Earthworms have a unique ability to tie themselves into knots, but they do it on purpose. During droughts, tying themselves into knots reduces their surface area, allowing them to burrow deeper underground and retain more moisture. This is a type of summer hibernation called “activation”.
However, not all worm knots are beneficial. Some much smaller worms, called nematodes, can get infected by bacteria that inflate their butts and tie them together to form “worm stars”. When multiple worms are bound together, they lose their structural integrity and become immobilized, becoming food for the bacteria.