Forests across southeastern Massachusetts are beginning to experience a rare event: the emergence of periodical cicadas. Cicadas themselves aren’t uncommon insects. It’s their lifestyle that is unusual. These bugs spend years underground as larvae, slowly feeding on the roots of plants. When they mature, they burrow to the surface and climb whatever is nearby in order to molt into winged adults, a process that takes almost a week to complete. They only live for a few more weeks, flying and loudly calling in search of a mate. Mythologies from all around the world feature the cicadas’ striking songs and legendary longevity.
There are thousands of species of cicada globally, and around 170 in the United States. The vast majority of these are “annual” cicadas, which emerge every year in small numbers. The dog-day cicada, for example, is well known for its piercing cry on hot, still summer days. Between two and eight years old, these are still relatively old for insects, most of which only live for a few days to a couple of years. What we are about to witness are the periodical cicadas, all of which belong to the genus Magicicada, which only live in temperate eastern North America. Brood XIV is here.
There are only seven species in this genus, and they are further organized into fifteen additional groups called broods, based on their year of emergence. Surprisingly, broods can contain multiple different species, all synchronized together to increase their numbers. Each brood follows its own 13 or 17-year cycle, and can have distant, unconnected populations. This year’s emergence, Brood XIV, is also happening in Long Island, parts of Pennsylvania, and across Appalachia. First written about by Governor Bradford in 1634, it last happened in 2008. Of course, people have known them for much longer; stories from Native peoples, such as the Onondaga and the Hopi, tell of cicadas as bringers of bounty and connect them to the origins of mankind and agriculture.
These larvae develop for an astonishing 13 or 17 years, making them among the longest-lived of insects and the oldest in North America. Most cicada predators live shorter lives; they don’t expect the emergence and may be slow to try a strange new food. The long gap between generations prevents other animals from evolving alongside them into specialist predators. Mathematical models suggest that the intervals between prime numbers may be significant. If they had 16-year cyc
les, for example, predators with 1-, 2-, 4-, or 8-year population cycles would eventually overlap and eat a large number of cicadas. The exact mechanism that governs this miraculous coordination is still unknown to science, but it is believed they have a sort of molecular clock that tracks the yearly cycles of plants they feed on. Oddly enough, the larvae all mature at different speeds, yet almost every one is ready the correct year, with only a few missing the target by a year or two.
Cicadas emerge in mind-blowing numbers. Up to 1.5 million cicadas per acre have been documented . The sheer quantity of them overwhelms predator populations, a strategy known as “predator satiation”. It also makes it easier to find a mate, in a sense. Cicadas don’t have to travel far to find another cicada, which is good because they are clumsy in flight. However, since there are so many to choose from, and multiple species, males try to attract attention to themselves by screaming. They accomplish this with two organs called tymbals, comprising a vibrating muscle in a resonant drum. The females, however, are pretty quiet, only making soft clicking noises to communicate with their mates.
Hundreds of cicadas that have emerged hang on the branches of a maple tree.
The colonial accounts often described them as locusts, which is a voracious type of grasshopper. Cicadas, despite the drama, swarm to mate, not to eat. The females carve small channels in the branches for their eggs, which can damage the
branch tips. While they do feed from tree branches, they don’t do much more than prune the tips, which can actually be of benefit to the forest. Despite their size, they are essentially harmless and don’t bite defensively. If you are very still, however, they may confuse you for a tree and poke you. When the eggs hatch later this summer, the larvae drop from the canopy and quickly burrow underground. This stage may be a little awkward for hikers, but they are also harmless.
Brood XIV is the only periodical cicada emergence in our area since Brood XI went extinct in the 1950s. Wareham, sadly, will mostly miss out on this experience, as the emergence is primarily on the Upper Cape and in some areas of Plymouth. A truly extraordinary event, it’s well worth the short travel and 17-year wait.
By Justin Cifello
Wareham Land Trust Member and Volunteer