HN removed a leading "how", which in this case hurt the title. It's a fascinating research article -- the link itself is just a few paragraphs but it links to the full paper which is free!
https://www.youtube.com/watch?v=ORPEL30Wrzk
What's cool is how the ants keep airbubbles around them so if you push the whole raft underwater, it turns into a ball and keeps an air bubble around it. Really amazing stuff!