These tiny insects search out and kill developing flies and significantly reduce numbers of adult flies that can pester your livestock. By simply spreading the fly parasites around common fly breeding sites significantly fewer flies develop to adulthood. Fly parasites feed only on developing nuisance flies and don’t bother your cows themselves. This means your cows have more time to eat & produce milk. Unlike other pour-on type products fly parasites don’t depend on flies having to bite cows before they work.