduce nine times faster than the fly predators do, so it’s important to add supplemental Fly Predators every three to four weeks during the warmer months to keep the fly population under control.  Spalding works with customers to create a treatment schedule specific to their farm (depending on number of animals and size of farm) and customers will receive shipments of the fly predators on that set schedule.

I received my first shipment of fly predators last week.  The directions on the bag say that after a dozen or more of the fly predator larvae have hatched (in the bag), they are ready to go, so I ‘released’ the fly predators this past weekend.  It was actually kind of a fun experience.  (if you take pleasure in knowing that the flies will soon DIE!!!)


fly predators2


You sprinkle them around moist manure or other rotting organic matter.  Covering them slightly is also recommended.  I sprinkled them around 10 or 15 individual manure piles in the pasture, on my big manure pile behind the barn, and then I left a few in the bag and placed them in the breezeway of the barn (per the instructions).  It should take about 30 days to see results.  I will be sure to report how they work as we go along.

I would also like to mention that manure management is very important and I do this as well.   Picking up manure from stalls, pens, and pastures will not only help control flies, but also other equine parasites.

And of course, fly sprays are usually helpful to use on the horses, themselves.  I like to make my own non-toxic fly sprays, using recipes from this post.  But we all know that sprays can only last for so long and they do nothing to curb the fly population on your horse farm. . .

If you’re interested in learning more about fly predators or would like to order fly predators for your farm, be sure to click here.






Hi! My name is Casie Bazay. I'm a mom, a freelance writer, and a certified equine acupressure practitioner.

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2 Responses

  1. Susan says:

    I tried the fly predators a few years back. I have a lot of horses here so the monthly order was fairly expensive. I followed the directions to the “t”. We did not notice any reduction in fly population. If they did do their job, maybe it was on certain flies but not others. They don’t kill them all!

    • Casie says:

      Hmmm-that’s too bad, Susan. I’ve heard lots of people report that they did make quite a difference. Did you order from Spalding? Also, are there cattle or other livestock nearby? I know that can make a big difference.

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