Summer’s arrival often brings with it a distinctive soundscape, punctuated by the sometimes overwhelming chorus of cicadas. Depending on your location, these insects can be a subtle background hum or an inescapable wall of noise. But Why Are Cicadas So Loud? Let’s dive into the fascinating world of these buzzing bugs to understand the science behind their signature sound.
Cicadas, scientifically classified within the insect order Hemiptera, are relatives of aphids and leafhoppers, not locusts as they are sometimes mistakenly called. Globally, over 3,000 different species of cicadas exist, each with unique characteristics. They are characterized by their stout bodies, short antennae, widely spaced eyes, and two pairs of wings that are typically transparent in adult specimens. Remarkably, cicadas spend the vast majority of their lives underground as nymphs, emerging only briefly as adults for a few weeks to reproduce before they die.
While the term “locust” is often used interchangeably with cicada, especially when describing large emergences, it’s important to distinguish between the two. Locusts are actually grasshoppers and are not closely related to cicadas. Locust swarms and cicada emergences occur for different biological reasons.
Annual vs. Periodical Cicadas: Understanding the Life Cycle
Most cicada species are considered “annual,” meaning that adults from different generations emerge every year. However, even annual cicadas live underground for multiple years in their nymph stage.
Periodical cicadas, primarily belonging to the genus Magicicada, exhibit a truly unique life cycle. These species emerge synchronously in massive numbers after long periods spent underground, either 13 or 17 years, depending on the species. This synchronized emergence is a rare phenomenon in the animal kingdom, with only nine known species of periodical cicadas and one species of periodical millipede identified so far. These periodical cicadas are exclusive to North America, with four species on a 13-year cycle and three on a 17-year cycle.
Broods and the Mystery of Numbers
Within a specific geographical area, different species of periodical cicadas sharing the same life cycle year will emerge together. These groups are known as “broods,” identified by Roman numerals. It’s crucial to understand that these brood numbers are simply identifiers and do not carry any special biological significance.
In 2024, for example, Brood XIX, a 13-year brood, is emerging across a significant portion of the United States. This brood encompasses all four 13-year periodical cicada species, although other broods may have different species compositions.
The mass emergence of periodical cicadas is a predator avoidance strategy, albeit a peculiar one. Individual cicadas are vulnerable with limited defenses. Predators like birds, wasps, and squirrels capitalize on this abundant food source. However, the sheer volume of cicadas overwhelms predator populations. This “predator satiation” strategy ensures that enough cicadas survive to mate and reproduce, continuing the cycle.
The summer of 2024 is particularly noteworthy due to the simultaneous emergence of two distinct broods: Brood XIX (13-year) and Brood XIII (17-year). This rare double emergence is predicted to unleash approximately one trillion cicadas across 16 states, a spectacle that occurs only once every 221 years.
Emergence and Life Above Ground
Cicadas begin their emergence when the soil temperature reaches approximately 64 degrees Fahrenheit at a depth of six inches. They climb trees or other vertical surfaces to undergo their final molt, transforming into winged adults.
Adult cicadas have a short lifespan of only a few weeks. During this time, their primary focus is reproduction. Females lay eggs in tree branches before dying. Once hatched, the nymph cicadas drop to the ground and burrow to begin their underground life cycle.
While underground, cicadas track the passage of years by sensing seasonal changes in tree xylem, the watery sap they consume. Whether a cicada follows a 13-year or 17-year cycle is genetically determined.
The Science of Cicada Sound: Why So Loud?
The most prominent characteristic of cicadas is undoubtedly their intense loudness. Despite their relatively small size compared to other loud animals, cicadas are among the loudest creatures in the animal kingdom.
Cicadas possess a unique sound-producing organ called a “tymbal.” This structure, located on their abdomen, buckles and clicks rapidly, creating sound. Male cicadas contract their tymbal muscles hundreds of times per second. This rapid clicking, repeated continuously, merges into the droning, buzzing hum we associate with cicadas.
Male cicadas “sing” to attract females for mating. In many species, males aggregate in large groups, forming choruses that amplify the collective noise to deafening levels. Groups of periodical cicadas can reach sound levels comparable to lawnmowers or leaf blowers, exceeding 100 decibels. While this sound may seem cacophonous to humans, each cicada species has a distinct song, crucial for species recognition and mate attraction. These songs are species-specific, allowing cicadas to identify and attract the correct mates.
Cicada Diet and Habits
Cicadas are xylem feeders, meaning they derive their nutrition solely from the watery xylem sap of trees. They possess a straw-like proboscis, which they use to pierce plant tissue and extract sap. Nymphs feed on tree roots, while adults feed from branches.
Xylem sap is nutritionally poor, requiring cicadas to consume vast quantities to obtain sufficient nutrients. Similar to other animals with low-nutrient diets, cicadas process large volumes of fluid. After extracting sugars and nutrients from the xylem, the remaining water is excreted as liquid waste. This “cicada rain,” often noticed under trees during cicada season, is harmless and a natural consequence of their feeding habits.
Cicadas and Their Impact on the Environment
Cicadas pose no danger to humans or pets. They lack stingers and are incapable of biting defensively. Their clumsy flight may occasionally result in accidental bumps, but they are otherwise benign. While the noise can be intense, it does not pose a hearing risk unless one is in extremely close proximity to a singing cicada.
Pets may be tempted to eat cicadas, which is generally safe in moderation. However, consuming too many cicadas can cause digestive upset due to their exoskeletons. Humans also consume cicadas and have done so historically. Numerous cicada recipes are available for adventurous eaters.
Cicadas are not considered pests and are, in fact, beneficial to ecosystems. Their burrowing activity aerates soil, and their decaying bodies enrich the soil with nutrients upon death, acting as a natural fertilizer.
While cicada egg-laying in young trees can cause minor damage, mature trees are generally unaffected. Protecting young trees with mesh netting is a simple preventative measure. Pesticide use is strongly discouraged as it harms beneficial insects and disrupts the ecosystem.
Instead of viewing cicadas as a nuisance, we should appreciate their unique biology and ecological role. Their loud summer serenade is a natural phenomenon to be experienced and understood.
Embracing the Cicada Summer
To make the most of this loud bug summer:
- Explore resources like Cicadamania.com to deepen your cicada knowledge.
- Utilize the Cicada Safari app or iNaturalist to identify species and contribute to scientific tracking.
- Consider trying cicada recipes for a unique culinary experience.
- Use deceased cicadas as garden fertilizer.
- Find inspiration in this natural spectacle – create art, start a time capsule, or even compose cicada-themed haikus, as inspired by the examples below:
In patience, we wait
To finally sing our song
Please, let it echo on– Staci Cibotti
In soil they slumber
Years pass, they rise in chorus
Respect their journey– Emily May
Cicadas are here
Don’t spray – there’s nothing to fear!
Just enjoy their song– Aaron Anderson
