a cicada, Magicicada septendecim, of the eastern U.S., having nymphs that live in the soil, usually emerging in great numbers after 17 years in the North or 13 years in the South.
British Dictionary definitions for seventeen-year locust
seventeen-year locust
noun
1.
an E North American cicada, Magicicada septendecim, appearing in great numbers at infrequent intervals because its nymphs take 13 or 17 years to mature Also called periodical cicada