Bug v. Bug — And You Win

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When you have 100 horses on your farm, flies can be a big problem. But when Tim and Brenda Johnson welcomed a 400-person crowd to an open house last year at their Excalibur Breeding Center in Garrison, Minnesota, flies were most notable for their absence.

“We had many people say, ‘You don’t have any flies,’” recalls Tim Johnson. “And I said, ‘No, we don’t.’”

How does Johnson boast a fly-free environment despite the farm’s huge herd of horses and the notoriously bug-ridden northern Minnesota locale? He chalks it up to a little bug that’s proved more partner than pest. Commonly known as fly parasites (or by the trade name Fly Predators®), these beneficial insects are members of the wasp family. But they have no stinger, are approximately the size of a gnat and have no interest in harassing humans or animals. Their only goal in life is to seek out and destroy fly pupae, and reproduce so the next generation can follow in the family trade.

The Johnsons learned about the insects from a customer. Fed up with sprays and other fly-control paraphernalia, the couple gave the bugs a try. That was three fly seasons ago, and the Johnsons are more sold than ever on this all-natural method of keeping pest flies at bay.

What They Do

Fly parasites work by laying their eggs in pest-fly pupae (the cocoon), effectively killing the immature fly before it ever hatches, explains Tom Spalding, proprietor of Spalding Laboratories, which sells Fly Predators. (Since fly parasites work on larvae, not adult flies, you won’t see immediate results. A difference is typically evident about 30 days after starting the program.)

Fly parasites combat most pest fly species, including house, horn, face and stable flies. Spalding’s website reports on three studies proving the efficacy of these insects. In one, fly parasite use suppressed a house fly population within 30 days. In another, populations of house and stable flies were eliminated at a poultry house after 98 days. In the third, fly parasites led to a 93 percent reduction in common biting stable flies.

Johnson, who uses Spalding’s Fly Predators, has personally seen a definite decline of barn and house flies at his farm. He says the good bugs aren’t effective against his area’s deer and horse flies (species which, according to Spalding, breed in water rather than on land). But since those species typically invade for a shorter portion of the year, this deficiency doesn’t worry him.

By the Numbers

An effective fly-parasite program requires an adequate number of fly parasites, particularly since pest flies reproduce faster than fly parasites. To prevent the good guys from being quickly overwhelmed, most suppliers recommend monthly shipments of fly parasites for several reasons. According to the Source Biological Fly Control website, fly parasites are able to complete a generation every three to four weeks, giving rise to an increase in their own population as they reduce the number of flies. However, pest flies have a distinct advantage in actual numbers produced: A single fly will lay up to 900 eggs, but a single parasite will attack less than 50 fly pupae.

Second, the life cycle of a fly is also much shorter than that of the parasite, and this contributes to the pest’s advantage in reproductive capability.

Third, the size and strength of the fly are important advantages that enable it to travel greater distances, and to some extent, resist the effects of pesticides more effectively.

Johnson learned the importance of numbers the first year he tried fly parasites. He told the supplier how many horses the farm typically hosts—but forgot to take into account breeding season, when the facility is home to more than 100 horses. So he didn’t get as significant a control impact as he’d hoped. Since upping the quantity of fly parasites he receives, Johnson has been more than satisfied and now advises others to “overshoot the minimum you think you’ll need.”

That minimum recommendation varies depending on multiple factors, including number of horses, facility size, extent of your current fly problem and even your neighbors. For his Fly Predators, Spalding suggests shipments of about 1,000 insects per horse per month. While Johnson hasn’t kept track of the total number of fly parasites he uses each season, Spalding’s records indicate that the farm receives about 600,000 Fly Predators in a normal year.

While these figures may sound high, Johnson says that you just don’t notice the fly parasites. The insects don’t travel far from manure piles and other sites where decomposing organic matter attract pest flies to feast and reproduce. And they typically hover less than a foot above these locations. Combined with their small size, this tends to keep fly parasites out of sight and out of mind.

The Cost of Protection

When you talk about buying thousands of something, it’s natural to assume there’s a high price tag involved. But proponents say the cost is a benefit. According to Johnson, the price of fly parasites “is minimal compared to what we spent on sprays, fly bags, fly tape and so on.”

Exact prices, of course, vary by supplier, number of insects and frequency of shipments. But you can estimate anywhere from $15 to $30 for an order of 10,000 to 15,000 fly parasites.

Most suppliers recommend releasing your first batch of fly parasites soon after the last frost and, ideally, before any pest flies are zooming around the barn. Suppliers generally recommend continuing with regular monthly or semi-monthly shipments throughout fly season, until the first frost of fall.

Spalding notes that the cost for Fly Predators runs about $4 per horse per month for less than 25 horses, with the cost falling to about $2 per horse per month if your farm is home to more than 25 horses. Based on these costs, a farm with 30 horses that received shipments over six months would pay approximately $360 for the year.

Once you have a good fly-parasite population established, though, you may find that fewer orders or lesser quantities will still get the job done. While this isn’t always the case, Spalding recalls one long-term customer who started 20 years ago with 100 horses. “Now they have 200 head and still use the same number of Fly Predators,” he says.

Putting Them to Work

Ease of use is another benefit to fly parasites. All you do is open the delivery bag and sprinkle the fly parasites on the largest concentrations of manure and other sites where pest flies breed. Since fly parasites don’t travel far, you’ll want to release them in each location where flies may be breeding.

If you continue using pesticides, especially those geared toward fly control, keep them away from the areas where your fly parasites live, as the chemicals will destroy the beneficial bugs along with the pesky ones. Similarly, if you need to apply bug repellent to your horse, do it away from your fly parasites.

You also want to keep your fly parasites away from ants and birds, which see your fly-control partners—or the pupae they’re in—as a tasty snack. For instance, Johnson releases fly parasites at many locations around the farm, but not at the barns, where he keeps chickens to help manage the local wood ticks. However, Spalding says you’re probably safe to simply hang the delivery bag of fly parasites above the chickens’ reach.

It Takes a Neighborhood

There’s one more key to an effective fly-parasite program: your neighbors. Since pest flies can travel about a quarter-mile (while fly parasites rarely stray more than 300 feet from where they’re released), if your neighbors don’t have a handle on their fly population, it won’t take long for their problem to become yours.

Johnson acknowledges that one reason he’s seen such success at his farm is that there are few other livestock owners in his area. If you’re not so lucky, talk with your neighbors about creating a community-wide fly-control plan. For instance, Spalding notes that some of its customers have created neighborhood groups that purchase quantities sufficient to cover all their properties.

Just One Tool

Of course, even the most effective fly-parasite program, with complete neighborly cooperation, probably won’t destroy all fly pupae (although Spalding claims 95 percent effectiveness) and won’t impact existing adult flies or pests that don’t breed in manure. So fly parasites should still be just one part of a multi-faceted plan that includes smart manure management, fly traps, other natural allies (such as birds, bats and even some fish) and possibly selective use of sprays. Put it all together, and you may just win the battle of the bugs this year.