Cicadas are insects that spend most of their lives underground and emerge from the soil mainly to mate. (AP/File)
A brood of periodical cicadas, noisy insects that breed underground for as long as 13-17 years are expected to emerge into some states on the east coast of the US this year.
This year, the grouping dubbed Brood IX will emerge after spending 17 years underground, into states including Southwest Virginia, parts of North Carolina and West Virginia. The emergence of over 1.5 million cicadas per acre is expected. According to Virginia Tech, people living in these areas will experience a “unique natural” phenomenon that has not occurred in most of the area since 2003.
What are cicadas?
Cicadas are insects that spend most of their lives underground and emerge from the soil mainly to mate. Once out of the ground, their life span is fairly short, somewhere between two-four weeks.
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Doug Pfeiffer, a Fruit Entomologist at Virginia Tech, writes in his blog that there will be major outbreaks of periodical cicadas in 2020 and 2021. There are three species of 17-year cicadas and three species of 13-year cicadas. In the blog, Pfeiffer goes on to explain that originally 30 broods of periodical cicadas were defined, mostly separated by geography and the time they emerge from the ground. At present, there are about 15 active broods of these cicadas as some have gone extinct. The insects are found in the America’s as well as New Zealand and Australia.
The name 13 and 17 year refers to the number of years that cicada nymphs take to reach adulthood. It is not clear why their development period is so long, researchers suspect that it may be linked to avoiding predators above the soil. During this time underground the nymphs feed on sap from plant roots. After this developmental period, the cicada nymphs construct a “cicada hut” and burrow their way out from the soil and climb onto any nearby tree or vegetation, a fact sheet published by the Virginia State University states.
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A BBC Earth video described the adult cicadas as “clumsy” and “very edible”, due to their lack of defences because of which they “virutally offer themselves to their attackers” which may include turtles and other inhabitants in a forest. Even though many cicadas are eaten by their predators, their “relentless” stream renders their predators full and overwhelmed, to the point of bursting, giving the survivors a chance to achieve their purpose of mating.
What happens when cicadas emerge?
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After emerging from the ground in billions, the cicadas shed their exoskeletons or outer skins to take their winged form. Their exoskeletons are frequently found attached to tree trunks and twigs. The emergence of cicadas is often “tightly” synchronised, with most adults appearing within a few nights. The lifespan of adult cicadas is short, about two to four weeks during which time they feed relatively little and mate. Male cicadas “sing” to attract the females, the collective chorus of these male cicadas is very loud and can reach up to 100 decibels, which is as much as a powered lawnmower.
After mating, the females lay their eggs in twigs that are ½ to ¼ in diameter. One female is capable of laying over 400 eggs in 40-50 different sites. The eggs remain in the twigs for six to ten weeks before they hatch and after hatching the nymphs fall to the ground where they burrow 6-18 inches underground to feed and emerge 13 or 17 years later, depending on their grouping.
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The egg-laying by the cicadas causes significant damage to small twigs. They damage many ornamental and hardwood trees, especially newly planted fruit and ornamental trees such as apple, dogwood, peach, cherry and pear among others, which are the most seriously damaged.
