California Riding Magazine • March, 2008

No-Fly Zone
Fly Predators and simple stable maintenance prevent pesky problems before they start.

When it comes to fly control in a stable environment, the best defense is a good offense. That’s the premise that has made Spalding Labs a big friend to horses, their owners and their neighbors for the last 32 years. The company’s Fly Predators are beneficial insects that, as their name suggests, prey on flies. Unable to form cocoons themselves, the Predators burrow into the flies’ cocoons to lay their offspring. In doing so, they destroy the immature fly and thus prevent a future fly.

Educating people about the fly’s life cycle and habits is the core of Spalding Labs’ sales pitch. “People can do a lot of simple things, without even buying our product, to reduce their fly population,” says Tom Spalding, who calls himself the “chief fly guy” at the family-owned business.

For instance, not everyone knows that the area around a leaking water bucket can be a “fly factory,” he says. Knowing what kind of flies you are dealing with and where they come from is the first step. Spalding Lab’s 32-page booklet includes descriptions of the three main types of flies that pester horses. “It’s important to match your flies with where they come from,” notes Tom.

The most common, usually referred to as the House Fly, breeds in manure. The Stable Fly, which “bites like the dickens,” breeds in rotting vegetation, like spoiled feed. Another fly, the Horn Fly, is only a problem for those who keep horses near cattle. It breeds in undisturbed cow pies. Spalding Labs’ Fly Predators will take care of all three flies if they are put in the locations where each breeds.

Flies need moisture to reproduce. The moister it stays, the longer manure remains viable for flies, which explains why rainy seasons are often followed by especially bad fly seasons. Spreading manure out as much as possible to dry it within five days greatly reduces the pests’ ability to reproduce. Leaky water buckets or pipes are other culprits to seek and fix if flies persist.

Taking advantage of the fly’s life cycle is another key to maintaining a fly free stable. It takes at least five days for the fly to get to the cocoon stage and at least eight days for an egg to hatch into an adult fly. Getting manure properly spread and dried out, or removing it from the property, before those cycles complete is essential.

“If you can get the manure to dry below a 40 percent moisture level, the fly cocoon won’t be able to form,” Tom explains. Better yet, get the manure off the property. “If you leave the manure in the dumpster for two weeks, you assure yourself of allowing those flies to make it.” If that is not an option, move the manure pile as far away from stable activity as is possible. House flies can travel about a quarter mile, Tom reports, so if the waste can be located beyond that range, most of the new flies will be out of reach. Stable flies can travel considerably farther.

If removing the manure is not possible, forming a big manure pile is the next best thing. The heat inside is too hot for flies to develop and only a six-inch layer on the surface of the heap is viable for fly growth.
Although one pair of breeding flies can produce approximately 900 eggs, half of which are typically female, the survival rate is between just two and four percent due to predation from beneficials like Fly Predators, plus beetles, mites, birds, ants and environment factors like moisture, temperature and food source. Reducing moisture and removing manure slash that rate even further. So can adding more Fly Predators.

For the cost of $2 to $4 per horse per month, regular dispersals of Fly Predators reduce fly populations so effectively that some customers have all but forgotten about the pests. Left alone, a native population of Fly Predators doesn’t want to totally eradicate the fly population because they rely on them to lay their own eggs. By regularly adding Fly Predators to the flies’ breeding areas, the over abundance of Fly Predators creates enough competition to ensure that close to all the flies are killed before they emerge from the cocoons. The process enables fly prevention, rather than remediation by bait or sprays after there are already too many, Tom notes. Fly Predators are virtually unnoticeable because they are tiny and stay near manure.

Little use for chemical pesticides and fly sprays are a side benefit of using Fly Predators. “We were green before it was cool,” says Tom. But environmental friendliness wouldn’t mean much if the product didn’t work. “We work better and we’re green.”

Spalding Labs got its start solving the fly problem the family had while raising Arabians in their Monrovia hometown. “My brother read the research on beneficial insects that was being done at U.C. Riverside and he decided to try it,” says Tom. “He released them on our farm and it made a huge difference.” Thirty two years later, Spalding Labs’ website is filled with similar testimonies from horse owners in every climate in the United States.

For more information on Spalding Labs, visit