Paper bag experiment is done.
My experiment with raising cats in paper bags is over, and I thought I'd reflect on the pros and cons of it. The reader should keep in mind that Sandy (butterflymomok) is the expert on this and probably has solutions to some of the issues I raise below.
My procedure: take small cats or eggs on whole leaf off of plants and put into plastic glad containers, 10 cats/container. Strictly regulate age so that all cats are +/- 3 days of each other. Leave them in until 3rd instar, replenishing food and counting cats daily.
At 3rd instar, transfer cats to paper bag, with whole plant sprigs in water pics, supported by Dixie cup. Check food and count cats daily. Cats should pupate on side of bag (but see below...).
At pupation, cut small paper square around the cremaster and tape the paper to top of cage or other container for pupation.
Results: I raised 21 caterpillars in bags until the last instar and into pupation in about half of the cases.
The biggest pro to the bag method is hygiene. When raising in cages, I feel nervous about the possibility of NPV or OE making it through the cage. In bags, a disease is self-limiting. This is a large advantage for those whose populations are 100+ cats.
Other pros: Surveys were easy to make accurate. The cats were well-protected (0 losses). Cat poop is contained and does not need to be cleaned out, since the bag is discarded after the cats pupate.
The biggest con is population control. Because the caterpillars sometimes migrate to the top of the bag, and because I'm hesitant to move a stationary cat lest he be preparing to molt, I ended up not being able to secure the bags tightly. In other words, I had to trust that the cats would stay near their food source.
Twice, that assumption failed. I had one escapee two days ago (15 minute search; he had crawled up the china hutch). Then, today, I came home and found that six (!!) cats had escaped looking for places to pupate. One attached to the wall, one to the china hutch, one to another paper bag, and another to my microscope. As a result, I transferred the 10 remaining last-instar cats into the cage for safe-keeping.
Sandy double-folds the bags and clips them with document clips, but I was not comfortable making a tight seal with cats near the top. So ...
Additional cons: We don't really have a lot of inside storage space, and I don't trust bags outdoors what with wind, water, and sun. Also, getting food in and out of the bags is less convenient than in the cage.
Actually, food is a big issue. In the cage, I can "load up" a group of 21 cats with 7 or 8 stems of milkweed on a couple of Glad containers and then basically check every day to see that the food is still ample -- a 2 second scan, or 2 minutes if I do a cat count. Adding new food is simply a matter of adding a new stem to the container or putting a new container in the cage.
In the bags, I have to open each bag, count the cats, and pull the Dixie cup out in order to change out the food -- which is challenging in the limited space of the paper bag, especially when there are two chrysalises on the side and three large cats on foodplants.
Finally, the process of transferring pupae from bag to cage is clumsy, and I don't entirely trust the tape to hold the pupae to the cage.
So in the end, I will hybridize the methods. I'm totally sold on keeping small cats in containers; but after 3rd instar, I'm going to transfer them to cages.