Thursday, May 12, 2016

Brood V of the 17 Year Cicadas are Emerging in the Mid-Atlantic Region

Many call periodical cicadas "17-year locusts" or "13-year locusts", but they are not the locusts of the Egyptian Exodus, which are actually a type of migrating grasshopper. However, if you live in the area if this year’s emergence, when the 17 year cicadas arrive in the next several days it may indeed feel like a plague. In Virginia there are seventeen broods of the 17-year cicada and thirteen broods of the 13-year cicada. Every year they will emerge somewhere in the state, but unlike 2013 this one is modest in the Commonwealth. This citizen scientists in Maryland have already reported the emerging brood called Brood V, and though I am out of the “designated area” I saw a couple this morning.

Some counties in Virginia have several broods that impact all or part of the county. The 2013 emergence was huge in this region and impacted Loudoun, Prince William, Fairfax and Fauquier. The Magicicada Brood V that is emerging this year is much smaller in this region.

The 17 year periodical cicadas or Magicicada adults have black bodies, red eyes and orange wing veins, with a black "W" near the tips of the forewings. They look much scarier than they are in reality- they are mostly harmless and are a favorite of amateur entomologists. The annual Cicada or dog day cicada are related to the periodical cicada. As their name implies appear every summer during the long, hot dog days of July and August. Those cicadas have two- to five-year life cycles, but their broods overlap and some appear every summer. That is not the Cicadas that are now emerging from the ground.
from VA Tech

Right now mature nymphs are emerging from the soil and climbing onto nearby vegetation and other vertical surfaces. They then molt to the winged adult stage. The emergence is tightly synchronized, with most adults appearing within a few nights. Adult cicadas live for only two to four weeks. When the 17 year periodical cicadas emerge the density can be shocking and noisy. It is common to have tens to hundreds of thousands of periodical cicadas per acre, but there are records of up to a million and a half periodical cicadas. Half of the cicadas are “singing.” Male cicadas sing quite loudly by vibrating membranes on the sides of their abdominal segment. Male songs and choruses are a courtship ritual to attract females for mating. The males’ choruses have been known to drive people to distraction-stay inside with the windows closed and if need be use a fan for white noise- it will be over soon. After mating, females lay their eggs in narrow young twigs slicing into the wood and depositing up to 400 eggs in total for each female in 40 to 50 locations each.

It is the egg laying that does most of the damage associated with periodical cicadas. Cicada eggs remain in the twigs for six to ten weeks before hatching. The nymphs do not feed on the twigs. The newly hatched, ant-like nymphs fall to the ground where they burrow 6 to 18 inches underground to feed on roots. Mature trees and shrubs usually survive even dense emergences of cicadas without long term damage, possibility even benefiting from pruning some lower twigs and braches. However, in the summer of a large emergence like 2013 around here many deciduous trees turn brown due to the breakage and death of peripheral twigs caused by the females laying their eggs and the emergence of the nymphs. Only young trees are usually permanently damaged and that is because so much of these trees are small twigs and branches. In 2013 I planted too early and lost a few new trees.

Apparently because of their long life cycles and the synchronization of their emergence, periodical cicadas do not have natural population control by predators, even though everything from birds to spiders to snakes to dogs eats them opportunistically when they do appear. The massive emergence is believed to overwhelm predators and most of the periodical cicadas survive to mate and reproduce that is the whole point of the emergence. Cicadas are not poisonous and do not have a stinger. Their survival and expansion strategy is based purely on numbers.

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