I bought small silkworms for my 5 and 6 month old chams. Two of them like them and the other might eat one if I am lucky. The silkworms are growing so fast that now I have very few small ones and most of them have gotten too big too feed to the chams. How long do they last when they get to full grown size? I don't know how big they can get before I can't give the chams anymore.