Verified answer

"They feed on plant roots digging deeper into the soil and using larger roots in successive instars. Feeding, in both nymphs and adults, is done by penetrating the XYLEM not phloem as is the case with most sap sucking insects. This gives them a very watery, low sugar and high amino acid diet. The larvae build themselves cells to live in, often using the excess excreted moisture resulting from their feeding to cement the walls of their cells together. Generally cicada nymphs go through 5 instars.

Adults feed on Xylem the same as the nymphs."

http://www.earthlife.net/insects/cicadidae.html

Unless you can tempt them by offering a tree, you're pretty much out of luck.