They spend most of their time buried in the sand, with only their siphon extending above the substrate. Because these snails have an incredible sense of smell, they quickly detect any food introduced into the aquarium, and cause the substrate to "boil" as they emerge in search of food. They quickly consume detritus, uneaten food, decaying organics, and fish waste before they can be broken down by bacteria and release excess nutrients in the system. In addition, while burying themselves they aerate the sand bed/substrate, which helps maintain adequate oxygen levels in the substrate.
Picture above is of one of mine laying eggs on the glass. It lays them all the time, but nothing ever comes of it.