By Master Gardener Sandy Vanno
Periodical cicadas are native to the eastern United States and occur nowhere else in the world! These fascinating insects emerge in enormous “broods” that are one of nature's great wonders but can also be a cause for concern for some people.
There are seven species, three of which have 17-year life cycles and four of which have 13-year life cycles.17-year cicadas generally have a northern distribution, while 13-year cicadas are more southern, although they exhibit considerable overlap in the middle of The United States from North Carolina and Georgia west to Missouri, and both types may be found in the same forest. Brood X (10), known as the “great eastern brood”, is a large brood that emerges across 15 states.
Adult periodical cicadas are about 1-1/2” long, mostly black with reddish-orange eyes and wing veins. They may be confused with various species of annual cicadas, which are larger with greenish wing veins, and emerge from July-September instead of late May-early June.
Periodical cicada nymphs live in the soil at depths of 2 to 24 inches, where they feed on sap from tree roots. When nymphs determine it is the year to emerge, they burrow to about an inch beneath the soil surface in April. Exit holes may be noticeable in a lawn, which may be unsightly but does not permanently harm the turf. If the ground is too damp, the mature nymphs build a protective earthen turret, which can help identify where cicadas will emerge. When the soil temperature reaches 64°F the nymphs exit the ground and crawls a foot or more up tree trunks, weeds, or other upright objects. This usually occurs in late May or early June, depending on how warm or cold spring temperatures are. The adult cicadas then shed the nymphal exoskeleton, which is left behind, in an hour or less. At this point, the cicadas are soft, white, and unable to fly as the exoskeleton takes a few hours to harden. Once the exoskeleton is hardened the adults are capable of flying but are rather clumsy fliers and often collide into objects. This makes them easy prey for various birds, which gorge themselves on the cicadas. While stragglers may emerge a few days earlier or later, the main emergence of a periodical cicada brood often occurs over one or just a few nights.
Soon after emerging, males begin to sing while females remain silent. About 10 days after emergence, females mate and begin depositing eggs in twigs and branches of various trees and woody shrubs. Using a saw-like ovipositor, a female cicada cuts a small pocket into a twig, in which she deposits 24-28 eggs. She then moves forward, cuts another pocket, and lays more eggs. The pockets are placed close together in a straight row and sometimes form a continuous slit for 2-3 inches. Adult periodical cicadas live for 3-4 weeks above ground and each female can lay 400-600 eggs over a lifetime. The eggs hatch 6-7 weeks after they are laid. The white-ant-like nymphs work their way out of the twig slits, drop to the ground, and enter the soil where they feed on fluids from plant roots for the next 17 years.
Periodical cicadas are clumsy fliers and easy prey for a variety of birds and other insect-eating predators. Mass emergence of them is therefore thought to be a form of predator avoidance – if millions of cicadas emerge at the same time, predators quickly eat their fill and leave the vast majority of them alone to reproduce. Early or late-emerging cicadas are generally not numerous enough to successfully reproduce because most of them are eaten. While individual periodical cicadas typically live for 13 or 17 years, mass emergences of periodical cicadas usually happen somewhere in the eastern United States every year.
Cicadas do not bite or sting and are not a threat to people or pets, although consumption of large numbers by pets should be discouraged. However, they can do damage to young trees, which results in twig and stem dieback. Large, otherwise healthy trees, can withstand this damage without long-term consequences, although they may be aesthetically unpleasing for a time. Small trees that have a majority of the branches within the cicadas' preferred size range can be severely affected and sometimes be killed. This is especially true of small, stressed trees, such as those that have been recently transplanted or are balled and burlapped in preparation for sale or transplantation. Deciduous trees are preferred hosts, especially oaks, maples, apples, cherry, hawthorn, redbud, and other trees that have twigs of the appropriate size (3/16” to 7/16” in diameter), although cicadas are not too picky and have been recorded to oviposit in more than 80 different species. Shrubs are rarely harmed. Also, they do not target herbaceous plants (annuals and perennials, including vegetables and herbs) for feeding or egg-laying. They do not usually deposit eggs in coniferous trees, although coniferous hosts are not totally unknown. Ornamental ponds should be covered with screening or plastic mesh to prevent cicadas from accumulating. Large numbers of decomposing cicadas could cause problems with oxygen depletion in the water. Clean pool skimmers/filters frequently during cicada emergence to keep them from getting clogged.
Control - If possible, transplanting trees should be avoided in the fall and spring before a periodical cicada emergence. Pruning trees should also be avoided during this time as branches injured by cicadas can be pruned out after they die off. Trees under 10 feet tall can be protected by netting with 1/2” mesh, or breathable fabric, to exclude the cicadas. Apply before emergence and keep on the 4-6 weeks they're present. In most cases, netting trees is more effective than spraying chemical pesticides. However, chemical pesticides can be used to reduce damage to small trees when netting is not practical, such as in a large fruit orchard. The pesticide is often needed to be applied every 2-3 days as new cicadas immigrate from nearby trees. But chemical pesticides can also kill beneficial mites and insects, which can exacerbate pest issues later in the season. Pesticides are not recommended for large, otherwise healthy trees, as they can withstand the pressure of cicada oviposition with little to no long-term effects.
“Periodical Cicada”; Penn State Extension
“Cicadas”; University of Maryland Extension
Last updated November 9, 2021