This process is called sublimation. The opposite (deposition) is where a gas turns directly into a solid. Sublimation occurs if the pressure and temperature are right for the specific substance, so that the solid phase in a phase diagram borders the gas phase.
Most cicadas go through a life cycle that lasts from two to five years. Some species have much longer life cycles, such as the North American genus, Magicicada, which has a number of distinct broods that go through either a 17-year or, in some parts of the world, a 13-year life cycle.
Why do these things only come around once every 17 years? Not all cicadas have a 17-year life cycle. Some, dubbed annual cicadas, have life spans of anywhere from two to eight years, and some members of these species end up emerging every year, so they're not as noticeable. The cicadas we'll see this year, however, are periodical cicadas. Some species have a 17-year life cycle, while others are on a 13-year cycle.