Hearing Cicadas? Here's What You Should Know About These Bugs, Their Sounds, and Their Effects on Nashville Trees
What to Know About the 2024 Cicadas
Cicadas in Tennessee 2024
2024 is a special year for the cicada population, as the Eastern United States is experiencing multiple waves of cicada emergences! In addition to the yearly late-summer cicadas, Nashville will be host to a brood of periodical cicadas over springtime, from May until July, roughly. Here, we’ll go over some of the basics on cicadas and what they mean for Nashville’s canopy.
What’s the Difference Between Periodical and Annual Cicadas?
The hum of cicadas rattling in the trees is a familiar sound toward the end of summer. Annual cicadas, also known as “dog day” cicadas, tend to live in the background, being heard but not really seen. Periodical cicadas are the ones that swarm an area once every 13 or 17 years for several weeks in mid-to-late spring.
There are several distinct differences between these two types of cicadas:
Reproductive cycles – Annual cicadas live underground for just a few years as larvae and adolescents (known as nymphs), and some of these cicadas will emerge every year. Periodical cicadas, on the other hand, emerge only on 13- and 17-year cycles.
Brood size – While annual cicadas show up every year, they aren’t as numerous as periodical cicadas, whose high numbers and long subterranean lives are thought to be an evolutionary tactic to avoid having their population decimated by predators and to ensure a successful next generation.
Body size – Annual cicadas, which are less numerous and regularly present, are larger (usually about an inch and 3/4) than periodical cicadas (about 3/4 of an inch to 1 and 1/4 inch).
Body color – Periodical cicadas are actually more visible than annual ones; periodical cicada species have black and orange bodies with red eyes, while annual cicadas blend into the leafy treetops with green and brown coloration and black eyes.
Emergence season – Annual cicadas love the warmth of the mid to late summer, but periodical cicadas come above ground in the spring of their emergence years when the ground temperature reaches 64 degrees Fahrenheit.
Loudness – All cicadas share their signature rattling chorus, which males make to attract females. However, the number of cicadas present in a given area will affect how much that sound compounds. The light background hum of annual summer cicadas is pleasant compared to the clamor of the sheer number of periodical cicadas that emerge at once.
Cicadas in the Ecosystem
While we might find them annoying or creepy, cicadas actually contribute their own services to the wider ecosystem. Female cicadas lay their eggs in the branches of trees, then the larvae fall to the ground after hatching and burrow into the soil. Cicadas then spend most of their lives under the tree that bore them, where they feed on the sap of the roots, causing no damage to the tree itself. While they live underground, they aerate the soil as they move around (improving oxygen content and water penetration), and after their breeding season, uneaten cicadas die and decompose, releasing nutrients back into the soil, which the trees can then use to grow.
When the nymph cicadas emerge from the ground, they drop their adolescent shells and engage in their mating ritual. The males rattle to attract females, and once their mating is complete, they finish out their life and die. Some cicadas are gobbled up by predators before they can mate, serving as a feast for large birds like geese and ducks, many mammals, and fish! Bo Arrington, ISA board-certified master arborist, shared with us that one of the groups who really appreciates the cicada hatches are fishermen: “It’s actually one of the most coveted events for fly fishermen; bass, carp, and trout go crazy for them!”
Some human enthusiasts even eat them, grilling or sautéing the insects. While pet owners might worry about their cats or dogs snacking on a few cicadas, they are generally harmless to ingest, although smaller animals might be sensitive to the shells (especially if they have a similar shellfish allergy) or the foreignness of the large insects to their digestive systems. If your pet is showing signs of illness after ingesting a cicada, it’s recommended to have them checked by a veterinarian to be sure they’re treated properly.
Do Cicadas Damage Trees?
Cicadas might damage young or small trees that haven’t yet developed thick bark and sturdy branches. Arrington advised us on how to safeguard saplings and understory trees: “One thing people can do to protect small or young trees is to cover them in fine nets or wrap the branches in burlap. Smaller ornamental trees are more likely to be killed by cicada damage than larger, established trees.” Native tree populations have millennia of experience with cicadas and can generally tolerate the massive reproductive season of periodical cicadas.
What Does It Mean When You Start Hearing Cicadas?
Cicadas in Tennessee are a yearly occurrence, but whether those cicadas are annual or periodical is another question. When we start hearing the cicadas, it means that their last emergence was a successful reproductive season. They play their unique role in the canopy ecosystem as important sources of food for wildlife above ground and aerators down below. Knowing this, we can appreciate their yearly song and do what we can to manage through the periodical brood swarms, both of which remind us that nature is thriving!
Check out NTCC’s tree sale if you’re in the market for new additions to your yard, and consider volunteering with the Nashville Tree Conservation Corps to help us get more trees in the ground across the city. If you haven’t already, sign up for our email newsletter to stay on top of canopy news and tree care tips!