Common questions
Why do periodical cicadas have such long life cycles?
See the discussion here.
When will the periodical cicadas appear in my area?
See the brood pages for upcoming emergences. Even if the maps suggest that cicadas are going to emerge in your area, remember that cicada populations are patchy, so they may be in woods nearby, but not at your house, etc.
When do the cicadas start to come out?
In the springtime — late April or May in the warmer states and May or early June in the cooler states. (The nonperiodical “annual cicada” species emerge from late June into late summer).
How long will the cicadas be out in my yard/neighborhood/city?
About 4-6 weeks after they first start emerging. Most individual cicadas live only a few weeks, but since they emerge over a period of two weeks or so the whole event lasts longer. The serious noise will get going about a week and half after you first notice them and will last about two weeks more. After that things get a lot quieter.
Why do I hear different sounds?
Each brood typically contains multiple species, and different periodical cicada species have different calling songs. See the species pages for details. In addition, periodical cicadas have complex courtship behaviors, which include multiple types of songs.
How many cicadas will there be?
Although there are a lot of periodical cicadas, they are not generally considered to be insect pests.
It turns out that it is extremely hard to estimate the population sizes of periodical cicadas, for any number of reasons. The oft-quoted figure of densities that can exceed a million per acre comes from a census taken during the 1956 emergence of Brood XIII in Raccoon Grove, IL (Dybas and Davis 1962). Ironically, Brood XIII appears to have gone extinct or nearly extinct in Raccoon Grove in the years since 1956 (Cooley et al. 2016; Karban 2014), so it is clear that periodical cicadas are variable across space and time!
If we accept a rough estimate of one million cicadas per acre… should that be surprising? How many ants are there per acre? How many mayflies? How many fruit flies? Insects often come in large numbers. What’s special about Magicicada is not the large numbers per se, but the periodicity– the predictable, synchronous emergence of large numbers of adults and their near-total absence in the years between (see the “straggler” page for more information).
The state of Delaware is roughly 1.5 million acres in size. If we accept an estimate of a million cicadas per acre and if the total combined area of a periodical cicada emergence is roughly the size of Delaware, then more than a trillion cicadas will be involved.
How loud are periodical cicadas?
Individual periodical cicadas are not as loud as some other cicadas; however, their choruses contain so many individuals that they may reach 90+ decibels as perceived while standing under them. Choruses of the -cassini species can be especially loud, because under just the right conditions, individuals will synchronize their singing and flying activities, leading to loud, pulsating, and frankly overwhelming choruses.
How do I tell the species apart?
There are currently 7 described Magicicada species. You can see their characteristics by visiting the species pages on this site, where you will find photographs, sounds, and distribution maps. The -decim species differ in abdomen color. M. neotredecim and M. septendecim tend to be darker than M. tredecim.
Are periodical cicadas endangered?
Periodical cicadas are not considered to be endangered. However, much remains unknown concerning their biology and ecological interactions. Sheer numbers do not necessarily protect periodical cicadas; after all, passenger pigeons once had enormous population sizes and they are now extinct. The dynamics of some species may involve a “step-function” such that once popuation sized are depressed below a certian level, they quickly go extinct. For example, Brood XI in southern New England became extinct some time after 1954, and all but the core populations of Brood VI became extinct some time during the 1980s. Most astonishingly, the dense population of Brood XIII in Raccoon Grove IL, which was the source of density estimates exceeding a million cicadas per acre (based on a 1956 census; Dybas and Davis 1962) was extinct by 1997 (Cooley et al. 2016). Paradoxically, sometimes extreme densities may lead to the cicadas’ downfall; White et al. (1979) and Cooley and Holmes (2023) documented extremely high levels of mortality in extremely dense populations. Clearly, periodical cicadas are not invulnerable to extinction.
Do cicadas eat?
It is a myth that adult cicadas do not feed. The feeding habits of cicadas are discussed at length in Myers (1929). While cicadas do not have chewing mouthparts, they feed from plant vessels called xylem, which transport the relatively watery xylem fluid. A cicada (adult or nymph) feeds by piercing xylem with its proboscis (mouthparts) and ingesting the fluid (Marlatt 1923, Hepler et al. 2023). Feeding by periodical cicadas has not been demonstrated to affect trees and shrubs much, possibly because the cicadas take only a small fraction of the fluid passing through the xylem. Since xylem fluid is generally watery (at least during the growing season when trees are fully leafed out), it is also a fair question as to whether cicadas are ingesting xylem fluid primarily for nutrition, primarily for water balance, or some combination of both. Since cicadas feed on fluid, they also secrete fluid waste products (sometimes forcibly; see Challita and Bhamla 2024), and it is not uncommon to walk under an active chorus and experience “cicada rain”- the combined waste excretion of all the active cicadas above!
Can I eat periodical cicadas?
There are two ways to answer this question. The first is an ethical approach: Should you eat, for entertainment purposes, a long-lived insect whose populations can clearly be driven extinct? That’s a question you have to answer for yourself. The second approach is a food safety approach. Periodical cicadas have been shown to be mercury bioaccumulators (Heckel and Keener 2007, Heckel et al. 2007, Keener et al. 2007). Given that 1) periodical cicadas have been demonstrated to contain mercury residues; 2) there is no way for the average person to judge the mercury content of any particular periodical cicada; and 3) other food safety characteristics of periodical cicadas are untested, then eating them clearly involves a degree of risk that is difficult to quantify.
Will cicadas hurt my perennials/annuals?
Probably not, cicadas have little interest in these plants (except if any are woody). You may see teneral (newly emerged) cicadas sitting on such plants, or emerging on them, but they will soon move up into the trees.
Will periodical cicadas hurt my young trees?
Possibly. Adult cicadas singing and flying and feeding on young trees are very unlikely to do any damage. However, females do pierce/cut small branches on woody plants to insert their eggs, and if too many cicadas do this the branches may weaken, die and/or break off. The best way to prevent this is to cover such young plants with bird netting (pictured below) or cheesecloth, but before going to this trouble wait until you see how many cicadas are out in your immediate area (female cicadas will not begin laying eggs until at least one week after they first emerge, so there is no hurry). Cicadas do not usually move more than a few hundred meters to lay their eggs.
What about fruit trees?
Periodical cicadas can damage fruit trees or woody vines, in the same way that they damage young or delicate trees. This website, from Virginia Tech, discusses the effects of periodical cicadas on vineyards. Using netting to exclude the cicadas is the best solution.
Can the cicadas hurt me?
No. Cicadas don’t bite or sting defensively, and they are not toxic or poisonous.
I saw lots of cicadas emerge but they all disappeared and I can’t hear any singing — where did they go?
Newly emerged cicadas (teneral cicadas) take about five days of good weather before the males start singing (Cooley and Marshall 2001). All cicadas have such a teneral period, but the teneral period in periodical cicadas appears to be of unusually long duration. Tenerals move higher into the trees when they have hardened enough to climb and remain relatively inactive, presumably while they finish maturing. Many of the early-emerging cicadas are eaten by birds as well-look for discarded wings on the ground under the trees.
I hear a loud repetitive noise at night, is this cicadas singing?
In the US, there are no cicadas that typically sing as night (though many do have periods of intense activity at dusk). When Magicicada populations are very dense, some individuals may utter short bursts of sound during unusually hot nights or near bright lights, but this behavior is not typical. Most noises at night are crickets, katydids, or frogs.
Can cicadas see (i.e., did it have to land on me)?
Cicadas have excellent vision. Cicadas have five eyes (two large red compound eyes on the sides of the head, and three small ocelli (simple eyes) located in a triangle on the front of the head). Periodical cicadas simply don’t much care what they land on, since in natural circumstances everything they land on is a tree; don’t take it personally when periodical cicadas land on your head/pet/car etc. Even the nymphs can see when they emerge from their burrows to metamorphose – they can head towards a tree (or your leg!) – anything vertical – in the near-darkness from many meters away.
Why do I hear cicadas every year?
There are 150 or so species of cicada in the U.S. (including species of Neotibicen, Okanagana, Diceroprocta, Cicadetta, Neocicada, Cacama, Okanagodes, Magicicada and other genera). Only the seven Magicicada species have synchronized development and periodical emergences (meaning that all individuals in a population are always the same age). The rest of the species (the so-called annual cicadas) have unsynchronized development, so some individuals mature in every year and we hear them every summer.
What’s the best terminology for talking aboout them?
Cicadas do not “swarm”, “invade”, or “overrun” (if they emerge aboveground, they have been there the whole time, just underground), nor are they a “plague” (Biblical plague locusts were grasshoppers; Kritsky 2004). Cicadas do not hatch out of the ground (they hatched from eggs in tree branches 17 years ago), and they do not “hibernate” (they are underground actively feeding). When they moult to become adults, the correct term for that process is “ecdysis.”
What purpose do they serve?
This question is difficult to answer from a scientific point of view because biologists explain organisms as products of natural selection, the evolutionary process in which traits that increase reproductive success tend to be preserved in future generations. However, in biology we do examine the effects that cicadas and other species have on each other and on their environment, and this is related to what people often have in mind when they ask about the purpose of a given species. Periodical cicadas are exploited as a food source by a wide variety of species, but only underground or microsymbiotic organisms can evolve to specialize on them since they appear aboveground so rarely. The tunnels of nymphal cicadas aerate the soil and presumably influence soil ecology and tree growth. The twig damage caused by female oviposition actually acts like a pruning for some trees, stimulating future growth. For many people, periodical cicadas are a marvel of nature, a source of many intriguing evolutionary puzzles; or, for some, just a nuisance.
How do periodical cicadas affect ecosystems?
Periodical cicada emergences provide a bounty of easily accessible food for birds and other predators, and birds have been shown to switch their diets to favor periodical cicadas during an emergence (Getman-Pickering et al. 2023). The net results of such diet switching are the other insects are released from predation pressure and thus indirectly benefit other potential prey. Periodical cicadas also move resources from belowground to aboveground pools as they emerge, returning the resources belowground when they die. Periodical cicada emergences are followed by increases in soil microbial biomass and nitrogen availability (Yang 2004, Setälä et al. 2023). However, understanding the effects of periodical cicadas on forests is a complicated balance between the benefits of resource pulses and the detriments of herbivory (Yang and Karban 2009). Some studies show no obvious effects of periodical cicada emergences tree growth (Setälä et al. 2023) while others do (Yang and Karban 2019; Koenig et al. 2023) and still others suggest that hosts modify their phytochemical defenses in response to periodical cicadas (Perkovich and Ward 2022).
Will the cicadas be affected by climate change?
Yes… but they always have been. It’s complicated…