Cicadas typically emerge from the ground in periodic cycles that depend on the species. The most well-known periodical cicadas come out every 13 or 17 years. These cicadas spend most of their lives underground as nymphs, feeding on tree root sap, and then emerge synchronously in large numbers during late spring or early summer when the soil temperature reaches about 64°F (18°C) at around 8 inches deep

. There are two main types of periodical cicadas:

• 17-year cicadas : These emerge every 17 years in large broods. For example, Brood XIV is expected to emerge in spring 2025 in parts of the eastern U.S., and Brood X emerged in 2021

• 13-year cicadas : These emerge every 13 years, such as Brood XIX expected in 2024 in parts of the Midwest and Southeast

The emergence period lasts about 4 to 6 weeks, during which cicadas molt, mate, lay eggs, and then die. The eggs hatch within a couple of months, and the new nymphs burrow underground to begin their long developmental cycle again

. In addition to these periodical cicadas, there are also "annual" cicadas- about 163 species in the U.S.-that emerge every year, which explains why people hear cicadas every summer even though the famous 13- and 17-year cicadas appear only periodically

. In summary, the famous periodical cicadas come out either every 13 or 17 years depending on their brood, while other cicada species emerge annually. The 13- and 17-year cycles are adaptations to avoid predators by emerging in massive numbers simultaneously, overwhelming potential threats