Q: There are small flying bugs that are turning horse manure into large areas of flattened mush. There are hundreds working on each pile. Do you know what they are?
A: Your "bugs" are actually small dung beetles or Aphodius haemorrhoidalis. We researched them in cow dung 15 years ago and found they were most abundant in spring, and tapered off in the fall. The ones you are seeing descended from a bountiful summer population and they are working on your horse's manure to build up nutrients for overwintering.
The beetles are actually beneficial; they spread out the manure, which speeds incorporation into the soil, and break up piles. It is possible that internal parasites eggs in the manure could become more spread out. However, any increase in parasite transmission would be minimal if you routinely deworm your horse(s).
By Roger Moon, PhD, University of Minnesota