by Dr. Sarah Treanor Bois, PhD
Director of Research & Conservation at the Linda Loring Nature Foundation
You may have been hearing some buzzzzz about cicadas in our regional news outlets lately. Throughout the state, people are preparing for an onslaught of insects. Why, when, and where?
Well, first the “what”: the emergence of Cicada Brood XIV begins this month and has got many people either bracing for a swarm or looking up cicada recipes. This is one of the few periodic cicada broods known from Massachusetts. But what does that mean for us here on Nantucket? And what even is a “brood” anyway?
Let’s start with cicadas in general. Cicadas are a group of insects related to leafhoppers, treehoppers, spittlebugs, and aphids. There are many different species (9 have been documented in Massachusetts). The most common in our area, the dog-day cicada, emerges every one or two years. But since their emergence isn’t synched with other cicadas, some will emerge every year. Other species are periodic with all individuals synched. All periodical cicadas of the same life cycle type that emerge in a given year are known collectively as a single “brood.” Scientists have identified each brood and designated it with a Roman numeral. They are well-tracked by scientists and cicada enthusiasts who keep watch. The University of Connecticut maintains a brood database for the northeast ( cicadas.uconn.edu/broods ). There is a wealth of historic and present-day information on cicadas in our region.
Each brood has its own unique range, population size, and emergence cycle. There are 15 different periodic broods in North America, two of which occur in New England. The hot topic around here is the emergence of brood XIV. This periodic brood has a 17-year cycle. So the upcoming emergence of brood XIV was last seen in 2008. As of this writing, they have already emerged in Kentucky, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia. Brood XIV is also expected to emerge this spring in Georgia, Indiana, New York, New Jersey, and Massachusetts.
Historical dates for brood XIV in Massachusetts include appearances over the 1700s, 1800s, and 1900s in Barnstable, Dennis, Falmouth, Bourne, Plymouth and a handful of other nearby towns. Brood XIV was recorded in 1624 by Massachusetts Governor Bradford. It may be the only one to occur in Massachusetts.
For Massachusetts, you can check out an iNaturalist Live Map for emergence sitings of Brood XIV. The reports right now are of the emerging nymphs. When the magic year arrives for these cicadas, the nymph digs to the surface, normally during the night, crawls up a tree trunk, and anchors itself with its claws. The skin of the back then splits, and the winged adult emerges and seeks its preferred habitat. While the adults only have a lifespan of three to four weeks above ground, when we notice them the most, the male cicadas make their presence known with buzzing sounds to attract mates. Females then lay eggs in trees, and by the end of the summer, the nymphs will hatch and burrow underground, feeding off roots until they emerge again in 2042.
How do they know when to come out of their burrows? Published literature suggests that periodical cicadas keep track of time by using an internal “counter” that keeps track of annual cycles. When their annual cycle is up, cicadas can gauge the temperature to figure out when to emerge from the soil.
According to cicadamania.com, the brood XIV cicadas emerge when the soil 8 inches beneath the ground surface reaches approximately 64°F. A warm rain will often trigger an emergence.
Unfortunately for us, Brood XIV never makes it out to Nantucket. They typically prefer mesic forested landscapes, of which we have little here. Even the Cape populations are unusual for their sandy soils.
On-island, we primarily have four species of cicadas; the Northern Dog-day Cicada (Neotibicen canicularis), the Swamp Cicada (Neotibicen tibicen), Common Lyric Cicada (Neotibicen lyricen ssp. Lyricen), and the Southern Dusky-winged Cicada (Neotibicen tibicen ssp. Australis). You can see examples of all of these on iNaturalist (www.inaturalist.org).
The most common, dog-days cicadas, got their name because of their loud calls late in the dog-days of summer. When you think of a hot, August day out in the moors of Nantucket, the calling cicadas are the soundtrack you’re hearing. Scientists have found that their song varies in pitch and intensity based on temperature cues. Cicadas like heat and do their most spirited singing during the hotter hours of a summer day in a roughly 24-hour cycle. A cicada’s high-pitched song not only attracts females (and other males who join in the cacophony) but it also repels birds. In some cases the din is enough to throw off avian communication and disrupt their group hunting behavior.
For a species so influenced by temperature, climate change is likely having impacts, especially on cicada emergence patterns, potentially leading to earlier and more unpredictable emergences. Warmer winters and earlier springs could trigger cicadas to emerge before their usual time, or even shorten their typical emergence cycle.
So, should we be worried about these emerging cicadas? Friend or foe? I vote for friend. Cicadas do not kill trees and are around for such a short time that any damage they cause is short-lived. They don’t carry diseases and aren’t harmful to wildlife. In fact, their presence is a boon to anything that will eat them, including many bird species. There is even a predator known as the cicada killer. This big black and yellow parasitic wasp catches and paralyzes cicadas before dragging them down into an underground burrow where it will serve as food for the larva. The only real “harm” cicadas inflict is their sometimes-deafening sound. We hear it over the whole island in summer, but it doesn’t mean cicadas are everywhere. The males are rubbing their legs together calling for females who can be more than a mile away. Thus, the extremely loud sounds as the male cicada tries to let his presence be known.
I like thinking of these newly emerging cicadas like living time-capsules. If only we could interview one about what life was like in 2008. Would they be shocked about what things are like today? Well, they may be disappointed in habitat changes or reduced food availability. Too bad they don’t make it out to the islands where habitat is plentiful. Who knows, a few may make the ferry after all.
