Stable flies can make life miserable for livestock. One way to control the pest is releasing a parasitic wasp that does not sting people or animals, but will kill the flies. Credit: Elissa Ballman / BDN

It’s an inescapable fact that where there are animals or birds, there is going to be manure. And where there is manure, there are blood-sucking stable flies. But a certain species of parasitic wasp can help fight against disease-carrying flies that hurt livestock and poultry.

Blood-sucking insects are a serious problem. The United States Department of Agriculture estimates diseases and stress from their bites causes $2 billion in livestock and poultry damages annually around the country. Stacked up against those losses, the cost of a few thousand parasitic wasps can be a small price to pay for a non-chemical fly control. Available online, spalangia parasitic wasps can cost around $16 for a package of 15,000.

No figures were readily available on livestock or poultry damage from stable flies here in Maine, but according to Jim Dill, pest management specialist at University of Maine Cooperative Extension, the bites from stable flies can interfere with dairy milk flows.

“If you have stable flies, they bite and that will bother the animals and will draw blood,” Dill said. “If it gets bad enough, it can impact milk production in dairy animals.”

The incessant buzzing of flies around humans, livestock and poultry can also just be a major annoyance, he said.

“You also have to figure they do carry disease,” Dill said. “They are climbing on and in manure and there is every chance they are picking up things like salmonella then fly off carrying the disease to other places or animals.”

To combat the stable and house flies, Dill said controlled release of tiny parasitic wasps is a proven strategy.

“We did some work with [parasitic wasps] here at extension years ago,” he said. “It can work fairly well.”

When purchasing parasitic wasps, Dill said it’s a good idea to buy from a source located in New England. That’s because they have evolved to be the most effective parasites on flies from this area.

When you place your order, Dill said the seller should be able to help determine how many wasps you need based on the number of animals and birds you have.

“You buy them, release them and they will go into the manure and sting the stable or house fly pupae,” Dill said. “They then lay the eggs inside those pupae.”

As the wasp eggs hatch and develop into adults, they kill the host fly.

“When the wasp emerges from the fly, they go off to find and kill more,” Dill said.

Parasitic wasps take about three weeks to complete a generation, while flies that can take less than 10 days. So multiple releases of wasps during fly season is more successful than releasing a large population all at once.

Even though you may be releasing tens of thousands of wasps into your barn, horse stalls or chicken coops, they are not going to bother anyone or anything other than stable and house flies.

“They are so small you probably won’t even notice them,” Dill said. “They don’t sting people or animals.”

Also, be sure that your manure is ready for the wasps, which need specific conditions.

“The big key to any of these parasitic wasps is keeping manure dry,” he said. “The dryer the manure, the less successful flies will be and the better job killing them the wasps will do.”

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.