The Most Fascinating Biology of Fly Predators

Fly Predators are what biologists call parasitoids. That is, they are classified somewhere between predators and parasites. Like other parasites, Fly Predators are much smaller than their pest fly host. However, the effect the Fly Predators have on the pest fly’s population is exactly like a predator in that the Fly Predators kill the immature pest flies.

Andy Collman, Cloud Cap Farm Boring, OR.

“We’ve noticed how effective Fly Predators can be. They’re now part of our fly control program which also includes keeping things as clean as possible.”

Andy Collman, Cloud Cap Farm Boring, OR.

Technically Fly Predators are tiny Hymenopteran insects of the Pteromalidae family, a family that contains many of the world's beneficial insects. These are pupal parasitoids as they attack the pest fly’s pupa stage (the cocoon that houses the pest fly during its metamorphosis from larva to full-sized adult). Fly Predators are sometimes referred to as parasitic wasps, but unlike other Hymenopteran insects, such as bees, wasps and ants, Fly Predators are completely biteless and stingless.

Currently the mixture of species marketed under the trade name Fly Predators include: Spalangia cameroni, Spalangia endius, Muscidifurax zaraptor, Muscidifurax raptorellus in varying ratios and may at times include insignificant quantities of other fly parasitoid species. This balanced mix of multiple strains and guaranteed yield from the most advanced quality control techniques means you can always count on the best results with Spalding Fly Predators.

Fly Predators never become a pest themselves. Being passive insects, they do not crawl all over you when being handled, nor will they migrate into living quarters as pest flies do. Since Fly Predators live their entire life cycle on or near the surface of manure and other decaying organic matter, and because they are so small in size, they go virtually unnoticed.Fly Predators never become a pest themselves. Being passive insects, they do not crawl all over you when being handled, nor will they migrate into living quarters as pest flies do. Since Fly Predators live their entire life cycle on or near the surface of manure and other decaying organic matter, and because they are so small in size, they go virtually unnoticed.

When they are released near fly breeding sites, the female Fly Predator searches through the area seeking out the fly’s pupa. After locating one, she drills a hole in the pupal case, inserts her ovipositor, and deposits from one to a dozen eggs inside. After her eggs are deposited, she obtains nourishment by ingesting the fluids of the developing pest fly. The female Fly Predator then moves on and repeats the process until all her eggs have been deposited.

The Fly Predator's eggs that were deposited inside the pest fly pupa will develop into Fly Predators. Immediately upon emergence the Fly Predators mate and start the cycle all over again.The life span of the female Fly Predator ranges from as little as two weeks to as long as one month. She will live just long enough to deposit all of her 50 to 100 eggs. When the pest fly’s population is under control and only a few pest fly hosts are available, the female Fly Predator has the ability to reabsorb her eggs as a source of nourishment and thus is able to live up to a month while searching for pest fly pupae.The life span of the female Fly Predator ranges from as little as two weeks to as long as one month. She will live just long enough to deposit all of her 50 to 100 eggs. When the pest fly’s population is under control and only a few pest fly hosts are available, the female Fly Predator has the ability to reabsorb her eggs as a source of nourishment and thus is able to live up to a month while searching for pest fly pupae.

Fly Predators occur worldwide and in natural situations they are a major factor in the control of pest flies. However, where man has congregated domestic animals the presence of Fly Predators is often much more rare. One reason for this is that Fly Predators have not developed the immunity to pesticides that the pest fly has.

As there is no known method of fly control that offers 100% eradication of pest flies, Fly Predators do not totally eliminate the fly problem, they minimize it. Also, Fly Predators usually only disperse themselves 150 feet from where they have emerged, whereas pest flies migrate much farther, which means there will always be some pest flies coming in from neighboring uncontrolled breeding areas.

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For 42 years, tens of thousands of livestock owners have depended on Fly Predators. You can too! Try them and see what you could be missing...Flies!