I found this strange cocoon attached to a bush in my yard. I thought that would kill the bush so I removed the twig and brought it into the house to study it. It turned out that it was the egg sac of a praying mantis called an “ootheca.” Rather than hatch the babies in my house, I attached it back to the bush with a zip tie.
The mother mantis lays her eggs in the fall before the first freeze. She produces proteins that make a foam around the eggs and then harden into the protective ootheca. Each ootheca contains about 50-200 eggs. The mother dies after making the egg sac. Over the winter, the eggs develop into babies.
In the spring, when the temperature is around 70-80 degrees and humidity less than 50% for about two weeks, the babies hatch inside the ootheca. Then they chew through the wall to get outside and eat small insects like aphids and fruit flies. If they don’t get out of the ootheca fast enough to eat, the bigger babies may eat the smaller ones. The babies are about 4mm (1/8 inch) long.
https://praying-mantis.org/what-do-baby-praying-mantis-eat/ This link shows someone feeding a fly to a baby mantis.
Praying mantis are carnivores. The adults eat grasshoppers, crickets, beetles, flies, bees, wasps, butterflies, gnats, and occasionally a small hummingbird or a small snake.
Another type of insect that makes and ootheca to protect the eggs is a cockroach.



