The Insane Biology of: The Cicada

This video is supported by the Real Science Patreon Page Join us on Patreon for additional content and community benefits you can't get anywhere else This spring, the eastern United States will experience an invasion by a creature that emerges in quantities that have not been seen in centuries. They will arrive at night, crossing the ground like an army of the living dead. They have haunted American settlers for generations and early settlers called them pests and even used them as an indicator that war was coming with their red eyes and papery brown husks that shed before reaching their final form, it's not It's hard to see why they inspired so much terror and awe, but periodical

cicada

s are neither zombies nor predictors of war or even a ravenous plague of locusts, they don't even have teeth and can't transmit. disease so they are basically harmless to humans in addition to being very deficient.

The seven species of periodic cycads in the United States belong to the genus magi

cicada

and are unlike any other organism; depending on the species, they spend 13 or 17 years underground. With no light, no movement and very little food, no other insect on Earth takes as long to develop when they are underground, they survive by eating xylem, which is the liquid from the roots of trees, and then, on a momentous spring night , millions and millions of them emerge at once. An unthinkable number of organisms living their lives in complete synchrony, then climbing whichever vertical surface is closest, then tearing their skin and bursting into their final winged form.

In total, there will be billions of cicadas emerging at around the same time in the US and once they have left the ground, the real party begins, the male cicadas gather in chorus centers to broadcast their call to the females. This song is one of the loudest known among insects and is produced with an organ that no other insect loves. or hate them, it's hard not to be impressed by these intense, loud, crunchy guys, how come they can tell time so accurately? How are they so loud, and why did they evolve so that it takes decades for them to fully develop and then all emerge?

Immediately before we get to the life cycle of periodical cicadas, we first have to review the difference between the species and the offspring. The whole nomenclature gets a little complicated. There are seven species of periodical cicadas and they are divided into three groups. Desim Cassini and Decula. The Desim group was the first to separate from the others about 3.9 million years ago and then 2.5 million years ago. Cassini and Decula split up and over time each of these species evolved to have extremely long developmental stages that lasted 13 or 17 years instead of just the one year required for many other cicus species each.

On the other hand, they are groups of periodic cicadas that simply appear at the same time. These broods are usually made up of several different species to understand more about the development of the cicadas I spoke with. Dr. Chris Simon, there are many insects that live longer, maybe even some beetles that could live 50 years, but in terms of development from egg to adult, these are the longest known life cycles, but why did some evolve to staying underground for 13 years and others? for 17 because as these cycads evolved something else was happening in North America from 2.6 million to 11,700 years ago, continent-sized ice sheets formed in North America that then underwent repeated expansion and contraction.

Researchers believe that the growth and dissipation of ice may have affected how these cycads evolved. The species were separated from each other as the 17-year-old species are further north than the 13-year-old species; In other words, perhaps they were first geographically isolated by glaciers and then adapted to have longer life cycles because they were in a colder climate. This map shows the geographic distribution of all the different hatchlings we currently know and right now, in the spring of 2024, a 13-year-old hatchling and a 17-year-old hatchling will appear at the same time. Brood 19 is the largest of all broods that range from Maryland to Georgia on the East Coast and Iowa to Oklahoma in the Midwest and includes four 13-year-old species and 8 broods will appear in northern Illinois, including three species of 17 years, you will not be able to see all seven species.

They emerge as adults at the same time again until 2037, and although 13-year cicadas and 177e cicadas develop on different time scales, their life cycles are strikingly similar. Cic nymphs go through five instars or stages of development, but because those five stages all happen underground, they are quite difficult to monitor. An entomologist in Connecticut Chris Meyer conducted an incredible experiment to see what was happening underground from 1979 unearthed 100 cicada nymphs each year for 17 years noted the amount of time it took the nymphs to move from one stage to the next noting that the older they got, the longer it took most of them to move to the next stage developmental.

He also noticed that not all of them were growing at the same rate, an interesting observation that his timing probably isn't related to the size they reach. Near the end of the 17-year experiment in 1995, he noticed that the nymph's eyes changed from white to red, indicating that they would emerge next spring when the nymphs reach their fifth instar and reach the 13th or 17th year of their cycle. They wait for the soil to reach the right temperature at their 20cm depth, the soil needs to warm up to 17.9°C or 64°F, which happens around April or May, then one afternoon they make tunnels.

Through the land, they sometimes even create mud turrets which are basically small towers that rise above the ground as they emerge, climb to whatever vertical surface is closest to them and begin the final stage of development, molting, and this Part of it is a little gross, but it's also super cool, his skin splits along the chest, what we would consider the back, the head and then the body and then the legs move freely while the lining of his breathing tubes or trachea flips over once their small wing has fully emerged. The fins should inflate like little balloons, fluid is pumped through the veins in their wings, causing them to expand once they have fully emerged from their shell, their exoskeleton hardens and darkens and then they are ready to begin the courtship process. , but despite how much we have learned about them, they still hold one of the greatest mysteries of ecology once they have reached their year of appearance.

We know what drives them out of the ground, but we don't know exactly how they keep track of those years. I don't know exactly how they know when to leave. There are thousands of species of cicadas around the world and the vast majority of them have annual cycles. This even includes many cicadas in North America, there are only two other species of periodical cicadas. In the world, in northeast India, there is one known as the World Cup cicada for the way its cycle is related to the football championship, and in Fiji there is one with an 8-year cycle. .

You might notice something about those other two species that both life cycles are based on. at 4-year intervals, but North American periodical cicadas have cycles of 13 and 177e that don't fit that pattern, except that when cicadas lose track of time, they tend to appear 4 years early or 4 years late. One researcher has hypothesized that cicadas could count in intervals of four, although they sometimes come out in odd years, if they are ready to come out early they will come out early, but only in a four year window will they come out four years early or, at times, yes They are not ready for your slave, but even if cicadas could count to four and group those numbers, how would they know when a year has passed?

Surely they can say that the temperature is changing to some extent based on the ground temperature, but being underground. It insulates them from the more extreme seasonal variations that occur in the air. They also can't see any light, so they have no way of knowing when the sun rises or sets. One group of researchers proposed an interesting hypothesis that cycads count the seasons based on the trees whose roots they feed on, if you remember. While we mentioned that cicadas drink xylem, which is one of the two fluids that trees produce, you're probably more familiar with the first, which is sap or, more specifically, it's a thicker liquid and is.

Meanwhile, xylem is much more Nutritional is mainly water with low levels of minerals and other nutrients. Xylem is so poor in nutrients that cicadas couldn't even survive on it if it weren't for the endosymbiotic bacteria they have inside their bodies, bacteria that allow them to create essential amino acids from xylem, but although xylem does not contain many nutrients Tree cycling researchers placed fully grown peach trees in large pots. and created two different light and temperature regimes for them. The first set of trees grew as they normally would with 365 days of light and Four Seasons. The second set of trees were artificially sped up to have twice as many days and more rapidly changing seasons so that they would react as if one year were actually two and this part of the experiment was quite successful with the sped up peach trees leafing and flowering twice a year. year instead of once, although they only produced Once the researchers also collected fruit, 130 cicada nymphs that were in year 15 of their 17-year cycle, 100 of those nymphs went to the trees on the accelerated time scale. and 30 of the nymphs were in normal pots, this experiment was a bit complicated because Apparently, cicada nymphs are difficult to transport from one place to another, they have a really high mortality rate, so only 13 nymphs survived and emerged from the ground of the 130 that were brought to the experiment, but the ones that survived showed something quite remarkable: the cicadas placed near the peach tree with a normal cycle emerged in year 17 as expected, but the cicadas that were placed near the peach tree whose cycle sped up by two emerged exactly 1 year earlier because in their minds 17 years had passed, this seems to suggest that the cicadas are using the trees to mark time, but we still don't know how they keep track of whether 1 year has passed, two or five.

There's probably more going on beneath the surface than we know. Some scientists believe there is some type as well. of communication Underground near the time of their appearance, um, but we don't know that no one has proven that so far the other piece of uncertainty is why they spend so much time underground and then emerge all at once. Some researchers have hypothesized that their xylm diet is so terrible that it takes them a long time to mature, it could also be an effort to break their connection with predators, almost everything eats cicadas, from birds to squirrels and your dog, so It makes sense that cicadas emerge in large numbers. and they have irregular cycles of appearance because they remain underground for so long, predators do not have life cycles related to the growth of cicus, so no predator gets used to them as their main food and because they are very numerous even if they are eaten a ton enough.

You still survive to mate and that mating process is the next part of what makes cicadas so cool or deeply disturbing, depending on your point of view. If you live around cicadas, you probably know that they are very loud, very loud, in fact, if you get close. In a tree full of male cicadas, sound levels can reach 100 dB, which is about the same noise intensity as a hair dryer, a forklift, or a subway train. It's such a loud sound that researchers have hypothesized that it could negatively affect human cognitive function, although the verdict is still out on that, but cicadas don't make noise just to annoy all their neighbors, it's an essential part of of its mating and is different from any other cricket insect and CAD produced its chirps by rubbing its hind legs against each other, male.

Cicadas, on the other hand, have special organs called timbl that allow them to produce the chirping sound. A timble appears on each side of the abdomen and is connected to the timble muscles within the cicada's body; when the muscles contract rapidly upon release, they pull on the ribs. timbls that cause them to click and resonate against the air sacs in their thorax and abdomen, the speed at which they click and the size of their body changes the sound of their call because they have two timbls instead of just oneand because they are able to By pulsing the timble muscles between 3 and 400 times per second, the call is extremely loud despite how small they are and all 17 year old species have calls with different sounds.

Magis sepand desum makes a call that sounds like the word pharaoh magisa Cassini. clicks followed by a buzz and Magis sepand deula only has a series of short chirps lasting 10 to 30 seconds with each round, the difference in those calls is part of how females know they are mating with the correct species, it is always Well To do it right, when you hear this chorus, a female cicada will approach a male cicada and signal that she is ready to mate with a specific wing movement. The mating process lasts about an hour and then the female lays her eggs on the branches of the trees, but not only does she leave them hanging there, she sees an opening in the wood with her opponent, which is a metal reinforced organ, yes Literally, metal researchers found everything from manganese and zinc to iron around the ovipositor, making it strong enough to cut wood, she makes cutting deposits.

Then, 10 to 20 eggs move forward to repeat the process on different parts of the tree branch until all 500 eggs have been laid. Sometimes this kills the branch of the tree, a phenomenon known as flagging, but it is also not good for the cicadas when this happens, as many of their eggs also die, so the females have to choose wisely where to lay their eggs, The eggs mature over a period of 2 months, then are released and fall to the ground as the nymphs quickly burrow towards their dark shelter where they will live for the next 13 to 17 years, but this process is not always the case. go according to plan, a certain species of fungus specifically targets periodical cicadas, the spores fill the abdomen of the cicada, leaving them sterile, but they do not kill the cicada, instead they seem to hijack their brains just like the zombie fungus that It attacks ants in males, it is modified.

The behavior means that they not only call the females, but they also do the female wing-beating signals that attract other males and then the spores are spread further in a big spooky cycle and that's just the beginning of the weirdness that the fungus also doses. cicadas with psilocybin yes, like the psychedelic in magic mushrooms, this tends to happen when fungal infections are more advanced, causing cicadas to completely lose the back half of their bodies, including reproductive organs, even so Drugs make them fly like crazy and still try. to mate even though they no longer have the necessary equipment to do so at the moment, you might be thinking, wow, no thanks.

I don't want my yard or neighborhood to be infested by millions of noisy, creepy mating cicadas, and you know, fair enough, but periodically. Cicadas are not pests, they are actually very good for the environment in several different ways. First, they unlock many nutrients that would otherwise be inaccessible by feeding on low-nutrient xylem fluid and using it to build their bodies. They are something like herbivores. Par excellence, they serve as food for almost everything around them: squirrels, badgers, birds and yes, even humans, some of their predators even have more offspring after the appearance of cicadas because they are very well fed when they shed their skin and then their bodies fall.

The forest floor also provides a large amount of nutrients to both plants and the bacteria and fungi that live in the soil. Soil nitrogen increases 2 to three times its original level in the months after the adults die. , this is great news for trees One study found that sycamores that were fertilized by dead adult cicadas grew about 10% more than controls in the year following the cycads' appearance and this accelerated growth lasted for at least 2 years, so you might think there is an unpleasant or slightly strange noise and you definitely don't want one flying around your house, but periodical cicadas play a vital role in their ecosystem and for that we can be grateful.

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