The "Sitters" are an extraterrestrial race of strange beings which need no physical nourishment; instead, they thrive by consuming beauty and youth. Things like the prettiness of a flower bouquet or the laughter of children playing are all they need to survive.
Physically, they appear like short slim humanoids with an appearance that exhales sweetness, grace and innocence. They have curious skin arrangements on their heads which are reminiscent of flower petals.
Three members of this species were brought to Earth after making contact with space pioneer Lamont Stiles in one of his travels. They would go on to reside on Stiles' hometown of Millville, where they found employment as babysitters. Eventually, Stiles left Earth for space again, leaving his house for the Sitters, and letting them turn it into a nursery.
Since they have no need for money, the Sitters will accept as payment anything which contains beauty in it, such as flowers, perfume or any nice-looking objects. The town's residents are more than happy with this arrangement, though they're not aware of the Sitters' actual source of nourishment.
- The Sitters, by Clifford D. Simak (1958)