One of nature's enduring enigmas is making an appearance once again, bringing a sibilant drone to the towns of Cape Cod, as it has every 17 years with startling regularity. Insects known as periodical cicadas are emerging from underground haunts for a final hurrah - a nearly monthlong orgy of come-hither songs, mating, and laying eggs - before dying and leaving their progeny behind to begin anew the curious and highly unusual 17-year growth period. Residents are bracing themselves. "We're thinking about moving to Boston to live with my daughter!" joked Jeanne Duchemin, of Mashpee, who recalls the inundation of...