Thu. Dec 7th, 2023
What is that loud humming noise coming from high in the trees?

Today’s post comes to us from the Discovery Program staff at Charleston Lake Provincial Park.

Most summer visitors to the park will no doubt hear a loud humming sound broadcast from high in the trees. The sound starts out soft and gets louder, before decreasing. Some people say it sounds like the whirring of a power saw, with each burst lasting about 15 seconds.

That distinctive “buzz” comes from the canine cicada, a type of insect that is a little smaller than a typical house key (about 3 to 4 cm long). Only adult male cicadas sing, for the purpose of trying to attract a female (in the same way that male songbirds sing). The cicada’s distinctive call is typically heard from mid-July to early fall, and is particularly noticeable on hot days. Cicadas like to sing with the sun: you will only hear them during the day. Not familiar with their unique sound? You can find recordings of their buzzing online by searching ‘Dog Day Cicada Sound’ on any device that allows audio playback.

An adult cicada on a large green leaf.Top view of an adult cicada

How is a cicada similar to a saw?

Have you ever wobbled a hand saw blade or piece of sheet metal? When a hand saw blade or sheet of metal is wobbled, the flat surface distorts and then regains its shape. This movement produces a loud sound. Obviously, a male cicada does not use a piece of metal. But by using its muscles, the cicada wobbles a special membrane inside its abdomen. The sound is then amplified in the abdomen, which is a hollow and largely empty chamber (a sort of megaphone), producing the loud, distinctive hum we hear.

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That call is one of the quintessential sounds of summer. In fact, that’s how this cicada got its name! The term “dog day” refers to the fact that this cicada sings most actively during the hot, muggy “dog days of summer” (named for the time of year when Sirius, the ‘dog star’ of the constellation Canis Majorthe Big Dog, stands out in the night sky).

Although commonly heard, adult cicadas are infrequently seen. This is because they are well camouflaged and usually perch high in trees. But there is a time when you’re more likely to see one (or at least part of one).

From the underground to the treetops

Canine cicadas live several years and have an almost dual life. A female will insert her eggs into tree twigs, using a specialized sharp tube-shaped organ called an “ovipositor” located at the end of her body. The eggs hatch into small nymphs that then fall from the trees to the ground and burrow to the roots of the trees. There they grow underground and feed on the sap from the roots of trees until it is time to molt into their adult form.

The nymph will take several years to develop. Once ready to molt, the sturdy, wingless nymphs will burrow to the surface with their strong, digging forelimbs and climb up a tree trunk. There they undergo a dramatic transformation, as they split longitudinally along their back, emerging as the winged adult (sounds like a science fiction movie?).

Brown shed skin of a cicada nymph on a tree trunkMolted skin of a cicada nymph, found on a tree trunk

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A careful observer may find these nymph skins shed on tree trunks upon closer inspection. These skins are the most notable sign of a cicada’s presence that you will find. see.

Adults fly into trees where they feed on the sap of twigs (inserting their piercing and sucking mouthparts into the bark). Adults only live about a month.

A hand holding an adult cicada.Closeup of an adult dog day cicada

A few adult canine cicadas will emerge each year. Unlike the various famous “periodical cicadas” that only emerge every 13 to 17 years (and are not found in our area, but in parts of the United States and some places in southwestern Ontario), adult daily cicadas Dogs do not all emerge in the same year and have a synchronized life cycle.

The height of summer

Hearing an adult male cicada means summer is upon us – hooray! While cicadas are common in many provincial parks, they can also be found in urban areas, in city parks and forests. Let us enjoy the warmth of summer, greeted by the distinctive call of our warm climate, neighboring the treetops.