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.