by Michele S. Byers, executive director of the New Jersey Conservation Foundation
Fall is coming, and with it the spectacular colors of turning leaves! But it’s not here yet, and don’t be fooled by the curled, dead leaves on the tips of many tree branches.
These leaves are actually souvenirs of this past summer’s visit by periodical cicadas (Magicicada septemdecimum), those mysterious red-eyed insects whose deafening chorus filled many wooded areas of this state we’re in for weeks.
Depending on where you live, you may have witnessed the amazing sight of thousands of cicadas from “Brood II” emerging from holes in the ground for the final phase of their 17-year life cycle. After crawling up tree trunks, shedding their last nymphal skin to become adults, and allowing their new wings to harden, the cicadas spent four to six weeks buzzing around on a crazed mating spree. The sound was as loud as a chainsaw in some northern New Jersey neighborhoods!
Clusters of brown, withered leaves on tree branches are evidence that the cicadas’ mating went well and they successfully created the next generation. And if you’re wondering why the leaves died, here’s why:
After mating, female cicadas cut tiny grooves in the slender tips of tree branches and deposit their eggs inside. Up to 25 eggs are laid in each slit – as many as 600 eggs for each female. Some branches are cross-hatched with hundreds of slits.
The eggs hatch out in a few weeks and tiny cicadas the size of a grain of rice, called nymphs, emerge and drop from the trees. They burrow deep into the ground among tree roots. There they will live for the next 17 years on sap from the roots until they emerge again in 2030.
And although many small branches were killed by the periodical cicadas – a process officially known as “flagging” – no lasting harm will be done to the trees and bushes. Think of it as cicada pruning! While oaks reveal extensive flagging, not all trees experience the dieback. For example, tulip poplars at the Bamboo Brook Outdoor Education Center in Chester had thousands of eggs laid in their shoots, but remained green all summer.
Brood II won’t appear again until 2030, but other broods will emerge before then. All told, there are 12 groups of Magicicada with 17-year life cycles, and three groups with 13-year life cycles. The broods rarely overlap geographically. The next time periodical cicadas reappear in New Jersey will be 2021, when Brood X (last seen in 2004) emerges.
Although periodical cicadas get all the attention, they’re actually the least common cicadas in the Garden State. Annual cicadas are everywhere right now, in the waning days of summer, and the woods are buzzing with their pulsing song!
Cicadas sing best in the heat of the day, but other summer bugs serenade at night. During the warm nights of summer and early fall, you can hear crickets chirping and the wonderfully rhythmic song of many katydid species, a native grasshopper that gets its name from the sound it makes.
One species of katydid buzzes out the syllables “ka-ty-did” or “ka-ty-did-n’t.” The song’s tempo corresponds with temperature; on hot nights the insects sing at a quick pace, while on cool nights they barely croak out the syllables.
As summer turns into fall, enjoy nature’s free concerts while they last!
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