This is Viewpoints Explained…
Last spring, billions of cicadas broke out of the ground across the U.S. it was one of the largest – and loudest – cicada takeovers in recent memory. this mass emergence was caused by two different variations of cicadas coming up at once: one on a thirteen year cycle, the other appearing every seventeen years.
But their timing wasn’t a coincidence. It was the result of one of nature’s most mysterious internal clocks. these insects spend nearly their entire lives underground and survive by feeding on xylem sap – a nutrient-rich liquid found in tree roots. According to researchers, cicadas may be keeping time by noticing subtle differences in how their food tastes. each spring, as trees bud and bloom, the xylem sap briefly becomes thicker and richer in nutrients. This change acts like a yearly signal and scientists believe that cicadas keep track of this number. Once it hits thirteen or seventeen, depending on the species of cicada, they tunnel up from the ground and start the brief, noisy business of mating and laying eggs.
And this mass exodus from the dirt is strategic. When millions of cicadas appear all at once, predators can’t possibly eat them all. it’s a phenomenon in nature called predator satiation. Still, some big questions linger. out of the more than three thousand known cicada species around the world, only nine follow this kind of schedule. Why so few and what do the rest do? Scientists don’t fully know these answers yet.
What they do know is that what happened last summer, the mass arrival of two cicadas on different cycles, won’t happen again for more than two hundred years.
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