I don’t live in the country, so it was somewhat surprising when, around June, I heard the pulsing melody reminiscent of a meadow on a summer evening—a cricket chirping. I first noticed a sole chirper, who I unceremoniously named Jiminy, and whose rhythmic whistle I listened for every night. I worried about him, as his constant and lone chirp made me think he would be forever without mate, a sad, lonely cricket in a backyard. But by August, he had friends—lots of them, by the sounds of it. They begin their symphony around dusk and continue well into the night, stopping only when a human or another perceived threat approaches.
The sound of crickets is for most people a soothing and welcoming reminder of summertime; Nathaniel Hawthorne once wrote of the chirping: “If moonlight could be heard, it would sound just like that.” Yet why and how do these insects produce their lovely sound? And can you really predict the outside temperature based on a cricket’s chirp, as folklore says?
A Cricket by Any Other Name
It’s no surprise that I have crickets in my yard; they like to live under rocks, among ground litter, under leaves, and in meadows. While a cricket in the house can be a nuisance, in the yard, they’re for the most part beneficial, helping to break down plant materials and add nutrients to the soil.
Crickets are of the insect order Orthoptera, which also includes grasshoppers and katydids. Often confused with grasshoppers due to their similar body shape and large hind jumping legs, grasshoppers are more of a nuisance, as they can destroy crops and denude entire trees.
Grasshoppers are usually green, while crickets are brown to black (tree crickets are all green) and they have wings that may cover half to the entire abdomen.
The wings on a cricket are what they use to make sound, and this pulsing song is critical to a male’s reproductive success. One wing has a ridge called a scraper and the other has a set of ridges called the file. When rubbed together, it produces a sound; this action is known as stidulation.
The males make their sound to attract females, so it’s important she can hear it. On a cricket’s leg is a tightly stretched membrane, called a tympanum, which functions like an ear. By turning toward the sound, crickets can tell which direction it’s coming from. Females pick the male with the nicest song and head toward him.
But not all chirps function to lure in a lady. In addition to the loud mate attracting and competitive male repelling sound, crickets produce a quiet courting song when a female is near. A different chirp is made when two competing males encounter each other and another is made to warn other crickets of danger.
The sound is a product of the wing shape and each species of cricket has its own specific sound. One of the coolest things about having a lot of crickets around is hearing the males start to chirp in synchronicity. Like the choreographed flashing of fireflies, the in-unison cricket sound isn’t completely understood. It’s hypothesized to either function in cooperation—helping to minimize the threat of predators, for instance—or as a competitive tact, helping some males gain advantage over others, due to the muddled message of individuals insects.
We usually hear crickets during late summer and autumn because this is when they need to mate and reproduce. In cold climates, adults die during the winter, so they need to ensure that they find a mate while it’s still warm. After mating, females deposit their fertilized eggs in the ground or other suitable repository with a long tube-like apparatus called an ovipositor (easy to remember: egg + depositor) for a spring hatch.
Because a cricket’s sound is dependant on the weather, it’s been said that one can tell the outside temperature based on the frequency of chirps. Like all insects, crickets are cold-blooded and their activity levels depend on temperature. Both metabolism and chirping will vary with ambient temperature; in warmer weather, chirping will be faster, in colder weather, it’s slower. A formula, called Dolbear’s Law, states that you can approximate the outside temperature in degrees Fahrenheit by counting the number of chirps in a fifteen second span and adding forty. Although chirping varies from species to species, and therefore this formula doesn’t work for all crickets, it does hold pretty much true for the snowy tree cricket species. Scientists have modified the formula slightly, counting the chirps of the tree cricket every thirteen seconds in the eastern U.S. Of course, it can be difficult to determine what kind of cricket lurks in your lavender, so a thermometer is probably a much safer bet.
I’m no longer able to make out Jiminy’s sound amidst the cacophony of other guys out in the flowers, but I don’t mind. I hope his trailblazing sound helped him find a perfect mate.
The Bugs of Summer is a special series bringing you the lowdown on the flying, crawling, and sometimes stinging insects that roam our skies during the warm months. Whether they delight or annoy, we’ll give you the scoop on how to appreciate or avoid our six-legged friends. Read the previous article here.
Updated July 19, 2010