Friday, May 6, 2011

Periodical Cicadas Emerging

Figure 1. Adult periodical cicada 
(Photo: David McKeithan)
We’ve had several calls lately about the emergence of periodical cicadas. These insects, which spend the first 13 or 17 years of their life underground, often emerge suddenly and in large numbers. As a matter of fact, the cicadas are emerging right now at my parents’ house in Waxhaw, NC in such large numbers that, as my mom put it, “it sounds like a UFO is hovering above our house!”

Figure 2. Newly molted periodical cicada
(Photo: David McKeithan)
Cicadas are relatively large insects with transparent wings held roof-like over the body (Fig. 1). Some species of cicadas show up every year, but the periodical cicadas show up in certain areas every 13 or 17 years. After spending all those years living in the soil, from depths of two to twenty-four inches, mature nymphs emerge from about a one-half inch diameter hole in the ground. Nymphs crawl a foot or more up tree trunks or other vertical surfaces where adults emerge leaving their nymphal skins behind. The newly emerged adult is soft and white for some time (Fig. 2) before the exoskeleton hardens and becomes darker (Fig. 3).

Figure 3. Adult periodical cicadas
(Photo: David McKeithan)
Mated females cause damage to the twigs of deciduous trees on which they lay their eggs (Fig. 4). Twigs slit by the female's ovipositor will frequently have leaves that wilt and die. This damage to the twigs may cause some of them to die, but the injury is usually inconsequential. Eggs hatch 6 to 8 weeks, at which time the young larvae burrow into the soil where they will spend the next 13 or 17 years, depending on the species.

Periodical cicada damage to twig
(Photo: Tim Tigner, VA Dept of Forestry)
The use of insecticides in school settings for cicadas is usually not necessary or practical. The damage done to healthy trees is minimal. Trees and shrubs that are vulnerable (i.e, young or newly planted) may be covered with a covered with a mesh cloth to prevent the females from laying eggs. 
Powered by Blogger.