Thank you America for growing your population so large. When climate change gets so bad that the dykes pop, we can just grab the nearest American to plug the hole and save humanity.
Various ant species do a similar thing where their soldiers have really big, flat heads and when their nest gets attacked, the soldiers stick their head into the entrance way, so the attackers can't come inside.
Apparently, this kind of behaviour is referred to as phragmosis.
Not OP, I couldn't find a paper. Just this site that makes the same claim almost word for word, and cites a youtube video of a lecture at Stanford. I didn't watch the video, but this seems best described as a "plausible" explanation rather than a proven fact.
The more I read about them, the more I'm fascinated with how alien they seem to be to me. It's either them or crabs as the ultimate form that everything would come to eventually. Maybe even molecrabs we are yet to discover.