The periodical cicada, Magicicada septendecim, is poised to emerge
this spring at the U.S. National Arboretum. This fascinating event
occurs every 17 years, and is a real treat for anyone who has an interest
in entomology. A group of periodical cicadas that live in a specific
area, often covering parts of several states, emerge at the same time and
are known as a brood. There are at least 30 known broods, and Brood
X, which emerges this year, is the most spectacular and occurs over a large
part of the mid-Atlantic region and parts of the Midwest.
Over the past 17 years, these insects have been quietly feeding on the sap of tree roots. When they emerge in mid May, they won't eat at all. They devote their time instead to mating and laying eggs. It is the female's egg laying that creates the most visible damage. Each female cuts slits in the twigs of trees and lays eggs in them. The eggs hatch and the young nymphs fall to the ground to find a root to feed on for the next 17 years. The wounded branches are weakened and often break off or wilt. While the damage is noticeable, it is not life threatening except for very young or very small trees.
The list of trees that sustain damage is long. Oak, dogwood, ash, maple, hickory apple, birch, cherry and black locust are all injured. In fact, up to 200 species have been known to be damaged. Only those with gummy sap, such as pine and spruce, are immune. The periodical cicada has a number of natural enemies and predators, but none of are able to provide adequate control for the massive populations that appear in a short time frame. Their sheer numbers ensure that many adults can survive to lay eggs. It is thought that periodical cicadas evolved the curious habit of appearing in synchronized broods to overwhelm their predators.
What can you do to prevent cicada damage to your trees?
If you want to plant a new tree, delay planting until fall or next spring, after the adult cicadas are gone.
If you've already planted a tree, or have an existing small tree that you'd like to protect, plan on protecting trees with either cheesecloth or plastic netting. The openings in the netting should be no more than one-half inch wide. Mesh netting may be available at your local garden center or hardware store. One quarter inch mesh netting is illustrated here.
Cut a piece of netting big enough to cover the entire tree canopy. Wait to trim it down to the right size until you have it in place; it is very difficult to estimate how much netting will be needed. Place it carefully over the branches of the tree. You may need to use a broom or rake to safely get the mesh into position over the tree. A small step ladder may be helpful.
Be sure to cover the canopy completely so the cicadas cannot crawl through voids in the mesh. Fasten the netting securely to the trunk just below the lowest branch point using twine or jute. The netting should remain in place from the time of cicada emergence until they are gone, about 8 weeks total.
For more information on periodical cicadas, click here [this will open a new browser window containing an off site Univ MD webpage].
Links back to:
Last Updated April 30, 2004 3:11 PM
URL = ../../Gardens/faqs/CicadaNet.html