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?

Coming across a strange structure in your backyard can spark both curiosity and concern. Maybe you’ve noticed a firm, brown, foam-like mass clinging to a fence post or tree branch. At first glance, it might seem suspicious—something harmful or invasive. But before you rush to remove it, it’s worth understanding what it actually is.