Hello Peter and Stefanie,
The glass worm are sold in a wet newspaper, its quite a large quantity (100grams of worms), so I throw them in a bucket rainwater and keep them outside. I order them from a killifish breeder who made a small business out of selling fish, eggs and supplies.I could ask him about the origin, but so far I never had problems whit those.
I never use the normal plastic bags of life food, and reading all this makes me sure to keep it that way.
Most time of the year I can catch enough food whit all the ditches in the area. somehow I never catch a lot of glass worms despite massive amounts of Daphnia and Cyclops.
@ Sverting,thnx! They look nice indeed, I’ll see if I can find them.