You hear cicadas every year because the ones singing outside your window aren’t the famous 13- or 17-year periodical cicadas. They’re a completely different group called annual cicadas, and their life cycles are staggered so that some adults emerge every single summer without fail. Individual annual cicadas actually spend 2 to 5 years underground as juveniles, but because their generations overlap, a fresh batch surfaces each year to fill your neighborhood with noise.
Annual vs. Periodical Cicadas
There are two broad categories of cicadas in North America, and they operate on very different schedules. Periodical cicadas are the ones that make headlines. They spend either 13 or 17 years underground, then emerge in massive synchronized swarms called broods. Almost every individual in a brood matures at the same time, which is why a periodical emergence feels like an invasion. In 2024, for example, two broods (one on a 17-year cycle and one on a 13-year cycle) surfaced simultaneously for the first time in over 200 years.
Annual cicadas are larger and greener than their periodical cousins, and they take a completely different approach. Each nymph still spends multiple years underground feeding on root fluids, but their emergence isn’t synchronized. In any given summer, a portion of the population is finishing its development and tunneling to the surface. The result is a reliable, every-summer presence rather than a once-in-a-generation event. Periodical cicadas are unique to North America, but annual cicadas thrive throughout the world, which is why people on nearly every continent associate summer with that familiar buzzing.
What Triggers Them to Come Up
Annual cicada nymphs don’t just crawl out on a random day. They wait for a specific environmental signal: soil temperature at about 8 inches deep needs to exceed roughly 64°F, typically after a rainstorm. That’s why emergence tends to cluster in the warmest stretch of summer, often July and August in most of the United States. These are sometimes called “dog-day cicadas” because they coincide with the dog days of summer. Once the soil hits that threshold and moisture loosens the ground, nymphs dig their way to the surface, climb the nearest vertical object (a tree trunk, a fence post, your porch railing), and shed their exoskeleton for the final time.
How They Make That Sound
Only males sing, and they do it to attract females. The sound comes from a specialized structure called a tymbal organ, a pair of ribbed membranes located at the base of the abdomen. A powerful muscle attached to each membrane rapidly buckles it inward and lets it snap back, producing clicks at such a high rate that they blur into a continuous buzz or whine. The abdomen itself is mostly hollow, acting as a resonating chamber that amplifies the sound far beyond what you’d expect from an insect.
That amplification is impressive. Close to a heavily infested tree, cicada noise can approach 100 decibels, comparable to standing next to a running lawnmower. The sound drops off with distance (about 6 decibels for every doubling of distance), so at 24 feet away you’d measure closer to 82 decibels. Still, anything at or above 85 decibels is considered hazardous to hearing over extended periods. If you’re spending hours in your yard during peak cicada season and the chorus is loud enough to make conversation difficult, wearing earplugs isn’t overkill.
Why Some Years Sound Louder
Even among annual cicadas, the volume varies from year to year. A stretch of warm, wet summers can boost nymph survival underground, leading to a bigger graduating class. Local tree health matters too, since nymphs feed on root sap for years before emerging. A neighborhood with mature hardwoods will support more cicadas than one with young landscaping.
Then there are the years when periodical broods overlap with the annual population. In those summers, you’re hearing two entirely separate groups at once. Brood XIV, a 17-year periodical brood, is set to emerge in 2025 across parts of the eastern United States. If you live in that range, you’ll get the usual annual cicadas plus millions of periodical ones on top. That combination can make a summer feel dramatically louder than the one before it.
Their Role in the Ecosystem
Annual cicadas are a major food source for birds, mammals, and at least one very specialized predator: the cicada killer wasp. These large, solitary wasps feed exclusively on annual cicadas. Females hunt them in mid-flight, paralyze them with a sting, and drag them into underground burrows to feed their larvae. The wasps’ entire life cycle is timed to annual cicada emergence, which makes sense when you consider that a wasp synchronized to periodical cicadas would starve waiting 13 or 17 years between meals.
Cicadas also give back to the landscape when they die. After mating and laying eggs in tree branches, adults live only a few weeks. Their bodies blanket the ground and decompose quickly, returning a significant pulse of nitrogen and other nutrients to the soil. The egg-laying slits in small branches can cause some tip dieback in young trees, but for established trees, the nutrient return more than compensates for the minor pruning.
The Overlap That Fools People
The reason many people assume all cicadas are on long cycles is that periodical emergences get enormous media coverage, while annual cicadas just quietly show up every summer without fanfare. When you hear cicadas in a non-brood year, those are annuals. When a brood year hits and the noise is overwhelming, you’re hearing both. The annual species never skipped a year. They were always there, singing from the treetops every July and August, forming the background hum so constant that you might only notice it when it finally stops in early fall.