Distinguishing characteristics - Larvae of the brushlegged mayflies have a minnow-like (Fig. A) appearance when they swim. Their gills have fibrils shorter than their gill plates (Fig. B). The best feature for distinguishing them is the double row of long setae on the inner margins of their femora and tibiae of fore legs (Fig. C) from which they get their name. Their gills on segment 1 are dorsolateral and platelike. Other gills are also platelike (Fig. D).
The Family Isonychiidae has only one genera, Isonychia, which has 17 species. It is common and widespread across the United States. They are active swimmers that swim into brisk currents and filter algae and diatoms from the water using the long setae on their fore legs. They may also eat other, smaller, nymphs or larvae. Isonychia are noted for having both primitive features (primitive trachea) and specialized features (feeding apparatus).
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Genus - Isonychia
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Tolerance Value - 2
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Feeding Group - Collector
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Notes - Isonychia are found in flowing water. They are generally swimmers and/or clingers. Generally they are collecting (filtering), although some species are predators (engulfers). The size of the Brushlegged Mayflies larvae at the largest stage is 8-17 mm excluding tail.
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