I discovered a Cicada shell in my backyard on the weekend when I was trimming the hedge.
Cicadas live underground as nymphs for most of their lives, at depths ranging from about 30 cm (1 ft) down to 2.5 m (about 8½ ft). The nymphs feed on root juice and have strong front legs for digging.
In the final nymphal instar, they construct an exit tunnel to the surface and emerge. They then molt (shed their skins), on a nearby plant for the last time and emerge as adults. The abandoned skins remain, still clinging to the bark of trees.