When do cicadas come out?
If you live in cicada country, you might have already met Brood X, the 17-year cicadas. If not, you will soon enough. Whether you think they’re fascinating, disgusting, or just plain noisy, you have to admit that they have an incredible built-in alarm clock. They spend the first seventeen years of their life underground—basically hibernating—but without fail, they emerge in the seventeenth summer to mate and die. So how do cicadas keep track of the time? Obviously, you can’t ask them. But you can conduct experiments where you play around with the cycles of nature, like light, temperature, and plant life cycles, to see if that changes the cicada clock. As you heard, the clock still isn’t fully understood. But it looks like at least two different steps are involved. First, the cicadas’ bodies have to count from one year to seventeen years. They seem to do this by keeping track of the sap cycles in the roots of the trees. We can guess this because when you plant trees in a lab, and use sh