Periodical cicada (Magicicada sp.). Photo: Pennsylvania Department of Conservation and Natural Resources – Forestry , Bugwood.org
Updated: May 19, 2021
The 17-year periodical cicadas in Brood X will emerge when the soil 8” below the surface reaches 64 degrees Fahrenheit. The 2021 emergence has begun in some areas of Maryland as of mid-May.
This is a natural and fascinating occurrence! Millions of cicadas synchronize their emergence to overwhelm predators. Adult cicadas will be active above ground until about the end of June.
Cicadas are not harmful to people or pets. They are a valuable food source for birds and other animals. Do not use pesticides on them.
Cicadas do not cause severe damage to most garden plants. Females prefer to lay eggs in young trees with branches about the diameter of a pencil up to 1/2 inch. Young trees can be protected using netting with ¼-inch or smaller openings.
Cicadas are large charismatic insects in the order Hemiptera. They have sucking mouthparts which they use to feed on the xylem (water transporting tissue) of trees.
There are two types of cicadas commonly found in the eastern United States:
The dog-day or annual cicada, Neotibicen canicularis, occurs every summer.
Periodical cicadas (also known as “17-year locusts,” even though they are not locusts) emerge every 17 years based on the timing of different broods. Brood X will emerge in spring 2021 and is comprised of three species- Magicicada septendecim, Magicicada cassini, and Magicicada septendecula..
Cicada nymphs (immatures) live underground and emerge from the soil at the end of April to the beginning of May. After molting into adults, individuals move or fly to nearby vertical structures, especially shrubs and trees. Males will start their droning mating song to attract females. This is accomplished by vibrating membranes located on the sides of the insect beneath the wings.
Appearance and life cycle of cicadas
Adults vary in size and color according to species. All have prominent bulging eyes and semi-transparent wings held roof-like over their large bodies.
Adult dog-day cicadas are about one and one-half to two inches long with brown or green, black and white body markings.
Adult periodical cicadas are slightly smaller, with black bodies, reddish-brown eyes, and orange wing veins. Their wings will have a black ‘W’ marking on the front wings.
A week after they emerge, the adult cicadas will mate and the females deposit eggs in groups on twigs near the end of branches of more than 200 kinds of trees.
The eggs hatch in about six weeks.
The young or nymphs drop to the ground where they burrow into the soil and feed on the sap of tree roots. Nymphs resemble wingless adults, are tan – brown with stout bodies, and have strong front legs that are specialized for digging and tunneling in the soil. They undergo four molts (growth spurts) while underground.
For the periodical cicada, this will take 17 years. They will emerge in large numbers known as broods. Broods II, V, X, XIV, and XIX are found in Maryland. Brood X will emerge in Maryland in 2021. Brood II emerged in 2013 and will emerge again in 2030. It is not uncommon to have a few periodical cicadas emerge a year ahead or behind the rest of the Brood.
During the spring mature cicada nymphs will tunnel to the soil surface and emerge. They crawl onto tree trunks, posts, and other upright structures and after a short period molt or shed their skin to become winged adults. The empty skins are left clinging to objects.
Emerging cicada. Photo: Joseph OBrien, USDA Forest Service, Bugwood.org
Cicada nymph: Photo: Paula Shrewsbury, Ph.D., University of Maryland
Annual or dog-day cicada adult. Photo: David Cappaert, Bugwood.org
The only damage cicadas cause to plants results from the egg laying habits. Female cicadas use an appendage, called an ovipositor, to gouge longitudinal slits in twigs into which they then deposit eggs. The ovipositor cannot harm people. Adults do not feed on leaves. If they feed at all, it is by sucking plant fluid from tender young twigs.
Cicadas pose no health threat to people or pets, although consumption of large numbers by pets should be discouraged.
Periodical cicada female laying eggs into stem. Photo: Pennsylvania Department of Conservation and Natural Resources – Forestry, Bugwood.org
Egg laying damage to a tree twig. Photo: Jim Baker, North Carolina State University, Bugwood.org
Twigs with many slits often break or hang down from the tree, a condition known as flagging. This damage is not serious. The trees will easily replace branches that have been broken or “pruned” by cicadas.
Young or newly planted trees may be killed, or their growth stunted if this type of injury is extensive during brood years. These plants may be protected by covering them with netting or a breathable fabric (see Management below).
Cicadas have been known to lay eggs on over 200 types of trees to some extent. Some common trees that are most susceptible to cicada damage include oaks (Quercus), maples (Acer), cherry (Prunus), and other fruit trees, hawthorn (Crataegus), and redbud (Cercis). Evergreens are rarely used for egg laying.
Tree branches damaged by cicada egg laying. Photo: Jim Occi, BugPics, Bugwood.org
Flagging damage on maple tree. Photo: David L. Clement, University of Maryland
When large numbers of nymphs emerge from the soil, exit holes may be noticeable in a lawn. Several weeks before emergence, some nymphs construct mud chimneys over the emergence hole. These mounds may be 2-3 inches high and 1-2 inches wide with a hole approximately 1/2 inch wide in the center. The activity may be unsightly but does not permanently harm the turf.
Cicada emergence holes. Photo: M.K. Malinoski, University of Maryland Extension
Control is not necessary on established mature trees.
Insecticides are ineffective for significantly reducing cicada abundance and damage. Insecticides also pose a risk to people, pets, beneficial insects, and birds.
If you intend to plant trees or shrubs in a year when periodical cicadas emerge, consider delaying planting until fall when the cicadas are gone.
Small ornamental trees, shrubs, and fruit trees may be protected by covering them with insect netting sold in garden centers, nurseries, and online. It was observed in 2004 that insect netting with openings ranging from 1/4-in. to 3/8-in. (0.6-cm. to 1.0 cm.) prevented injury to small trees. Bird netting openings are too large to exclude cicadas. Tulle and other breathable fabrics are available that can be draped over small or newly planted trees and shrubs and held to the ground with rocks, bricks, or landscape pins or secured to the base of the trunk to prevent cicadas and wildlife from becoming trapped. The plants should be protected from the time cicadas emerge until they are gone 6-8 weeks later. If left on too long, barriers may physically impede new foliage/stem growth, reduce air circulation (which can promote fungal infection), and shade leaves which will later become sunburned when their full-sun exposure is resumed. Barriers may also prevent pollination, depending on plant flowering times.
Shrubs are rarely harmed. Any visible injury can be easily trimmed away later.
Cicadas do not target herbaceous plants (annuals and perennials, including vegetables and herbs) for feeding or egg-laying. They may climb onto them for support, but won’t harm them.
Organic mulches spread around garden and landscape plants, up to a 3-in. depth, will not interfere with the cicada lifecycle. Prop up or remove any items in your yard that cicadas might fall on.
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.
Common questions about periodical cicadas
What geographic areas do the periodical cicadas affect?
Periodical cicadas found in eastern North America. Within this region, there are different groups called broods that emerge on different 17-year cycles. Broods II, V, X, XIV, and XIX are found in Maryland with Brood X being the largest.
How long will periodical cicadas be out?
Adult periodical cicadas live between 2 and 6 weeks after they emerge from the ground. Adults will begin emerging in May and will last through mid-June.
How are periodical cicadas different from the cicadas I see every summer?
Periodical cicadas are smaller and have much more red-orange coloring than the common, large, green “dog day” cicada (genus Tibicen) we see and hear later every summer. Dog-day cicadas are not periodical. Although their life cycle is typically 2-3 years long, we see some emerging every summer.
How many cicadas do we expect to see this year?
Cicada emergence density can be as high as 1 million per acre. (An acre is a little smaller than a football field!). However, how many we will see this year depends greatly on the amount of urbanization, deforestation, or fire that has occurred within the last 17 years.
Will periodical cicadas eat or damage my flowers, shrubs, or trees?
Periodical cicadas do not damage flowers, but they may damage newly planted or young trees and some shrubs. Damage results from female cicadas laying eggs in small twigs and branches, not from adult feeding.
Do cicadas bite or sting?
No. Cicadas do not sting like wasps and bees. Female cicadas have a blade-like organ called an ovipositor that they use just for laying eggs in twigs. Adult cicadas may make a loud buzzing sound if handled, but cannot bite or sting.
Why do we only see periodical cicadas every 17 years?
By coming out en masse, periodical cicadas are able to avoid or overwhelm enemies. No predator can possibly eat that many cicadas, so chances of individual reproduction and survival increase.