Every year our white house is covered in black flies. The kids take fly swatters out and make a sport of killing 10 or 12 in one swat. Not this year.
This year I got on the Spalding Labs site to buy fly predators. When they arrived, we waited for them to start hatching then released them in groups in each of the recent grazing areas. The idea is that they will attack flies in the pupae stage, flying up to 150 feet to find more. Every 30 days through September the company will send more fly predators so every 30 days we’ll go behind the cows, dropping more predators on manure pats.
Fly populations are already getting strong but I hope we’re far enough ahead of the curve to have a fighting chance. I suspect we’ll have to start earlier in the spring next year. This year we’ll just run with what we’ve got.
Chism Heritage Farm 
Exactly what do they send you? That is, what is it that preys on fly larva in your area?
They ship sawdust and (infected? innoculated? fertilized?) fly pupae in a sealed bag. The instructions are on the back of the bag and say to keep the bag in a warm place until you see a dozen or so predators emerge then spread the contents of the bag where flies are likely to breed.
You’ll see tiny black flying things in the bag after a few days. They go out and lay eggs in the pupae.
Interesting. Hope it helps. I’ve always wondered with this sort of thing – what happens with the predator? Who eats it?
They are a naturally occuring predator, low fecundity and only live 50 or so days (See this link). That’s why they ship me new ones every month. I have to keep pushing up the population or they’ll fall behind. I have read a few people who suggest they reach a point where the population becomes self-sustaining but it may also be that they have good populations of other predators (swallows, frogs, spiders) and well-mineralized soils so pest populations don’t get so far out of whack. These ideas are covered well by Fias Co Farm.
Thanks for the link to Fias Co Farm – lots of great info there (and I love the name). We don’t have a lot of animals, and consequently, not a whole lot of flies, though occasionally, I feel compelled to put up some fly strips. Good knowledge to store away for the future, though.
We bought her herbal goat wormer for years. We also bought her goat milking stand plans. Good stuff on that site.
This is really good to know. Our laying hens follow our cattle around the farm to help control the fly population, but we only have one group of layers and 3 groups of cattle. Thanks for the info!