Like the fabled Rip Van Winkle, who slept for 20 years while the world passed him by, millions of insects in our area will noisily emerge this year after years of silent dormancy. Brood X of the periodical cicada, which has the largest emergence for the 17-year cicada in the U.S., is expected to return this spring and summer after its last appearance in 2004. The cicada, a 1.5-inch-long flying insect, has the longest developmental period of any insect in North America. When first hatched, they burrow into the ground and attach to roots, where they feed on sap and grow for 13 or 17 years, depending on the type.