Periodical Cicadas Emerge in Georgia This Year

This year, 2021, an unusual biological event will take place in North Georgia: the emergence of the 17 year periodical cicadas. These insects will have spent the last 17 years underground, sipping sap from tree roots. They are the offspring of cicadas that called, courted and laid eggs in 2004 and then died. How many will emerge and where is not precisely known, but there could be millions or more.
Where should you go to experience this emergence? Forested areas in the top tier of counties in Georgia. 

The CicadaMania website has lots of information and is updated frequently. (link) 

Temperature is a big factor determining the emergence. A correspondent in northern North Carolina tells me that they have emergence holes with immature cicadas waiting inside.

What are Cicadas?
Most people encounter cicadas in two ways: 1) a clamorous, droning noise coming from trees during the dog days of summer, and 2) empty, brown shells clinging to tree trunks. Many have not made the connection between the two. The ugly shells are the exoskeletons left behind when the adult cicada crawls out of them in its last molt. The noise is caused by groups of male cicadas gathering in the same tree, each producing a courtship song to attract a mate. The individual calls blend together to make a deafening, continuous roar that attracts female cicadas.
 

Recordings. Radiolab has a podcast interview with a cicada researcher that begins at 9:50. (link)

Cicadas in Georgia. Georgia has two distinct kinds of cicadas. Those that appear every year are called annual cicadas; those that appear every 13 or 17 years are called periodical cicadas.

Annual cicada (one of 15 species in Georgia)
Note the dark eye color and the green wing veins; the green, brown and black pattern on the thorax and abdomen.
(photo courtesy of Don Hunter)

Annual cicadas. Annual cicadas emerge from the ground every year, usually in the dog days of July and August. Because of the time of year they make their appearance they are often called "dog day" cicadas, but annual cicadas is an equally appropriate name.
In Georgia there are around 15 species of annual cicadas. They are mostly colored with shades of green, brown and black and have dark eyes.
 

Periodical cicada; note the red eyes, orange wing veins and black body.
(Katja Schulz from Washington, D. C., USA, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons)

Periodical cicadas. Periodical cicadas appear at intervals of 13 or 17 years, in April and May or June. They are mostly black in color, have bright red eyes and orange wing veins. The adults emerge by the millions. There are three species of 17 year cicadas that emerge together. Similarly, there are three species of 13 year cicadas that emerge together. (Recently, a fourth species of 13 year cicada has been recognized. It has not been found in all the Broods).

Life cycle: A female cicada lays her eggs in slits she makes in the terminal branches of trees. After a week or so the eggs hatch and the young nymphs fall to the ground and burrow into the soil. (The nymphs look like miniature cicadas, but lack wings and genitalia.) When the tiny nymphs find the fine roots of grasses, they insert their sharp pointed mouthparts and begin sucking sap. As they grow they must periodically shed their exoskeleton. The exoskeleton has limited ability to stretch and it must be replaced in order to keep up with the growth of the nymph. The process of replacing it is called molting and the nymphs will molt a total of five times. As the nymphs get larger  they abandon the grass roots and seek out tree roots to feed from. 

A cicada nymph before the last molt. The brown exoskeleton will become the "cicada shell" when it is left behind after the adult emerges.
(USDAgov, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

The last molt takes place above ground when the cicada nymph digs out of the soil and crawls up a nearby tree trunk. The exoskeleton of the nymph splits down the back and the adult cicada crawls out. The newly emerged adult is pale and soft bodied, with small, sack-like wings. It pumps body fluids into the wings, stretching them to their adult size. The wings and adult exoskeleton take a few hours to harden and darken. Then the cicada is ready to find a mate and reproduce.
Annual cicadas spend 2 to 5 years as nymphs underground. Periodical cicadas spend 13 or 17 years as nymphs.

 

Periodical cicada emergence tunnels. Some are open, with the nymph still inside. Others are still closed, capped by soil pushed upward by the nymph.
(photo courtesy of C. Beane; taken 4/27/21 in Elkin, NC)

 

When cicada nymphs are ready to emerge they abandon the tree roots they have been feeding on and dig their way to the surface. They will only emerge when the soil temperature is warm enough. They sit inside their tunnel, waiting for a warm day, to emerge, climb a tree and molt for the last time. The nymphal exoskeleton (the "shell") is left clinging to a tree after the adult cicada struggles out, as seen in the first part of this short David Attenborough video. (link) 

Where periodical cicadas are found. Periodical cicadas are only found in the eastern United States, from the New England states to Georgia and extending as far west as eastern Nebraska, Kansas, Oklahoma and Texas. Those with the 17 year periodicity are found in the northern part of that range; the 13 year cicadas are found in the southern states, except Florida, which does not have any

Periodical cicada broods. Periodical cicadas do not emerge simultaneously over their entire geographical range. Instead, the emergence in any single year is in a smaller geographical area within the overall range. All the periodical cicadas that emerge in the same year are said to belong to the same "Brood." There are 17 possible Broods of 17 year cicadas; 13 possible Broods of 13 year cicadas. Some Broods occupy large areas, others have a more restricted distribution. Some are apparently extinct. The Broods are numbered with Roman numerals, I through XVII for the 17 year species and, for the three known broods of 13 year cicadas, XIX, XXII XXIII.
A map for Brood X can be found at this website.
A recently published, high resolution map of multiple cicada broods can be found at this website.

Why are cicadas sometimes called locusts? A locust is a type of grasshopper. (All locusts are grasshoppers, but not all grasshoppers are locusts.) Unlike cicadas, grasshoppers have chewing mouthparts and are members of the Order Orthoptera (crickets, katydids, grasshoppers). Cicadas belong to the Order Hemiptera (true bugs, cicadas, aphids, leaf hoppers, plant hoppers) and have piercing, sucking mouthparts. Locusts periodically emerge in terrific numbers and lay waste to the vegetation in their area. It is likely that an emergence of enormous numbers of cicadas caused the early English colonists to associate the cicadas with one of the eight plagues that the Bible says God sent to Egypt. Neither locusts nor periodical cicadas occur in England, so the colonists had never experienced such an eruption of insects. They seized upon the biblical plague passage to incorrectly call the cicadas locusts. 

 

More Information:

This website has a lot of periodical cicada information, great photos and information about preventing possible damage to your trees. (link)
 

A great site for exploring information about cicadas of all kinds. (link)

FINE Things 46

1. Can moving threatened species from one location to another actually be detrimental? Could conservationists be spreading parasites and/or diseases? (link)

2. Coffee is dominated by one species, C. arabica. But arabica plants do not grow well at higher temperatures, such as those expected under climate change. Another species of coffee can tolerate higher temperatures and its beans seem to be as flavorful. (link)

3. Environmental DNA - how a tool used to detect endangered wildlife ended up helping fight the COVID-19 pandemic. (link)

4. 142 years ago, a professor at Michigan State buried a large number of bottles. Each bottle contained 50 seeds of 21 different kinds of plants. His purpose was to see how long the seeds remained viable. Initially, every 5 years one bottle would be dug up and the seeds tested. Later the interval was extended to 20 years. This year another bottle was unearthed. (link)

5. Antibiotics and the Foods We Eat. When it comes to the animals that humans raise to eat, a quick look at their numbers proves sobering. Worldwide, there are some 650 million pigs, 1 billion heads of cattle and 26 billion chickens. Such numbers cannot be achieved by traditional animal rearing practices that use extensive surface areas. (link)

6. No Transgenerational Effects of Chernobyl Radiation Found, The genomes of the children of people exposed to fallout from the Chernobyl nuclear accident appear to carry no trace of the incident. (link)

7. What a Video Game Can Reveal About Monkeys' Minds. Researchers find that the animals can account for others' behavior and circumstances in their strategies.
(link)

8. Interactive Infographic: How Salt Transforms Coastal Forests. Rising sea levels are pushing salty tides and storm surges farther inland, leading to the forest death and a shift from forested habitats to marsh. (link)

9. DNA of Giant 'Corpse Flower' Parasite Surprises Biologists. The bizarre genome of the world's most mysterious flowering plants shows how far parasites will go in stealing, deleting and duplicating DNA. (link)

10. All the world's penguins in one short video! (link)

11. Will reforestation offset our carbon emissions? (link)

12. Naturally GMO: Crops steal genes from other species to accelerate evolution. Grass crops borrow genes from their neighbors, giving them a competitive advantage, a new study has revealed. (link)

13. Bile and Potatoes, 1921. One hundred years after its invention, BCG has stood the test of time as a vaccine against tuberculosis. (link)

 

14, Radiolab podcast featuring a 17 year Periodical Cicada song segment begins at 9:50. (link)



 

FINE Things 45

1. Some Magnolia flowers have built-in heaters. (link)

2. Michigan State botanist Beronda Montgomery this month published a book that explores what plant behaviors and adaptations can teach people. In an article for The Conversation, she creates a rich picture of how plants can communicate, share resources among themselves and fungi, and self-isolate when necessary. (link)

3. The New Historian of the Smash That Made the Himalayas.
About 60 million years ago, India plowed into Eurasia and pushed up the Himalayas. But when Lucía Pérez-Díaz reconstructed the event in detail, she found that its central mystery depended on a broken geological clock. (link)

4. Why Earth's Cracked Crust May Be Essential for Life.
Life needs more than water alone. Recent discoveries suggest that plate tectonics has played a critical role in nourishing life on Earth. The findings carry major consequences for the search for life elsewhere in the universe. (link)

5. Researchers identify a bacterium that enables its host to breathe nitrate instead of oxygen. (link)

6. Years after Marie Curie won her second Nobel prize, she couldn't afford a gram of radium, the element she codiscovered. It cost today's equivalent of $1.3 million. This podcast recounts how a magazine editor named Marie Meloney raised the money in small donations from women around the US - enough to buy a fresh gram of radium for Curie's research and to establish a trust fund for the scientist and her daughters, one of whom would go on to earn a Nobel Prize of her own. (There's a transcript if you can't listen.) (link)

7. Rosemary recommends this Zoom recording that discusses the history of alpha-gal sensitivity: how it was discovered and the ensuing problems it presents to medical practice. (link)

8. From The Guardian: Just 3% of world's ecosystems remain intact, study suggests. Pristine areas in the Amazon and Siberia may expand with animal reintroductions, scientists say. (link)

9. Another piece from The Guardian. 'A poor man's rainforest': why we need to stop treating soil like dirt. The mysterious world under our feet is under threat. Protecting it is as vital as tackling the climate crisis, scientists warn. (link)

10. Pharma and the US government plan for covid-19 booster shots. It's unclear how long protections against infection will last from the initial vaccinations. People could need booster shots, but only time will tell. (link)

 

11, Gary Crider recommended: Ants that can regrow their brains. (link)

12. Those mysterious "Fairy Circles" are back in the news with a new hypothesis of how they are formed, at least in Australia. Known for years only in Namibia, the Australia proposal could be different from how they are formed in Namibia. (link)

13. Find an earlier summary of the causes of Fairy Circles here.

FINE Things 44

1. Rosemary liked this video of a scarlet siphonophore. (A siphonophore is in the phylum Cnidaria (jellyfish, sea anemones, corals, Hydra, siphonopores (think Portuguese Man-of-war)). (link)

2. Are Huge Tree Planting Projects More Hype than Solution? High-profile programs aimed at planting billions of trees are being launched worldwide. But a growing number of scientists are warning that these massive projects can wreck natural ecosystems, dry up water supplies, damage agriculture, and push people off their land. (link)

3. Kelp Pathogen Has Spread Across the Southern Ocean. (link)

4. Got Cicadas? Take a Picture and Help Entomologists Map Their Arrival. Periodical cicadas will emerge soon in N. Georgia. Here's a chance to help scientists determine their exact distribution. (link)

5. Early Humans' Brains Were More Apelike than Modern. Impressions that ancient brains left in fossilized skulls reveal that the first human ancestors to migrate out of Africa had much more primitive brains than previously thought. (link)

6. Bees in Your Backyard; an Intro to Bee Diversity in the U.S.; webinar with author and biologist Olivia Carril, coauthor of the book. (link)

7. I found this webinar really interesting: Intro to Phenology with Denise Ellsworth. A webinar about phenology and how to develop one for your area, using Ohio as an example. (link)

8. Ted LaMontagne likes this story by UGA graduate student James Chapin. It's about Florida's role as a beachhead for invasive species. (link)

9. Local honey is often recommended as a treatment for hay fever. Does it have any effect? (link)

10. A world in a bottle of water. Revolutionary techniques using traces of environmental DNA are analyzing entire ecosystems "from microbes to whales." (link)

11. Animal culture is so common that even fish and flies have it. (link)

12. Bees learn to play golf and show off how clever they really are. (link)

13. Human-like intelligence in animals is far more common than we thought. Stories of clever animals abound, from pigs playing video games to monkeys trading mobile phones – now tests reveal that they don't merely act on instinct but can think flexibly, like us. (link)

14. Invasive earthworms, invasive plants and their effects on native species. (link)

15. How a Carnivorous Mushroom Poisons Its Prey. Scientists have known for decades that oyster mushrooms feasted on roundworms-and they've finally figured out how their toxins work. (link)

 

16. Crown-shyness, tree crowns avoid colliding in 3D. A new metric quantifies the "puzzle-shape-ness" of tree crowns. (link)