Milk worms are squirmy, symbiont worms which enjoy milk and warmth and in return secrete hormones that cause more milk and bigger boobs the longer they're in. And they're quite sapient, too, and will listen to what they are told by the host.

Their appearance is of a smooth, completely white worm, and have 3 black eyes on their front.

These were originally made by the Artist scruffythedeer (https://e621.net/artists/13061).