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Thursday, June 24, 2021

Brood X: The lives and encounters of America’s largest group of cicadas

These are part of a group named Brood X, based on their life cycles and periodic appearances. The cicadas in Brood X number in billions and come out of their underground homes every 17 years.

Written by Mehr Gill | New Delhi |
Updated: June 11, 2021 7:21:58 am
Cicadas cover a plant in Maryland. (AP Photo: Carolyn Kaster)

On Wednesday, US President Joe Biden’s first trip abroad was delayed unexpectedly when a swarm of cicadas bombarded the plane Air Force One, which was about to take off for the UK. Biden had to swat a cicada away when it landed on him at the Joint Base Andrews in Maryland.

Swarms of these insects have been spotted in a number of American states. These are part of a group named Brood X, based on their life cycles and periodic appearances. The cicadas in Brood X number in billions and come out of their underground homes every 17 years.

But what is Brood X?

Cicadas live underground for extended periods of time, typically 13 or 17 years, and feed on roots of trees both underground and above it. The term ‘brood’ refers to a population of cicadas that is isolated from other populations because of differences in their year of emergence or locality.

Brood X is the largest brood of 17-year cicadas and is found in Pennsylvania, northern Virginia, Indiana and eastern Tennessee, according to the US National Park Service (NPS). Last year, another grouping of 17-year cicadas dubbed Brood IX emerged in some states on the east coast of the US.

A map of active periodical cicada broods in the US. (US Forest Service via NOAA)

Among periodical cicadas, there are seven species. There are also some annual cicadas, which come out every year.

Brood X started emerging in May and will be around until the end of June. The time when they decide to emerge is dependent on weather, specifically when ground temperatures reach about 17-18°C.

What do cicadas do underground for 17 or 13 years?

When underground, cicada nymphs go through five stages of development. Once they become adults, which takes about 17 years for some periodical cicadas, the males emerge from underground. While it is not clear why cicadas take so long to develop, some researchers believe that it could be because they want to avoid predators above the soil. When they come out, they shed their exoskeleton (outer skin) to take their winged form.

President Joe Biden, with a brood X cicada on his shirt collar, walks to board Air Force One upon departure, Wednesday, June 9, 2021, at Andrews Air Force Base, Md. (AP Photo: Alex Brandon)

But why do they come out?

Their emergence is to ensure continuation of their species. Male cicadas emerge first and start singing to attract females. Male cicadas produce the loudest sounds in the insect world, the NPS says. Females respond with a clicking sound with their wings. This process lasts for about a month, after which the cicadas die, with most of them having accomplished the task of procreating.

After mating, the eggs are laid in in small twigs and branches. Once they hatch after about six weeks, the nymphs fall to the ground, and burrow their way into the ground. After becoming adults, these nymphs will emerge again 17 years later (or 13 years in some broods).

Some cicadas will be eaten by frogs, fish, birds or raccoons. But they come out in such huge numbers that many will be able to mate and ensuring survival of their species.

Is this brood particularly significant?

Because of their sheer numbers, cicadas in Brood X often make headlines. When the brood last emerged in 2004 in Washington DC, the cicadas made “an impact on the cultural scene, drowning out weddings, clogging pool filters, appearing on t-shirts and hats, showing up in stir-fries and in smoothies by design as well as by accident, and otherwise making their presence known in America’s most political town”, entomologist May Berenbaum wrote in the American Entomologist.

Berenbaum also wrote about references to cicadas in politics. For example, the Republican National Committee once released a video to take a dig at Senator John Kerry (now Biden’s special presidential envoy for climate change). The Committee said: “Like a cicada, Senator Kerry would like to shed his Senate career and morph into a fiscal conservative, a centrist Democrat opposed to taxes, strong on defense… When the cicadas emerge, they make a lot of noise. But they always revert to form, before disappearing again.”

In 1987, President Ronald Reagan used cicadas to criticise the Democratic budget proposals: “Like the cicadas, the big spenders are hatching out again and threatening to overrun Congress.” And in 1902, President Theodore Roosevelt was drowned out by these insects as he was delivering his Memorial Day speech, Berenbaum notes.

Are cicadas dangerous?

Cicadas also do not bite or sting, but when the males sing, their collective chorus can reach up to 100 decibels, a noise level that can possibly cause severe damage if you are exposed to it for several hours. One hundred decibels is equivalent to a jet flyover at 1000 feet, a motorcycle or a powered lawn mower.

The Maryland Department of Agriculture notes that the only harm cicadas can cause is during egg laying when small twigs may be damaged by deep slits cut by the female when she deposits her rows of eggs (a typical female can lay roughly 500 eggs that are laid in over 40-50 different sites). This damage can be avoided by covering very small trees and gardens with fine cloth or netting.

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Can cicadas be eaten?

Some people harvest and eat cicadas by coating them in chocolate, deep-frying them, or using the insects as toppings for a pizza. They are considered to be nutritious and high in protein and some minerals.

The news website quotes anthropology expert Cortni Borgerson from Montclair State University as recommending that cicadas from Brood X be used for a range of recipes — including tempura cicadas, singing sushi and flaming cicada fondue.

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