Found this hard, foam-like brown structure attached to a fence post in the backyard. I was about to scrape it off but hesitated. What is it?

Finding a strange, foam-like brown object on a fence post or a tree branch can be a very surprising experience. You might feel a bit nervous or curious, wondering if you should remove it or leave it alone. Before you reach for a scraper, it is helpful to know that you have likely found one of nature’s most interesting “nurseries.” What you are looking at is almost certainly an egg case from a praying mantis. In the world of science, this is called an ootheca. This structure is a vital part of a mantis’s life, and finding one is actually a…