I use a small coffee cup, put two layers of saran wrap on top, rubber band to hold the sarah, and poke a hole in the top for the stem of the milkweed or leaf. I have learned that cutting off the very top of a milkweed plant is best when the cats are larger, like 1" or so. That gives them more leaves to eat before I have to change it. If you have an egg or tiny baby on a leaf, and don't want the whole stem and all, cut the bottom of the leaf back so there is at least 2" of stem on the leaf, and put it in the water. Using wet paper towels wrapped in saran or foil works, but only for a day or so. The leave/stem needs to be in water if possible. I have mine in a 10 gallon aquarium, and if I get many more cats, I'll be putting them into my empty 55 gallon. I raised 42 cats last year, and this year I have a total of 3 in chrysalis so far, and 8 more in all stages. That's doable in a 10 gallon, but if I bring in the "beast" 55 gal, I'll have much more room to make sure to keep the tiny babies separate from the larger ones, as the larger ones might eat the leaf the baby is on, and eat the baby, too! Good luck!!!