RENEE MONTAGNE, HOST:
For many, this is the sound of summer.
(SOUNDBITE OF INSECTS CHIRPING)
MONTAGNE: Perhaps surprisingly, most of us don't know what makes this summer chorus. At least that's what dozens of you said in emails asking for help identifying the sound. Listener Philip White sent us an email with his guess, cicadas. So we consulted the experts.
LAUREL SYMES: People sometimes describe night-calling insects as cicadas. But typically, cicadas call during the day, and what we're hearing at night are crickets and katydids.
MONTAGNE: That's Laurel Symes. She's an evolutionary biologist at Dartmouth College. She says katydids are big, green bugs. And Symes explains how you can tell their sound.
SYMES: It makes a call like, Katy did; she didn't; she did; she didn't, especially if you have two individuals going back and forth.
MONTAGNE: And the crickets...
SYMES: There is sort of a high-pitched (imitating cricket chirping) sound on a lot of the recordings. And that's usually tree crickets. So if you have one tree cricket, you hear (imitating cricket chirping). But if you have lots and lots and lots of tree crickets, all those sounds blend together. And what we hear at a distance is just this continuous background hum.
(SOUNDBITE OF INSECTS CHIRPING)
MONTAGNE: That chorus can be heard as late as October. But come the first hard frost, this summer sound disappears.
SYMES: Because when it gets really cold, it's enough to kill the insects. And so in one night, the night chorus can be gone. And it will be quiet until the next summer.
MONTAGNE: Quiet, ah. That was biologist Laurel Symes. And this was part of our Close Listening series. For more information on the series, follow the hash tag, #decodenature on Twitter. Transcript provided by NPR, Copyright NPR.