Imagine a creature that emerges from the ground in massive numbers, almost like a scene from a zombie movie. This spring, the Eastern United States will witness such an event with the arrival of periodical cicadas. These insects have fascinated and sometimes frightened people for generations, but they are not dangerous. Let’s dive into the amazing world of cicadas and learn what makes them so unique!
Periodical cicadas are a special type of insect found in the United States. They belong to the genus Magicicada and are known for their long life cycles. Depending on the species, they spend either 13 or 17 years underground, feeding on a liquid called xylem from tree roots. This is the longest underground development period of any insect on Earth!
After spending years underground, cicadas emerge in the spring when the soil temperature reaches about 64°F. Millions of them come out at the same time, shedding their skins and transforming into winged adults. This synchronized emergence is like a giant party, with male cicadas gathering to sing loudly and attract females. Their calls are among the loudest in the insect world, thanks to a special organ called a tymbal.
There are seven species of periodical cicadas, divided into three groups: Decim, Cassini, and Decula. These groups evolved millions of years ago and have different emergence cycles of either 13 or 17 years. Cicada broods are groups of cicadas that emerge at the same time, often including several species. For example, in 2024, both a 13-year brood and a 17-year brood will emerge together in different parts of the U.S.
One of the biggest mysteries about cicadas is how they keep track of time so precisely. Scientists think they might count the seasons by sensing changes in the trees they feed on. An experiment with peach trees showed that cicadas might use these seasonal changes to know when to emerge. Despite this, the exact mechanism remains a mystery.
Researchers believe that cicadas’ long underground life is due to their poor diet of xylem, which requires a long time to mature. Emerging in large numbers also helps them avoid predators, as it overwhelms any animals that might want to eat them.
After mating, female cicadas lay their eggs in tree branches, which can sometimes harm the trees. The eggs hatch into nymphs, which fall to the ground and burrow into the soil to start their long underground journey. However, a specific fungus can infect cicadas, affecting their behavior and spreading among them.
Despite their loud and unusual behavior, cicadas play a crucial role in the ecosystem. They help recycle nutrients, provide food for other animals, and even promote tree growth. Their emergence is a natural wonder that benefits the environment in many ways.
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Draw and label the life cycle of a cicada, from egg to adult. Use different colors to represent each stage and include key details about what happens during each phase. This will help you visualize and understand the unique development process of cicadas.
Organize a class activity where you simulate the emergence of cicadas. Assign roles such as cicadas, predators, and trees. Use this role-play to explore how cicadas overwhelm predators and the importance of their synchronized emergence.
Choose one of the cicada broods and research its history, emergence patterns, and geographical location. Prepare a short presentation to share your findings with the class, highlighting the differences between 13-year and 17-year broods.
Conduct a small experiment or research project to explore how cicadas might track time. Consider factors like temperature changes or tree growth cycles. Present your hypothesis and findings to the class, discussing the scientific methods used.
Write a short essay or create a poster on the ecological importance of cicadas. Include how they contribute to nutrient cycling, their role as a food source, and their impact on tree growth. Share your work with the class to promote understanding of their environmental benefits.
This video is supported by the Real Science Patreon page. Join us on Patreon for bonus content and community perks you can’t get anywhere else. This spring, the Eastern United States will experience an emergence of a creature appearing in numbers not seen in centuries. They will come at night, bursting through the ground like an army of the undead. These creatures have haunted American settlers for generations, with early colonists calling them a plague and even using them as indicators of impending war. With their red eyes and papery brown husks, it’s easy to see why they inspired so much fear and fascination.
However, periodical cicadas are not zombies, predictors of war, or a ravenous plague of locusts. They don’t have teeth and cannot transmit diseases, making them harmless to humans, aside from their sheer abundance. The seven species of periodical cicadas in the United States all belong to the genus Magicicada, and they are unlike any other organism. Depending on the species, they spend either 13 or 17 years underground with no light, movement, and very little food. No other insect on Earth takes this long to develop underground. They survive by feeding on xylem, which is liquid from tree roots.
Then, on one momentous spring night, millions of them emerge simultaneously, living their lives in complete synchrony. They climb up the nearest vertical surface and shed their skin, emerging in their final winged form. Trillions of cicadas will emerge at the same time across the U.S., and once they leave the ground, the real party begins. Male cicadas gather in chorus centers to broadcast their calls to attract females. This song is one of the loudest known among insects, produced by an organ unique to cicadas.
How do they tell time so precisely? How do they produce such loud sounds? And why do they take so long to develop before emerging all at once? Before we delve into the life cycle of periodical cicadas, we need to clarify the differences between species and broods. There are seven species of periodical cicadas, divided into three groups: Decim, Cassini, and Decula. The Decim group split off first about 3.9 million years ago, followed by the Cassini and Decula groups 2.5 million years ago. Over time, these species evolved to have lengthy developmental stages of either 13 or 17 years, unlike many other cicada species that only require one year.
Cicada broods are groupings of periodical cicadas that emerge simultaneously, usually comprising several different species. In the spring of 2024, both a 13-year brood and a 17-year brood will emerge at the same time. Brood 19 is the largest, extending from Maryland to Georgia and from Iowa to Oklahoma, including four 13-year species. In Northern Illinois, Brood 8 will emerge, featuring three 17-year species. You won’t see all seven species emerge as adults at the same time again until 2037.
Despite their different emergence times, the life cycles of 13-year and 17-year cicadas are surprisingly similar. Cicada nymphs go through five instars or developmental stages, but since these stages occur underground, they are challenging to monitor. An entomologist in Connecticut, Chris Meyer, conducted an experiment from 1979 to 1995, digging up cicada nymphs each year to observe their growth and development. He found that older nymphs took longer to transition to the next developmental phase and that their growth rates varied.
As nymphs reach their fifth instar and the 13th or 17th year of their cycle, they wait for the soil to reach the right temperature. When the soil warms up to about 64°F, they tunnel through the dirt, sometimes creating mud turrets. They climb onto the nearest vertical surface and begin the final stage of development. Their skin splits, and they emerge, inflating their tiny wings with fluid. Once their exoskeleton hardens, they are ready to start the courtship process.
Despite our understanding of their emergence triggers, the exact mechanism cicadas use to keep track of years remains a mystery. There are thousands of cicada species worldwide, most of which have yearly cycles. The North American periodical cicadas are unique with their 13- and 17-year cycles. One hypothesis suggests that cicadas might count in intervals of four, emerging either four years early or late based on their internal timing.
Researchers have proposed that cicadas may be counting seasons based on the trees whose roots they feed on. Cicadas drink xylem, a nutrient-poor fluid produced by trees. To test this hypothesis, researchers conducted an experiment with peach trees, creating two different light and temperature conditions. The cicadas placed near the trees with a normal cycle emerged as expected, while those near the accelerated trees emerged a year early, suggesting they may be using trees to mark time.
Another mystery is why cicadas spend so long underground before emerging all at once. Some researchers believe their poor diet of xylem requires a long maturation period. Additionally, emerging in large numbers may help cicadas evade predators, as their irregular emergence cycles prevent predators from becoming accustomed to them.
Cicadas are known for their loud mating calls, which can reach sound levels of 100 dB, comparable to a hair dryer or subway train. Male cicadas produce their calls using specialized organs called tymbals, which create a loud sound when rapidly contracted. Each species has a distinct call, helping females identify the right mate.
The mating process takes about an hour, after which the female lays her eggs in tree branches. She saws an opening in the wood with her ovipositor, depositing 10 to 20 eggs at a time until she has laid around 500 eggs. This process can harm the tree branches, leading to a phenomenon known as flagging, which can also result in egg mortality.
Once the eggs mature over two months, they drop to the ground as nymphs, burrowing into the soil to begin their long life underground. However, a specific fungus targets periodical cicadas, rendering them sterile and hijacking their behavior. Infected males may exhibit female mating signals, spreading the fungus further.
Despite their loud and unusual behavior, periodical cicadas play a vital role in their ecosystem. They help unlock nutrients, serve as food for various animals, and contribute to soil health. Their emergence can lead to increased growth in trees, benefiting the environment.
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Cicada – A type of insect known for its loud, buzzing sound, often heard in the summer, and its life cycle that includes long periods spent underground. – Example sentence: The cicada’s loud song filled the summer air as it emerged from the ground after years of development.
Underground – Beneath the surface of the earth, where many organisms, like cicadas, spend part of their life cycle. – Example sentence: The cicada nymphs live underground for several years, feeding on the sap from plant roots.
Emerge – To come out from a hidden or covered place, such as when insects like cicadas come out from the ground. – Example sentence: After spending 17 years underground, the cicadas finally emerge to molt and reproduce.
Species – A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. – Example sentence: The periodical cicada is a unique species known for its synchronized emergence every 13 or 17 years.
Life – The existence of an individual organism, characterized by growth, reproduction, and response to stimuli. – Example sentence: The life cycle of a cicada includes several stages, from egg to nymph to adult.
Xylem – The vascular tissue in plants responsible for the transport of water and nutrients from the roots to the rest of the plant. – Example sentence: Cicada nymphs feed on the xylem of tree roots while they develop underground.
Broods – Groups of cicadas that emerge in the same year, often named and tracked by scientists. – Example sentence: Brood X is one of the largest and most famous broods of periodical cicadas in the United States.
Ecosystem – A biological community of interacting organisms and their physical environment. – Example sentence: The emergence of cicadas can have a significant impact on the ecosystem, providing food for predators and nutrients for the soil.
Nutrients – Substances that provide nourishment essential for growth and the maintenance of life. – Example sentence: When cicadas die, their bodies decompose and add nutrients to the soil, benefiting the ecosystem.
Behavior – The way in which an organism acts in response to a particular situation or stimulus. – Example sentence: The mating behavior of cicadas involves males producing loud calls to attract females.
