Why Are They Called "Mayflies," Then?

You know it's a lot of insects when they show up on radar:

A large mayfly hatch occurred along the Mississippi River Friday evening, June 30th. The hatch began just after sundown, around 9 PM, and continued through the early morning hours. Those with plans outdoors Friday evening on and along the Mississippi River certainly noticed the huge swarm of mayflies, and their attraction to light. Some roads across the Mississippi River in and around La Crosse were covered with bugs, piling into "drifts" on bridges over the Mississippi River and its tributaries. Local businesses with high intensity lighting soon found large piles of dead mayflies accumulating under the lights by midnight.

See the incredible radar loop, too: it's like a snowstorm, only bugs.