15 Baffling Cicada Facts

Cicadas are a superfamily of winged insects that live mostly underground and emerge at intervals of one, 13, or 17 years. There are over 3,000 species living around the world, but the most well-studied are those belonging to the genus Magicicada, which includes seven species of periodical cicadas common in eastern North America.

The long-lived arthropods are stout, green or brown in color, with red eyes and transparent wings. They're known for their deafening songs and the golden skins they cast on trees. That some species are at risk of extinction due to climate change makes cicada education and conservation increasingly important.

Here are 15 facts about these sporadic anomalies of the bug world.

1. Cicadas Live on All Continents Except Antarctica

The superfamily Cicadoldea is split into two subfamilies: Tettigarctidae (aka hairy cicadas), which are mostly extinct save two extant species that occur in southern Australia and Tasmania, and Cicadidae, which can be found on every continent except Antarctica. They thrive in warm environments — especially the tropics — which makes Latin America, Australia, Southeast Asia and the Western Pacific, and South Africa hotspots.

There are more than 170 described species throughout the U.S. and Canada, and the U.S. alone is home to 15 "broods" (groups of cicadas with varying life cycles).

2. They're Not Locusts

That cicadas are often called locusts is deceiving, as they hail from the taxonomic order Hemiptera (true bugs) and locusts belong to the order Orthoptera with grasshoppers. A few behavioral and physical attributes could be the culprit of the misnomer. Firstly, cicadas share a suborder with other "hoppers" of the leaf and frog variety, even though they don't hop themselves. Secondly, their tendency to swarm is similar to the locust's. Experts estimate that when the 17-year broods emerge in the U.S., they're as concentrated as 1.5 million cicadas per acre.

One difference, beyond their scientific classifications, is that cicadas pose little to no risk to crops and vegetation, whereas a swarm of locusts can consume the same amount of food as 35,000 people in a single day.

3. They Have One of the Longest Insect Life Spans

An annual cicada can live between two and five years, and a periodical cicada can live for up to 17 years in the larva stage. That's not quite as long as queen termites are thought to live (50 to 100 years), but it's far more impressive than the average life span of a housefly (15 to 30 days). 

Cicadas, like most insects, live the majority of their lives in the immature stages of development. While some can remain underground for more than a decade, they typically die only a few weeks into adulthood.

4. Periodical Cicadas May Be a Result of Ice Ages

A leading hypothesis for why there are both annual and periodical cicadas, and why the life spans of periodical cicadas vary, is that some broods — located east of the Great Plains in the U.S. only — developed extremely long juvenile stages during the glaciated Pleistocene Epoch. That northern broods tend to remain underground for longer than southern broods in the U.S. corroborates this theory. However, critics say it doesn't make sense that glaciation would affect cicada populations of only a certain area when other cicada habitats were covered in ice just the same.

Their tendency to emerge only in prime number cycles is thought to be an effort to prevent predators from feasting on them repeatedly.

5. Most of Their Lives Is Spent Underground

Cicadas hatch above ground, about six to 10 weeks after the eggs are laid in cracks and holes in trees. They promptly drop to the ground and burrow up to a foot into the soil, where they remain for up to 17 years. While they're below ground they molt, rather than pupate, through five instars (growth cycles). 

The most mortality occurs during those early stages of life, when the nymphs compete for feeding space underground. 

6. Swarming Is a Survival Strategy

It's unclear how many cicadas are included in a single brood, but experts estimate that there are billions. Their portly bodies blanket backyard tree trunks. Their collective songs impede outdoor conversation. Cicadas are known swarmers, but their synchronized emergence is actually a deliberate survival strategy called predator satiation. When an animal occurs at such a high-density population, predators quickly become satiated, therefore increasing the chances of survival for a large percentage of young.

7. They Only Emerge When the Ground Is 64 Degrees

The exact moment when cicadas emerge en masse is very calculated. It happens only when the ground eight inches below the surface reaches 64 degrees Fahrenheit — and not one degree higher of lower. When that temperature is finally reached, the nymphs know it's time to begin their upward journey via a chimney of mud. This usually happens soon after sunset, and they will climb high into the trees before most humans have even noticed their arrival. The phenomenon can take place over several evenings.

8. Cicadas Get Their Nutrients From Trees

While underground, cicada larvae aren't hibernating; rather, they spend up to 17 years just feeding on trees. They have special straw-like mouths used to suck liquid from plant roots. What they're really after is xylem, a botanical vascular tissue that helps conduct water and dissolved minerals from the roots. Because xylem tissue is mostly water, cicadas are thought to be malnourished — which could be the reason for their slow maturation.

Molting cicadas that live on small twigs can kill juvenile trees and shrubs, but mature trees welcome the pruning. When the cicadas die, the decomposition of their carcasses also serves as fertilizer.

9. Females Can Lay Up to 600 Eggs

In the few short weeks she spends aboveground, the female cicada lays 400 to 600 eggs. She uses her egg-laying organ, the ovipositor, to make rows of pockets in twigs. She'll then lay about 25 eggs in each pocket, and a single twig can hold up to 20 pockets, sometimes creating what looks like long, parallel slits. Tree species popular for cicada egg laying include hickory, oak, and several fruit-producing trees.

10. Scientists Don't Yet Know How They Tell Time

While experts hypothesize that periodical cicadas only emerge every 13 or 17 years to evade repeat predators, because they're slow to mature, and due to the historical necessity of extended juvenile periods, the insects' time-tracking methods have long remained a mystery. Findings from one study indicated that they may use more than just their biological clocks to tell time so precisely — they could be using the trees.

In the study, researchers transplanted 15-year-old, 17-year cicada nymphs under a tree whose blossoming cycle had been altered to occur twice per season. When a tree blossoms, it produces high sugar and protein levels, detected by the cicadas feeding on their roots. The nymphs emerged a year early in the study, indicating that they keep track of time by counting their host's seasonal cycles.

11. They Can Reach Three Inches in Length

The smallest cicada in North America is the half-inch-long aridland cicada (Beameria venosa), which was discovered in Arkansas. The largest known cicada is Southeast Asia's empress cicada (Megapomponia imperatoria), which can be 3 inches in length and have a wingspan of up to 8 inches. Some cicada species are among the largest true bugs in the world.

Those lengthy bodies house four transparent, veiny wings (including a pair that's longer than the abdomen), two bulging eyes on either side of their heads, three additional eyes on top of the head, and bristly antennae located in front of the eyes.

12. They Abandon Their Skins

By the end of a cicada summer, billions of translucent skins called exuviae will blanket tree trunks even after their hosts have died off. Shedding these skins is the first order of business after emerging from the ground. Once emancipated from their final nymph casing, they must wait for their wings to inflate with fluid and their new skins to harden. Only then can they go about singing and mating through their fast-and-furious period of adulthood.

13. Their Songs Are as Loud as Chainsaws 

Those in cicada-prone areas know to schedule weddings and other outdoor parties around active seasons due to the insects' deafening songs. Only males make this familiar cricket-like noise (hence the name "cicada," meaning "tree cricket" in Latin) — they do it by rubbing their wings together and using a special organ on their exoskeleton called a tymbal, which creates a series of rapid clicks. They produce two sounds: one to attract mates and another to repel predators.

Their songs can reach 120 decibels — which is as loud as a chainsaw and even louder than live rock music — and can be heard up to a mile away. Naturally, a group of cicadas singing is called a chorus.

14. They're Widely Eaten — Even by Humans

Like many big-winged insects, cicadas are clumsy flyers, which makes them easy targets for birds and one of their biggest predators, cicada killer wasps. They are periodic feasts for lizards, snakes, rodents, raccoons, and even fish, cats, and dogs. These ground predators are the reason they race, upon emerging, to get high up in the trees.

But humans also eat them. They're known to boast a sweet flavor, almost like shrimp, and are commonly deep-fried for Shandong cuisine in China. Even people in the U.S. will eat them raw, boiled, grilled, and stuffed.

15. Some Species Are at Risk

The IUCN Red List of Threatened Species lists three cicada species — Magicicada septendecim, Magicicada septendecula, and Magicicada cassini, all endemic to the U.S. — as Near Threatened. Broods XI and XXI have already gone extinct; Brood VII is declining. 

While the IUCN doesn't specify the cause of such population declines, many experts point to climate change. Periodical cicadas are especially sensitive to climate, so as the temperature warms, they've been observed emerging in places where they're not expected or emerging off-cycle. Due to their abnormal behavior, these cicadas have been called "stragglers."

The Midwestern species M. neotredecim is one example of 17-year cicadas permanently switching to a 13-year cycle. In 2017, a number of cicadas from the widespread Brood X emerged four years earlier than expected, too.