Han dynasty (206 BC - AD 220)
For protecting the dead
The cicada often appeared on birthday gifts in China, representing wishes for the recipient's longevity. In death, the cicada may have stood for resurrection. Jade has always been highly valued in China, in this life and for use in the afterlife. It was thought to have special powers, possibly protective ones. The Chinese believed that, after death, it preserved the corpse. Cicadas made of jade were placed on the corpse's tongue before burial. Sometimes glass was used as a less expensive substitute.
The Chinese placed jade objects in their tombs as early as the Neolithic period (about 4000 BC). Jade was first used to cover specific parts of the body during the Western Zhou dynasty (1050-771 BC). In the Han dynasty (206 BC-AD 220), the practice arose of the plugging of the corpse's nine orifices with jade. The cicada was placed on the tongue, plaques covered the eyes and plugs filled the nose and ears.
J. Rawson, Chinese jade: from the Neolith (London, The British Museum Press, 1995, reprinted 2002)