Fly reproduction is sensitive to moisture. The larvae (maggot) will only successfully reproduce in rotting organic material and manure that has between 40-60% moisture content for at least 3-5 days.  With excessive rain, far more material will stay in that ideal moisture range longer than normal. This can result in a huge increase in flies, particularly Biting Stable Flies in spring.
Pay attention to those areas with decaying vegetative matter such as drainage ways, ditches, grass clippings and hay chaff.  This type of material can breed an excessive number of Biting Stable Flies even when no manure is present.
To help reduce the influx of flies, consider increasing your next shipment of Fly Predators or adding an additional shipment to have extra Fly Predators to spread in those areas staying wetter than normal. 
Also, no matter how many years you’ve been using Fly Predators, anyone can gleam helpful tips from our How To Use Fly Predators video.
If this these images ↑ remind you of your Spring weather, give us a call at 800-737-2753 to speak with a Fly Control Expert. We have several tool to help get things back to normal for you. ♥