Because adult mayflies live for such a short time (typically a few hours to 2 days), adult mayflies do not eat. In fact, the adults of many mayfly species do not have mouths or digestive systems because of their short lifespan.
Mayfly nymphs are aquatic. They eat weeds or algae and debris found on rocks or other surfaces.
Larger mayfly nymphs are predators and may catch smaller insects or aquatic larvae.