Theresa Westaby has no flies on her farm.

Wait… you might be thinking. What?!

Ok, “no” flies might be an exaggeration, but only a very…very…very slight one.

The Westabys, who are Organic Valley dairy farmer-owners in Illinois, have been using Spalding Fly Predators for 14 years, and they rarely see a fly buzzing around their heads or bothering their cows.

The Westabys' cows in their green pasture and not a fly in sight.

The Westabys’ cows in their pasture and not a fly in sight.

The Fly Predators are part of the Westabys’ integrated pest management (IPM) plan. IPM is a strategy that looks at the farm as a whole ecosystem and focuses on using various methods and working with nature to prevent and control pests rather than just one chemical method. IPM may include changing farm practices (such as how manure is managed), habitat restoration and conservation to attract beneficial insects and animals, setting up traps or giant vacuums, using organic-approved, naturally derived sprays on a case-by-case basis, and…introducing beneficial predators.

The Fly Predators are tiny wasps that lay their eggs inside of a fly egg. When the wasp eggs hatch, it kills the fly eggs, thus reducing the fly population on a farm. Simple!

Tiny Fly Predator wasps in a plastic bag, which arrived in the mail.

The Fly Predator wasps are 1/8 the size of a fly.

“They come every two weeks in the mail,” says Theresa, “and I take them out on the four-wheeler and sprinkle them all over the farm and around the pasture. I put them out in late April through September. Some survive the winters, which gets a head start the next spring before we get our first shipment.”

Over time, and combined with other techniques in their IPM plan, the fly population on the Westabys’ farm has dwindled to almost nothing! “We’re had them so long, we can sit outside, eat outside, and flies don’t bother us.

“It’s not just putting the Predators out there, though,” Theresa continues. “You have to keep things mowed and weed-whacked. You can’t let manure pile up where flies can get a jump on the Predators. Keeping the farm clean and neat makes a big difference.”

Calves eat hay in the barn and there are no flies in sight.

Calves in the barn, and not a fly on them.

Before the Westabys went organic, they had someone spray pesticides every two weeks from spring through fall, which cost them around $3,000—and that was only spraying the barn area. “It killed every fly in the place, but then in two weeks, the next eggs would hatch,” Theresa says.

The wasps, on the other hand, cost around $2,000 for the whole season, they cover the entire farm (not just the barn), and they don’t harm the people or other animals that call the farm home. “Once I release them, I hardly ever see them,” she says.

A calf lying in its pen in the sunshine and is not bothered by flies.

A calf enjoys the sunshine without being bothered.

As nice as it is for the humans, the cows receive the biggest benefit. “They’re much more calm because they can just go out and graze. They don’t have to be swatting at flies and shaking their heads,” says Theresa. “My daughter felt their production went up because they could spend more time laying down and chewing their cud, relaxing, rather than running around and burning energy getting away from the flies. Baby cows lay outside and there’s not a fly on them, and before there would be flies coating the front of their pens.

“It takes consistency, putting them out year after year, but over time and with keeping the farm clean, they take care of all the flies. To me, it’s money well-spent!”


Want more? Read more fun and quirky animal care stories in this series! 

Did you know Theresa Westaby is also a Rootstock contributor? You can read her stories about farm life here.