In late April, listen for a loud racket coming from the trees.

Brood X of the 17-year periodical cicada will emerge in 2021 in counties along the Ohio River and southeastern Kentucky. The infestation intensity will vary widely from none to very heavy within different parts of the same county.

The millions of periodical cicadas that emerge is visually striking. In addition, the sounds they make can be deafening. The males fly to high branches in the sun and sing together in choruses that attract females.

The male uses specialized structures on his abdomen to make the sound. They are harmless to humans, pets, and livestock, according to Dr. Ricardo Bessin, entomologist with the University of Kentucky Cooperative Extension Service. They cannot sting and are not known to cause any disease.

However, they cause damage to trees and shrubs.

Every year we hear the annual, also referred to as dog-day, cicadas in the summer, which do not come out in large numbers like periodical cicadas.

The two cicadas also look different.

The periodical cicadas have red eyes and clear wings with orange veins. The annual cicadas have green eyes and green veins in clear wings. The periodical cicadas are 1.5 inches long and annual cicadas are larger, at 2 to 2.5 inches long.

Also, the periodical cicadas appear in April to June; the annual cicadas appear in July to September.

The life cycle of the periodical cicadas will begin in late April or early May with their emergence. It takes about three weeks for them all to come out. They emerge from the ground as mature juveniles and attach themselves to an upright surface.

The back splits on the last nymphal skin, and the adult comes out. They leave empty brown skins lying everywhere. The adult rests there for several hours until their bodies and wings have expanded and are dry and hard.

After a couple of days, they will mate. The male dies after mating. The female looks for places to lay her eggs and then dies.

The females usually prefer to lay eggs on grapevines, oak, hickory, apple, peach, and pear trees. They first slit the bark of, usually, pencil-sized twigs and then insert a row of eggs into the wound. Eggs hatch in six to 10 weeks.

Nymphs fall to the ground and burrow down to the root system where they stay for the next 17 years, feeding on the sap of tree and shrub roots with their piercing-sucking mouth parts.

Periodical cicadas can cause physical damage to small trees or shrubs if too many lay eggs in its twigs; such damage can cause the breaking of peripheral twigs, referred to as “flagging.”

Because this damage can easily destroy the current year’s growth, increased pruning is required to remove damaged areas. This type of damage is most significant on newly set or young trees and shrubs.

Mature trees and shrubs, however, usually survive even dense emergences of cicadas without apparent distress. Their presence in a tree does not mean that damage has occurred.

This can be difficult to believe in the month or so following a large emergence when many deciduous trees turn brown due to the breakage and death of peripheral twigs. As serious as it may appear, such damage is apparently minor but will reduce the current year’s growth.

It is recommended that new orchard or landscape plantings be delayed until after periodical cicada activity has ended for the season because young trees may be harmed by severe flagging.

Because egg-laying is the real danger from these insects, consider protecting young trees and shrubs when the first male singing is heard. A week or so after emergence, females are ready to lay eggs.

The young and small trees and shrubs can be covered with a protective netting or cheesecloth. Be sure to secure the covering around the trunk to prevent cicadas from climbing up to the limbs.

This covering stays on for the next four to six weeks towards the end of June or until egg-laying is complete. The netting or cheesecloth is used because it allows light to reach the plant’s leaves.

In addition, pruning the twigs with egg slits prevents cicada nymphs from feeding on the roots of young trees. This has to be done within three weeks of the end of egg laying.

Even though time consuming, this may be best when considering the production life and long-term value of backyard fruit trees, especially. Vigor reduction of small trees can occur by large numbers of nymphs feeding over several years.

According to Dr. Bessin, insecticide applications are generally of limited use in protecting trees from damage, especially where cicadas are very abundant. Repeated treatment would be needed to deal with new arrivals.

Orchards under a routine spray schedule should be treated about twice a week during peak cicada activity, if the pesticide label allows. Spray requirements will vary according to the outbreak’s intensity.

Recommendations are available for their management through the Cooperative Extension Service on fruit trees. Net or use cheesecloth to protect young fruit trees.

For more information about Brood X of the 17-year periodical cicadas, contact the Daviess County Cooperative Extension Service at 270-685-8480 or

Annette’s Tip

Periodical cicadas are sometimes mistakenly called locusts. Early settlers made incorrect assumptions that these insects, which come out in hordes overnight, were the locusts referred to in plagues of locusts. These insects are not related.

Annette Meyer Heisdorffer, PhD, is the horticulture extension agent with the Daviess County Extension Office. She can be reached by calling 270-685-8480.

Annette Meyer Heisdorffer, PhD, is the horticulture extension agent with the Daviess County Extension Office. She can be reached by calling 270-685-8480.


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