The insects people describe as coming out every seven years are usually periodical cicadas, but seven years is not the usual interval for the best-known North American broods. Those cicadas spend most of their lives underground and emerge together after a longer, species-specific cycle—most commonly every thirteen or seventeen years.
What “every seven years” usually means
There is no famous, standard group of periodical cicadas that reliably appears every seven years across a broad region. The familiar mass emergences in eastern North America belong chiefly to species with thirteen-year or seventeen-year life cycles. People may hear about a seven-year interval because they have seen cicadas in different years, confused a local emergence with a full cycle, or encountered a report about a different insect.
“Come out” is also an imprecise description. A cicada does not spend its entire life hidden and then suddenly appear as an adult. It begins life as an egg, hatches into a tiny nymph, drops to the ground, and lives belowground while feeding on fluids from plant roots. When its development is complete, it climbs out, sheds its nymphal skin, and becomes a winged adult.
Periodical cicadas are not the only cicadas. Annual cicadas appear in summer in many places, often in smaller or less synchronized numbers. Their nymphs still spend years underground, but adults from overlapping generations emerge each year, making the species seem annual. That difference helps explain why one person may hear cicadas every summer while another waits years for a conspicuous mass emergence.
How periodical cicada cycles work
The long underground stage is the defining feature of periodical cicadas. Nymphs feed on xylem fluid from roots, grow through successive developmental stages, and remain out of sight. Near the end of the cycle, mature nymphs emerge from the soil, often after the ground has warmed in spring. They climb vegetation or other surfaces, split their nymphal skins, and expand their wings as adults.
Once aboveground, adults have a brief reproductive phase compared with their long nymphal life. Males gather and produce loud, species-specific calls; females respond and mate. Females lay eggs in slits made in small branches. After the eggs hatch, the young nymphs fall to the ground and burrow in, beginning the next generation.
The adult stage is conspicuous but temporary. It is the synchronized appearance of many insects at once—not the whole life cycle—that people notice as an “emergence.” The adults feed little or not at all compared with the nymphs, and their central tasks are reproduction and laying eggs.
Why the cycles are thirteen or seventeen years
Scientists have proposed several explanations for the unusually long cycles and synchronized emergence of periodical cicadas. A leading idea is that spending a long time underground helps them avoid predators and unfavorable conditions, while appearing in huge numbers briefly can overwhelm the predators that do find them. The timing also makes it less likely that a predator can depend on cicadas as a regular food source.
The prime-number cycle lengths may help different broods avoid repeatedly emerging in the same years as other broods. A thirteen-year cycle and a seventeen-year cycle line up relatively infrequently compared with many shorter cycles. This is a useful explanation for the pattern, but it should not be treated as a complete, settled account of every evolutionary detail.
Climate and local conditions influence when cicadas become active, but a warm spring does not simply reset a brood’s long-term schedule. Emergence timing is associated with the insects’ development and seasonal cues, and local reports can vary by place. A few early or delayed individuals do not necessarily mean the whole brood has changed its cycle.
Broods, species, and local emergence
A brood is a population of periodical cicadas associated with a particular emergence year and geographic area. Brood labels help researchers and observers distinguish these regional populations; the label is not the name of a species. Different broods can include more than one cicada species, and neighboring areas may have different emergence schedules.
Because the insects are regional, a cycle reported for one state or county does not automatically apply elsewhere. A person can encounter annual cicadas during a year when no periodical brood is emerging nearby, or miss a major emergence by traveling outside its range. Local natural-history organizations and government extension services can help identify what is expected in a particular area; check current local information rather than relying on a broad national headline.
Periodical cicadas are native insects, not a sign of an infestation that has recently spread everywhere. Their familiar mass appearances are part of a long-running biological cycle. The loudness and abundance can be striking, but the insects generally do not bite or sting people.
How to distinguish periodical and annual cicadas
Appearance alone can be misleading, especially because cicadas vary among species. Timing and local abundance are often more useful clues. Periodical cicadas tend to emerge in large, synchronized groups in their range, while annual cicadas are heard or seen in many summers because different individuals or species mature at different times.
- Timing: A sudden, region-wide surge after years without a comparable emergence suggests periodical cicadas; familiar summer calls each year are more likely to come from annual species.
- Numbers: Periodical emergences can produce dense concentrations of adults and shed skins in affected places. Annual cicadas are usually less synchronized.
- Local reports: A confirmed brood map or local observation can clarify whether a periodical emergence is expected nearby.
- Life history: Both kinds have underground nymph stages. “Annual” does not mean an individual cicada necessarily develops from egg to adult in one year.
These are practical clues rather than a substitute for identification. Several cicada species may occur in the same broad region, and observers should avoid assuming that every loud summer insect belongs to a periodical brood.
What an emergence means for trees and gardens
Adult cicadas are not generally considered dangerous to people, pets, or established trees. The main plant concern comes from egg laying: females cut slits into branches, and heavily used small branches may wilt or break. Young trees and newly planted shrubs can be more vulnerable than large, established trees because damage is concentrated on smaller limbs.
In areas expecting a major emergence, gardeners can consider protecting small or recently planted trees with suitable fine netting during the adult egg-laying period. The net must be fitted so insects cannot get underneath, and it should not be left on indefinitely; follow local horticultural guidance for timing and safe use. Avoid applying pesticides simply because cicadas are noisy or numerous. They are a temporary native emergence, and unnecessary pesticide use can affect other insects and wildlife.
For a damaged branch, ordinary observation is often enough. Some affected tips may wilt or break, but a healthy established tree commonly produces new growth. If a tree has extensive damage or is already stressed, ask a local arborist or extension professional to assess it rather than assuming every symptom is caused by cicadas.
Common misconceptions and practical observations
Several widespread claims blur important distinctions. First, cicadas are not locusts: locusts are grasshoppers, while cicadas are true bugs. Second, cicadas do not sing by rubbing their legs together; male cicadas produce their characteristic calls using specialized structures on the abdomen. Third, their loudness does not mean they are attacking people. Their calls are part of mating behavior.
Another common mistake is treating an emergence as an exact, universal calendar appointment. Brood schedules are geographically specific, and individual emergence can be uneven. A few cicadas appearing before the main wave do not prove that a seven-year cycle exists. Nor does seeing adults in one summer show that the same individual insect lived aboveground for years; the long wait happens mostly underground.
If you want to observe cicadas, look for adults on tree trunks and vegetation, and for the pale, hollow-looking skins left behind after they molt. Listen from a comfortable distance, and do not handle wildlife unnecessarily. If you photograph an insect for identification, include a clear view and note the location and season; those details can be more useful than a guess based on sound alone.
Frequently Asked Questions
Are there cicadas that come out every seven years?
Seven years is not the standard cycle associated with North America’s famous periodical cicadas. The best-known periodical species have thirteen-year or seventeen-year cycles. A report of cicadas after seven years may refer to a local observation, a different insect, or a misunderstanding of brood timing.
What insect comes out every thirteen or seventeen years?
Periodical cicadas are the insects known for these long, synchronized cycles. Their nymphs live underground for most of the cycle, then emerge as adults in large numbers in particular regions.
Do cicadas really stay underground for years?
Yes. Cicada nymphs live belowground and feed from plant roots while developing. The conspicuous winged adult stage is relatively short; it is not the stage that lasts for most of the insect’s life.
Do cicadas come out every year?
Many places have adult cicadas each summer because annual species, or overlapping generations, emerge in different years. That does not mean every individual cicada has a one-year life cycle. Periodical cicadas, by contrast, emerge in synchronized regional broods on longer schedules.
Are periodical cicadas harmful to people or trees?
They do not generally threaten people, and established trees usually tolerate an emergence. Egg laying can injure small branches, so young trees may need protection where cicadas are abundant. Check local horticultural guidance for appropriate steps.
The short answer
When someone asks about insects that come out every seven years, the likely subject is periodical cicadas—but the familiar North American cycles are usually thirteen or seventeen years, not seven. Their long underground development, synchronized adult emergence, regional broods, and brief reproductive period explain both the spectacle and the confusion. For a specific place, local emergence information is the best way to tell which cicadas are expected.