Cicada with a 17-year Itch

Periodic cicada

‘Have your cicada’s broken ground yet?’ I need to tell people that our last big bug year was 2013. Brood X is now emerging in north-eastern and mid-western states but the nearest to us in Tidewater is northern Virginia. Frustrated I don’t have a report this time, I am republishing a post from eight years ago:

Back in 1996, Bill Clinton was still in his first term of office, Charles and Diana agreed to divorce, the Unabomber was apprehended, and Ella Fitzgerald died. That year I hadn’t yet dreamt of moving permanently to North America: I was living in Yorkshire where mad cow disease seized the headlines. While so much history has flowed since, Brood II cicadas were all the while sucking tree roots in secret while waiting for the calendar to flip over to 2013.

I first encountered the brood a couple of weeks ago at a rest area on the I-64 west of Richmond. The first thing travelers noticed after stepping out of their cars was a chirping racket from every direction. I had heard them once before when a 13-year brood of cicadas emerged near home in 2011. This year it is the turn of the 17-year ensemble to sing.

For a few weeks every 17 (or 13) years local residents have sleepless nights. The noise can be as loud as a passing truck, and 90 decibels is a level the Occupational and Safety Administration warns against exposure for more than 8 hours a day to avoid hearing damage. Not being respecters of regulations, male cicadas chirp round the clock.

They are among the great wonders of the insect world, but not just because they have one of the longest life cycles. A question that intrigues me is how they manage to coordinate mass emergence. When ground temperatures rise above 64 °F (18 °C) in the Year of the Brood, the fossorial nymphs start to burrow upwards, breaking the surface first at the southern edge of their range (North Carolina) and progressively towards northern limits (Connecticut).  Soon there are incalculable billions above ground, more than a million per acre, but during intervening years you are unlikely to see any (except perennial species).  So precise is their timing that local residents can plan when to be away on vacation in 2030 for the next big pulse.

They look scary and are the biggest of their kind at an inch-and-a-half long. Their eyes bulge red and wings and legs are striped orange. Through transparent wings you can see a black cigar-shaped body. A bug in a zoot suit, they have a marvelous name, Magicicada septendecim.

I was a member of a naturalist group heading to a wildlife center in the Blue Ridge, but the cicadas in the car park were the most memorable sight of the day. Believed to be a bad omen, superstitious colonists wrongly assumed they were the same as locusts in the Bible that predicted in the Book of Revelation: “Then from the smoke came locusts on the earth …” I guess that every 17 or 13 years there were fiery sermons from the pulpit about the seven last plagues of Armageddon.

For all their fearsome appearance, they are harmless, neither biting nor stinging, and don’t munch vegetation like true locusts. They cause minor tree damage from “flagging” (browning) during nest-building, but are otherwise rather beneficial. Soon after mating and egg-laying the adults die, providing food for critters and fertilizing the soil. Afterwards, the only remaining cicadas are immature “instar larvae”. These nymphs fall out of the tree canopy and those that avoid predation burrow underground to find a juicy root to suck on … and on … and on until the calendar turns.

For the most part, the distribution of broods doesn’t overlap, although they evolved from a common stock a few million years ago.  Today there are 15 broods in North America, twelve with 17-year cycles and three with 13-year, and you won’t find them anywhere else. Of the 3,000 species of cicada worldwide, only seven have periodic behavior.

We watched hordes lumbering up tree trunks and walls; saw many flying unsteadily like old flying boats, often crashing into branches or to the ground where robins pounced. For a small bird, a cicada is hamburger-sized (and just as nutritious), so the diners were soon sated. Everywhere across the hard-trodden ground there were holes, about ten to the square yard and a little larger than from earthworms. These were burrows from which they recently emerged, and scattered nearby were transparent brown shells (exuvia) which they had worn for years underground.

A spectacle I may never see or hear again.