I wanted today’s post to coincide with the arrival of some long- (as in 17 years!) anticipated garden guests. Unfortunately (unless you planted baby fruit trees this spring), they have yet to show.
The delayed guests, aka the “Great Eastern Brood” or simply “Brood X,” are trillions of 17-year periodical cicadas expected to emerge from underground across the mid-Atlantic, southeastern, and Midwestern United States. (Yellow areas of U.S. Forest Service chart)
The evening air of Evansville, IN, should already resound with Brood X’s overpowering buzz. But according to the Evansville Courier & Journal, their cacophony is two weeks overdue.
Since the first record of their appearance in 1715 Philadelphia, the 17-year emergence of Brood X has gone almost like clockwork. That is, until 2017!
What happened then to change an eons-long pattern of behavior? Over much of their territory, swarms of Brood X cicadas crawled from their underground chambers four years ahead of schedule!
Scientific American reported sightings of the prematurely arriving insects in:
- Washington DC
- North Carolina
In other words, billions of Brood X periodical cicadas miscalculated and took flight far too soon. However, billions more that remained underground have now fallen behind schedule.
But why? The answer lies in…
The Underground Life of Periodical Cicadas
Of the more than 3,400 cicada species, only seven (1/5 of 1 percent) qualify as periodicals. Four of those species emerge every 13 years. The other three, including Brood X, have a 17-year underground residency.
How did they get there, and what do they do all that time?
As juveniles or nymphs, the cicadas burrow down through the soil to a depth of 7 or 8 inches and survive on root fluids. According to the University of Connecticut, they pass through five developmental stages before reaching adulthood.
In the spring of their 17th year, the nymphs start constructing exit tunnels to the surface. What triggers this activity remains a mystery, but when the soil at burrow level reaches 64 degrees Fahrenheit, they emerge en masse.
The exodus usually occurs after sunset on a dry, windless night. The nymphs then head for the nearest suitable vegetation to molt. After another four to six days, when their new exoskeletons have hardened completely, they find trees to begin carrying out their mating ritual with its accompanying 100-decibel serenade.
So why, after following this developmental sequence for about 5 million years, has Brood X decided to switch things up by being early and then late to the party?
Could they be telling us something?
Periodical Cicadas as an Indicator Species
Over the course of 5 million years, all cicadas have had to adapt to multiple climatic and environmental changes. Brood X has inherited those survival traits.
But are they enough to let the insects cope with what’s happened to their world over the last century?
Scientific researchers consider these cicadas an”indicator species,” according to Purdue Univerity forest pest educator Elizabeth Barnes.
This makes them vulnerable to even slight environmental changes that most other species may recover from. Loss of habitat and deforestation for real estate development and farming is robbing them of the trees they rely on for food, mating, and egg-laying.
Lengthening winters and hotter summers may disrupt the internal clocks that tell them when it’s time to emerge. Every paved-over acre of soil can mean up to 1.5 million periodical cicadas will never again see the light of day.
But unlike most species threatened with the loss of their natural environments, Brood X gets only one shot every 17 years to continue their species. If the number of them emerging continues to decline, spiders, birds, wasps, beetles, and other predators will eventually finish what human activity has started.
When I first considered writing an article about these fascinating creatures, the plan was to explain how to protect young fruit trees from becoming their nurseries. But the more I read, the clearer it became that it’s the insects, and not the trees, in need of our help!