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Well, I think a bucket with rotten plant material with some added water left in the rain is not different from fresh cow pads.

Thoracochaeta zosterae is a sphaerocerid which is particularly known from beaches where the larvae live in rotting see weed. The species is also found inland along rivers, etc., but much scarcer. I found them in a bucket which had a lot of glass tubes with some agar at the bottom in it. I was just waiting for the agar to become soft enough to clean the tubes and I left the bucket outside in the sun. From unknown distance (but the rive Rhine about 5 km away) flies must have located the bucket and deposited eggs.