University of Michigan entomologist Thomas Moore was walking in the yard of his Ann Arbor-area home May 24 when he heard the unmistakable droning buzz of a single periodical cicada in the distance.

He knew instantly what it was, down to the exact species, and a thrill shot through him.

“I never tire of hearing that sound,” Moore said. “It’s marvelous, and it’s a thrill every time there is an emergence.”

Moore, 91, has spent nearly seven decades studying periodical cicadas, which emerge every 13 or 17 years and are only found in the eastern half of North America. He logged thousands of miles during his career, crisscrossing the country by car, and studied 55 periodical cicada emergences.

Moore said he began listening for the arrival of the periodical cicada group called Brood X at the beginning of May. Brood X is among the largest groups of 17-year cicadas by geographical extent, with a patchwork distribution that ranges east to Long Island, south to Georgia, west to Illinois and north to southeastern Michigan.

While the fiery-eyed bugs had already emerged in other states after developing underground for 17 years, chilly spring weather delayed their widespread appearance in Michigan. Until May 24.

“At 91, I sometimes wondered if I would get to hear them again this year, and by golly I did,” said Moore, professor emeritus of ecology and evolutionary biology and a curator emeritus at the Museum of Zoology. “But I’m pretty sure this will be the last time I see them.”

When the ground temperature warms to 64 degrees at a depth of 8 inches, juvenile periodical cicadas emerge from holes in the ground and crawl up a tree or shrub until they are several feet above the ground. Then they grasp the bark with their claws and shed their juvenile exoskeleton in a process called molting, leaving behind a papery brown shell.

Newly emerged adults will cling to those shells for a day or two as their wings unfold, their muscles finish developing, and their skeletons harden and darken, Moore said. The Brood X cicadas are members of the genus Magicicada and have striking black bodies, bulging red-orange eyes and red wing veins.

Adults are about an inch long and live for about a month, during which time “they sing, mate, lay eggs, sing a little more, and then they die,” Moore said. Adult males gather and sing in dense aggregations called choruses, said Moore, who specialized in cicada sound production and perception.

“The males are calling females to them, and they are saying, ‘I’m here, I’m ready to mate, and you’re my kind,'” he said.

Moore said the cicada he heard May 24 was from the species Magicicada septendecim.

Female periodical cicadas insert eggs into slender tree stems through a needle-like tube called an ovipositor. Both male and female adults also suck sap from woody plants through their mouth parts. Those activities can cause localized damage to trees and shrubs, but “normally plants have no problem recovering from it,” Moore said.

Overall, periodical cicadas have a positive effect on forests because their emergence holes allow sunlight, oxygen and rainwater into the soil. The adults provide a food bonanza to all sorts of wildlife, from birds and squirrels to skunks and raccoons — even domesticated dogs and cats eat them. And when the adults die and decompose, rainwater washes nutrients into the soil.

When the newly laid eggs hatch, the hatchlings crawl or drop to the ground and begin to dig with their front legs, not to be seen again for 17 years.

“I’ve seen periodical cicadas emerge 55 times, but I’m still enthused whenever it happens,” Moore said. “It’s always good to hear a cicada sing.”

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