This type of fly lives for less than a day. It has a shorter lifespan than any other creature.

Don't May Flies often times die within hours after hatching?

You're right, Georgia85!

Most mayfly species live only a few days as adults, but the occasional insect that isn't eaten by predators or otherwise recycled sometimes lands in soft sediment with a chance of becoming a well-preserved fossil. - Cornell University

Adult Mayflies do not feed and live very short lives, many species live only for one or two days but in others the adult life span may be as short as 2 hours or as long as 14 days. Nymphal life cycles can range between 3-4 week to 2.5 years depending on the species. - EarthLife.net

As winged adults, they survive only a few hours or at most a few days, nothing is eaten, nor do they crawl or walk. - Ohio State University(Emphasis mine - DG)

Mayflies

The name Ephemeroptera is derived from the Greek "ephemera" meaning short-lived, and "ptera" meaning wings. This is a reference to the short lifespan of most adult mayflies.

Some species mature quickly, in as little as four weeks, while others develop more slowly (one to four years per generation).

Most adults are delicate insects with a very short lifespan. They do not feed (mouthparts are vestigial), and some species emerge, reproduce, and die in a single day.

Some mayfly species require up to four years to complete development. In that time they may molt more than 20 times. - North Carolina State University, Department of Entomology