The persistent, loud buzzing or chirping sounds emanating from trees during warmer months are a common experience. These distinct sounds signal the presence of various insects, prompting curiosity about the creatures responsible and how they produce such remarkable volumes.
The Cicada
Cicadas are among the most recognized and loudest insects responsible for tree sounds. These insects typically have stout bodies, prominent eyes set wide apart, short antennae, and two pairs of clear, membranous wings often longer than their abdomen. Adult cicadas usually measure between 2 to 5 centimeters (0.8 to 2 inches), though some species, like the empress cicada, can reach about 7 centimeters (2.8 inches) with an 18–20 centimeter (7–8 inch) wingspan. Over 3,000 described species are found globally in temperate to tropical climates, including deserts, grasslands, and forests.
There are two categories of cicadas: annual and periodical. Annual cicadas, sometimes called “dog-day cicadas,” emerge every year, though their individual life cycles as underground nymphs range from 2 to 5 years. Periodical cicadas, in contrast, are known for synchronized mass emergences every 13 or 17 years, depending on the species and region. Their long life cycles are spent primarily underground as nymphs, feeding on tree root sap, before emerging in large numbers.
The Mechanics of Their Song
Male cicadas are the primary sound producers, creating their characteristic calls using specialized organs called tymbals. These drum-like membranes are located on the sides of the abdomen. The cicada rapidly flexes muscles attached to the tymbals, causing them to buckle and unbuckle, producing a series of rapid clicks. These clicks occur hundreds of times per second, merging into the continuous buzzing or whirring sound we hear.
The cicada’s hollow abdomen acts as a resonating chamber, amplifying the sound produced by the tymbals. This allows some cicada species to generate sounds exceeding 100 decibels, audible over a mile away. The primary purpose of these loud calls is to attract mates, with each species having a distinct song that females recognize. Cicadas also produce different calls, including calling songs, courtship songs, and alarm or distress calls when threatened.
Other Noisemakers
While cicadas are often the most prominent, other insects also contribute to tree sounds. Katydids, close relatives of grasshoppers and crickets, are common nocturnal noisemakers. They produce sounds through stridulation, rubbing specialized body parts together. Katydids rub a sharp edge on their right front wing against a file-like ridge on their left wing.
Crickets also use stridulation to produce their characteristic chirps, by rubbing a scraper on one front wing against a file-like ridge on the other. This action creates a series of sound pulses. While both katydids and crickets use wing-on-wing friction, their sounds differ from cicadas, which use tymbals. Katydid sounds are often described as chirps or buzzes, while crickets produce distinct chirps, heard more frequently at night.
Seasonal Serenades: When and Where to Listen
The loud serenades of these insects are seasonal, primarily associated with warmer months. Cicada sounds are most prevalent during summer, often peaking from July through September in many regions. Their vocal activity intensifies during the hottest parts of the day, from late morning to late afternoon, as their metabolism and sound production are influenced by temperature. Some species have specific singing times, like the Northern Dusk-Singing Cicada, which sings around sunset, or Morning Cicadas, active before noon.
Cicadas are found across all continents except Antarctica, inhabiting diverse environments. In North America, they are widespread, particularly in the southern and eastern United States. Environmental factors, such as soil temperature, play a role in their emergence; many periodical cicadas require soil temperatures around 18°C (64°F) at an 8-inch depth to emerge. Cooler temperatures can silence them, while warmer conditions encourage activity.
Katydids and crickets, while present during the day, are often more noticeably heard at night when ambient noise levels are lower. Their chirping season generally begins in late July and continues into autumn until frosts occur.