by Mary Free, Certified Master Gardener
By now you have seen or heard (reports about) the periodical cicadas of Brood II. You also may remember back to 2004 and the Brood X cicadas (the largest and most widespread of all broods). Periodical cicadas occur in cycles of 13 or 17 years. There are about five broods of 17-year cicadas that appear in different years in Northern Virginia. Adults emerge in late spring/early summer and live for two to four weeks. They spend most of that time mating and reproducing. Since the adults eat very little, most of the damage you will find is to tree twigs in which female cicadas lay their eggs. This damage will not harm most mature trees but young trees with smaller branches (about the diameter of a pencil) or vines could be at risk. If you are concerned about newly planted trees, you can place a fine netting over the top of the tree, securing it around the trunk to prevent cicadas from climbing under it. You should remove the netting at the end of June. (Refer to Virginia Cooperative Extension Publication 444-276, Periodical Cicada, http://pubs.ext.vt.edu/444/444-276/444-276.html).
When cicada eggs hatch, nymphs drop from the tree branches and burrow into the ground maybe as deep as 3 feet. They attach themselves usually to tree roots on which they feed. This is unlikely to harm the tree. Nymphs will molt several times as they develop, and as they get bigger, they move closer to the surface. However, for 17 (or 13) years, periodical cicadas live out of sight (and out of mind) underground. When the time comes, their last molt will be above ground. When they shed their nymphal exoskeletons, they have their signature red eyes but their bodies are white. As their wings expand, their bodies gradually turn black and that is when we pay attention to them.
Predators also attend to them: parasitic wasps, flies and mites attack the eggs, digging/tunneling mammals and centipedes eat the nymphs, and birds (primarily) and small mammals eat the adults. Cicada killers also attack the adults but only those that emerge late in the cycle because the appearance of cicada killers coincides annually in summer with that of their prey, the dog-day (not periodical) cicada. Despite these predators, the sheer number of periodical cicadas overwhelms and guarantees that we will eventually see many of their offspring.
Dog-day or annual cicadas, which we see and hear during the “dog days” of every summer, are larger than periodical cicadas and a green/brown color with dark eyes. Like the periodical cicadas, the annual nymphs develop underground feeding on root sap, but their life cycle is considerably shorter. After only two to five years, dog-day cicada nymphs crawl out of the ground and climb a tree or the like and split and abandon their exoskeletons. Adults do not cause as much damage to trees as the periodical cicadas and they have natural controls like cicada killers. According to Wendi Hartup of the North Carolina Cooperative Extension, “in a typical season 100 female cicada-killers will clear over 16,000 cicadas from the surrounding area.” (Watch Out For The Cicada-Killer!
Cicada killer wasps may look menacing because of their size, but they are unlikely to bother people. Although males might appear aggressive, like all male bees and wasps, they cannot sting. Females tend to be docile and are unlikely to sting unless handled carelessly. Cicada killer wasps build their nests underground near trees that shelter cicadas. Tell-tale dirt mounds surround their burrows. They especially like full-sun areas under lawns where grass is sparse or has been cut too short (good cultural practices can prevent establishment of colonies) as well as areas under shrubs or flower beds (applying a 3-inch layer of hardwood mulch should discourage them). Drenching a site with water may encourage them to abandon their nest.
A female cicada killer stings and paralyzes a cicada, which she carries back to her underground nest and seals in a cell with an egg. The larva that hatches eats the living but paralyzed cicada as it grows. Larvae overwinter (adults do not) in hard cocoons and emerge the next summer as wasps to start the cycle again. Adult wasps feed on nectar. So, in addition to controlling cicadas, these wasps are pollinators. If they do nest on your property and are not causing physical damage, consider cicada killer wasps beneficial insects rather than pests and try to tolerate them for the approximately 6 to 8 weeks that the adults are around.
Lastly, remember that neither the periodical cicada nor dog-day cicada pose a threat to people as they do not sting or bite, although periodical male choruses have been known to reach over 90 decibels. In fact, some people eat cicadas, especially those whose skins have not yet hardened. If you wish to test your culinary skills and expand your palate, the best time to catch newly emerged cicadas is early in the morning. (See recipes but also note disclaimers. CICADA-LICIOUS: Cooking and Enjoying Periodical Cicadas at http://www.newsdesk.umd.edu/pdf/cicada%20recipes.PDF)