As the weather heats up, Canadians are likely to start hearing cicadas, the winged insects whose shrill mating call is one of the signature sounds of summer in North America.

While cicadas crop up in various parts of the continent each summer, the northeastern U.S. is experiencing a massive emergence this year of what is known as "Brood II." These cicadas are part of a subspecies called Magicicada, and have been living underground for 17 years.

Here are some interesting facts about cicadas.

What does the word "cicada" mean?

"Cicada" comes from the Latin, meaning "tree cricket." While cicadas are often colloquially referred to as a kind of locust, they are not part of the locust family.

How many species are there?

There are about 3,000 known species of cicada worldwide, according to the Smithsonian Natural Museum of History. 

There are annual cicadas, which appear every year, and periodical cicadas, such as the ones emerging in the northeast U.S., which appear in 13- and 17-year life cycles. Periodical cicadas are only found in eastern North America.

What do they eat?

For the most part, cicadas subsist on the fluids of living trees.

What are their predators?

Take your pick: birds, small mammals, spiders and other insects, such as ants.

What happens in the 13 or 17 years that periodical cicadas live underground?

The 13- or 17-year life cycle of a periodical cicada begins when an adult female cicada drops her egg in the soil. The growing cicada then spends the next 13 to 17 years as a "nymph," or juvenile, a period that contains five distinct phases.

Juvenile cicadas live at depths of 30 centimetres or more and subsist on the juices of plant roots until the final year. When the soil temperature reaches about 18 degrees Celsius, they burrow their way to the surface. They then climb a tree, where they shed their nymphal skin and emerge as adults.

How long do the adults live?

Once they rise from the soil, these cicadas live for four to six weeks. Their time above ground is spent mating and avoiding predators.  

How significant will this year’s cicada population be?

According to Magicicada.org, the population density of periodical cicadas could range from tens of thousands to as high as 1.5 million insects per acre this year (or about 3.7 million per hectare).

Why do periodical cicadas have 13- and 17-year life cycles?

Researchers and cicada enthusiasts have noted that the life cycles of periodical cicadas are prime numbers, i.e. the figure can’t be evenly divided into smaller integers.

There is no reliable explanation for this, but in a recent blog post, the New Yorker magazine cited well-known paleontologist Stephen J. Gould, who suggested that the life cycles of periodical cicadas are an evolutionary survival strategy.

U.S. cicada expert John Cooley points out on Magicicada.org that because periodical cicadas emerge in such staggering numbers, there are enough cicadas to satisfy its predators, while also leaving plenty of insects to mate and continue to propagate the species.

Another theory for their long gestation is that it’s a holdover from an earlier period of history, when the earth was cooler, and cicadas that learned to live underground longer would be less likely to die in an unexpectedly cool spring.

Just how loud are cicadas?

Cicadas are among the loudest insects known to man, and a swarm of them can produce sounds up to 120 decibels. That's louder than a rock concert (about 115 decibels), and comparable to the noise from a chainsaw (humans start to experience pain from sound at the 110 to 120 decibel level).

Are they attracted to other summer sounds, like lawnmowers?

According to Cicadamania.com, cicadas will gravitate to other noisy summer objects, like lawnmowers, because female cicadas mistake them for singing males, and male cicadas will follow in order to continue wooing the females.

Sources: Magicicada.org, Cicadamania.com, Smithsonian National Museum of Natural History, Purdue University.

Corrections

  • This story originally contained two errors. The first incorrectly converted the estimated number of 17-year cicadas in an acre to the estimated number in a hectare. The second mistakenly referred to xylem as tree fluid, rather than plant tissue that conducts fluid.
    Jun 17, 1970 9:41 AM ET