China exports tons of frozen earthworms annually. Frozen earthworms are available in Europe as a fish food and fishing bait.
I wouldn't think the expense to freeze-dry earthworms would yield a viable product. Earthworms are larger than other available FD foods and would require additional dry ice and air time. However, earthworms are being dried (in those Ronco food-drying type machines) just like fruits and veggies. The cost is low and the shelf-life can be a couple of years with seal-a-meal bags.