They are a high calcium, high protein feeder insect, also known as black soldier fly larvae (Hermetia illucens). They can be used as a treat for reptiles, birds, fish, spiders, tenrecs and other insect loving animals. They have 50x more calcium than other feeder insects, so there is no need to add calcium powder.
They also make a great live bait for fishing. Fish are drawn to the smell, sight and movement of the worms in water.