On 17 March 2020, I found a European Mantis ootheca under the bark of our Silver Maple tree.
I took it inside and put it in a glass terrarium to see if some of the eggs would hatch later in the spring.
I was beginning to give up, but on Mother's Day they began to hatch.
Several dozen or so of these little guys (~ 5 mm) emerged from the ootheca, leaving their shed exoskeletons hanging from the bark. I tried feeding them some earthworms, slugs, and pillbugs that I found in the dirt outside, but they all dried out and died before the tiny mantids could find and eat them. So I released them all under the maple tree where I found them nearly two months before.