Sydney woke up to moths on the windows — and that's wonderful news.

The Bogong moth is not much to look at — a plain brown moth with a two-inch wingspan — but it is the linchpin of an entire ecosystem. Each spring the moths migrate up to 1,900 miles to cool caves in the Australian Alps, where endangered pygmy-possums feast on them, and along the way they pollinate eucalyptus trees. Years of drought, intensified farming and habitat loss had thinned their numbers to a whisper. This week, Sydney and towns across southeast Australia woke to the moths blanketing homes and backyards in swarms, and authorities confirmed on Saturday that the endangered species is making a comeback. The jump in numbers is a positive sign for biodiversity, Victoria's chief biodiversity officer said — likely helped by extra rain in the north feeding the insects' larvae. The moths are harmless to people, and legally protected.