Odd timing keeps cicadas in their prime

摘要

The strange underground life of periodic cicadas, insects that enclose themselves in a burrow for either 13 or 17 years virtually to the day, has long intrigued biologists. Now a researcher in Japan believes that their life cycle is a genetic hangover from their struggle to survive the ice age. Of about 1500 known species of cicada, only a handful, all in the genus Magicicada, are periodic. When the nymphs hatch, they burrow into the ground, and remain there for exactly 13 or 17 years, with northern populations staying underground longer. The fully grown adults then emerge simultaneously.