At our last Backyard Herbalist class, one of my students gave me a bag of praying mantis egg cases... the praying mantis has a long Latin name just like plants do... Tenodera aridifolia sinensis. They are carnivorous insects that will feed on almost any other insect they can overcome, including their own kind.
The case is a mass of hardened foam containing from 50 to 400 eggs, that the female secreted on twigs in late summer or autumn.
Purchased cases can be kept in a jar in the refrigerator until you want to release them in the spring. Attach the egg case to a stem a few feet off the ground.
I can have fun observing this case for signs of a hatch while I work on cleaning up the flower bed this weekend. Actually, the case doesn't change in appearance once the young hatch, and it may take up to 8 weeks, but I'll be around and looking for these interesting "pet bugs."