hibernaculum

hibernaculum \hahy-ber-NAK-yuh-luhm\, noun:
1. a protective case or covering, especially for winter, as of an animal or a plant bud.
2. winter quarters, as of a hibernating animal.
Already it has become something much greater than a house or a home: a hibernaculum, for each of them, of some kind of ecstatic regeneration.
-- Kate Moses, Wintering: a Novel of Sylvia Plath, 2003
This winter home or hibernaculum of the peach-tree borer is a thin affair, with a smooth interior, and is made of bits of frass or particles of bark fastened together with silken threads, which simply covers the borer as it rests curled up on the bark.
-- Mark Vernon Slingerland, The Peach-tree Borer, 1899
Hibernaculum comes from the Latin hībernāculum meaning "winter residence." It entered English in the late 1600s.