What Are These Grubs Called?

Last summer, I found these larvae, or grubs, or whatever they are called, living underneath and inside a black plastic bag I put broccoli plants in to kill the caterpillars that were feeding on them. Not having chickens at the time, I found them disgusting and imagined they would become another plague to attack my garden. I killed as many as I could, but I continued to find a few of them in the compost pile. I didn’t worry too much about it, because I hadn’t seen an influx of the creatures.

This summer, I have chickens, and I have found masses of the creatures happily wiggling in my compost. I test the chicken’s appetites on any critter that I don’t think is a beneficial insect, and they love these things.  I just don’t know what they are called. They prefer hot locations, like under a black plastic bag in the sun, and in the middle of a compost pile that’s becoming hot from the biological activity. I can’t see any harm they do, and the chickens love them, so I like their presence.

I wonder if they are Black soldier fly larvae, but my husband says he thinks they are too big to be a fly. The largest ones are about 1/2 inch long. He thinks they are a beetle. If you have any ideas, please let me know.