Ecological Role

Despite having an average lifespan that ranges from mere hours to a few days, it is not difficult to come across a colony of Isonychia bicolor mayflies, as their breeding grounds are widespread and they are quite an abundant species wherever they are found. Some research shows that they are very particular to which kinds of rivers they can successfully inhabit, but overall the population is large compared to other insects (Neuswanger 2012). (This is not to mention they have two generations per year, which contributes to their puzzling high prevalence. For more on this, see our page about Reproduction and Life Cycle!) While the genus Isonychia is able to thrive in habitats across the globe, with its members scattered even throughout parts of Asia and Central America, Isonychia bicolor  is distributed primarily on the North American continent (Kondratieff and Voshell 1984). Among the many places where it resides, the majority of the species inhabits the eastern region of the United States and occurs with highest concentration in swiftly-flowing, relatively large mountain rivers and streams (Kondratieff and Voshell 1984, Echols et al. 2010).

Most often, Isonychia bicolor is found most often in the Benthic zone** of these water bodies and tends to prefer areas where the vegetation is dense and twisted, and various debris of the woods (sticks, leaves, decaying organic matter) coats the water in a nutrient-rich layer (Echols et al. 2010).

**The Benthic zone, for clarification, skirts the floor all the way down to the bottom, across, and back up again on the other side of bodies of water, including riverbeds. This organism, in its early life stages, spends most of its time in the uppermost part of this zone--that is, the segment that rests closest to the land of the shoreline/river's edge.

Feeding Habits/Nutrition:
Isonychia bicolor is one of four Isonychiidae ("brush-legged") genera in North America that utilize the technique called "suspension" or "filter" feeding to gain 98% of their nutrients from "amorphous detritus" in rivers and streams. These organic debris particles are generally generally ranging from 0.1-0.7 micrometers, or μm in size (Echols et al. 2010).

Clinging on to rocky riverbed substrates, these "streamlined, vigorous swimmers" face the direction of the current, using tiny appendages called setae on their fore- (front) legs as a kind of self-created, evolutionarily-produced, makeshift fishing net (Echols et al. 2010). It is using this evolutionary technique that they are able to collect the fine particles they do, creating a mutually beneficial exchange between themselves, who receive a hearty meal, and their neighboring species, who enjoy cleaner water as a result of the straining action of Isonychia bicolor setae at work (Jacobi and Benke 1991).

Only the larval (nymph) forms of these mayflies feed at all; strangely enough, once they have developed into their adult forms, the parts of their entire system have vanished—mouthparts and all (Net Industries 2012)! To see more on life cycle stages, click here.

These mayflies also obtain food by scraping algae from rocks and sediments, and by consuming diatoms, and decomposing plant material. In some habitats they consume plankton and smaller aquatic insects by way of predatory behavior, which is quite rare among the mayfly genera (Neuswanger 2012; Net Industries 2012).

Environment/Other Species Interactions:

Because Isonychia bicolor  cleans the water in which they live, they can be considered the custodians of the currents (Jacobi and Benke

Because they can consume a variety of food sources, Isonychia bicolor allow for more different species to live in the same habitat.

Isonychia bicolor and Us: Scientific, Economic, Practical and Commercial Uses:

The nymphs of Isonychia bicolor are especially desirable for the study of ecotoxicology, a domain of ecology concerned with protecting ecosystems and their inhabitants by optimizing environmental conditions. Why?

    - Nymphs are very sensitive to pollutants, serve as good indicators of contamination like some types of metal, ammonia, etc.

   - Researchers use these nymphs in field studies to identify sources of pollution and identify its environmental  impact (Echols et al. 2010).

Another large use of these mayflies which pertains to many, many people, especially those who consider themselves native to the northwoods country, is the popular hobby/"sport" of fly-fishing. Whether for recreation, for food, for the industry itself, or for the simple love of harnessing nature by the river, the Isonychia bicolor insect in all of its forms makes a great lure for trout and more.

        -For more information on commercial fly-fishing and the species involved with it, view the photo- and blog-filled homepages of these two avid naturists, researchers, photographers, lovers of the outdoors, and proclaimed fisher-people themselves at:
                                Jason Neuswanger (, and
                                Nome Buckman (



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