“The pupa is enclosed in a round brown cocoon, attached often to the stem of the food plant, usually eucalyptus species. The caterpillar coats the cocoon with a special liquid which makes it hard and smooth. The cocoon has a ring of weakness around the top. Later, when the adult emerges, it does so by breaking the cocoon along the ring, pushing off a rounded cap and leaving behind a little cup (hence the name) with the empty chrysalis.” Image taken on Swamp Turpentine sapling at Sportsman Creek wildlife refuge late summer.
Reference and I.D. courtesy of Don Herbison-Evans.