Caterpillar Setups > Netted sleeve
An alternative is to create a pull-string nylon net sleeve and place this around a branch with caterpillars. This also saves the time of cleaning out frass and changing out host plant cuttings.
The drawback to this technique is that spiders can smell caterpillar frass and still kill butterfly caterpillars if they are too close to the sleeve. Parasites are also a major concern. Make sure that the sleeve is completely secure from predators or parasites that can enter and kill your larvae. See this video.
Gregarious caterpillars like mourning cloaks (Nymphalis antiopa) or California tortoiseshells (Nymphalis californica) that feed on leaves of deciduous trees can easily be reared using caterpillar sleeves. These sleeves can be sewn at home or are available online.
Mojave sootywing (Hesperopsis libya confertiblanca) caterpillars will often partially aestivate at fourth and fifth instars making the open terrarium technique of rearing somewhat problematic. A practical alternative is to simply place larvae on a larger bush, and then sleeve the branch of saltbush (Atriplex confertifolia).