Chicago -- Experts said 17-year cicadas have been spotted in the Chicago area, one year after the rest of their brood emerged to mate and die.

Gene Kritsky, of the College of Mount St. Joseph in Cincinnati and author of "Periodical Cicadas: The Plague and the Puzzle," said some of the 17-year cicadas, which are believed to measure time by the fluid flow in trees, apparently have faulty internal clocks that led them to emerge a year late, the Chicago Sun-Times reported Friday.

"Eighteen calendar years went past but the cicada detected 17,'' Kritsky said.

Kritsky told the Sun-Times five Chicago-area residents have reported spotting 17-year cicadas, which are characterized by their red eyes and smaller forms than their cousins, the annual cicadas. He said the most recent report came on July 19.

Copyright 2008 by United Press International.