They are cicadas. From gardenersnet.com: "They are sometimes called "17 Year Locust." Although, they are not related to locusts."

Locusts are grasshoppers. So calling a cicada a "locust" is false. But I guess it's sometimes used colloquially. Like when we were kids andcalled horned lizards "horny toads." When in fact they're not frogs or toads at all. And we knew it, too. image