They're the Rip Van Winkles of the bug world and they're back. One of the largest groups of periodic cicadas is beginning its loud, ugly and clumsy life cycle. It will last just a few frenetic weeks before they dig in for another 17-year snooze. Indiana biologist Keith Clay says cicadas are amazing but still produce a "yuck factor." Though harmless, (m) millions of cicadas will blunder into pets, bushes and unwitting pedestrians during their frantic mating ritual. They're only seen east of the Great Plains. This year's group is the largest of several and is concentrated in the Midwest and the mid-Atlantic. The insects are a treat for robins and other birds, and even some pets, who are at risk for diarrhea or constipation if they eat too many. But sheer numbers ensure the cicada's survival.