[Naturens] worms in compost

Hello, Sometimes I find a writhing wad of the smaller red earthworms right on the rim of my typical black compost bin. The compost might be only halfway up the sides, so they have deliberately and concertedly made quite a climb. What for? There are pockets of them wadded together down in the compost as well, for instance inside a rotted-out avocado pit or hollowed corn cob, so they can be close without meeting up on the rim. Thank you for your insights, Nancy Roberts