There are about 70 North American species in this family. Larvae tend to be found in gravel-bottomed streams, with woody debris, or among roots along banks; however, some can be found in lentic situations. Mature larvae are 4–15 mm long. They tend to be clingers and moderately fast swimmers. Most feed by collecting and gathering food, however, some scrapeperiphyton from rocks or gather particles of detritus, others filter particles from the water. The gills are often forked, giving them the name “Pronggills”. We like to refer to their gills as deciduous, because they are extremely fragile and fall off the insect readily, like autumn leaves. They have relatively flat bodies, and thus can be easily mistaken for Heptageniidae, however, they can be distinguished because the mandibles protrude at the side of the face making them visible dorsally.
Wings developing in wing pads. Mouthparts suitable for chewing. Gills present on tops and sides of abdomen. Segmented legs present. One tarsal claw per leg. Usually with 3 tails (sometimes 2).
Mandibular tusks absent. Gills on abdominal segment 1 with single or double lamellae (plates) or forked. Gills on segments 2–7 double-layered lamellate (plate-like) and terminated in filaments or points and without fringe, or oval with fringe.
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