These mayflies are typically small to medium-sized, ranging from 3 to 12 mm. In most genera, the antennae are 2-3 times longer than the width of the head. Gills are found on abdominal segments 1 or 2 through 7, displaying variable shapes. There are 2-3 caudal filaments present. These mayflies are frequently abundant and can be exceptionally small. They are proficient swimmers, which is why they are referred to as minnow mayflies. In polluted streams, certain species of these mayflies can be notably common.