I don't know how long, but just a warning, wash your hands very well after using them. Some people have allergies to them to varying degrees. When I started feeding my fish frozen bloodworms I must have gotten some of the juice in my eye. It itched like crazy and was red and puffy; it was not fun. I went to the doctor, thought I had pink eye. It was a big mess, took me a while to figure out that it was the bloodworms and that I am not alone in my allergy to red mosquito larva (bloodworms)