Arapahoe snowfly Capnia arapahoe
ESA status: candidate for listing

Arapahoe snowfly pc Boris Kondratieff

The Arapahoe snowfly has only been found in two tributaries of the Cache La Poudre River, west of Fort Collins, Colorado, and may have disappeared from one of them. The species was first identified in 1986. These tiny insects are called snowflies because they are adapted to winter conditions. The adults emerge in late winter or early spring, often when there is still snow on the ground.

The Arapahoe snowfly is a variety of stonefly, and like their relatives they require cold, clean, well-oxygenated streams. Stoneflies are very sensitive to declining water quality and are among the first macroinvertebrates to disappear from streams and rivers impacted by thermal or chemical pollution and habitat degradation. This probably explains why the Arapahoe snowfly is disappearing from its tributary habitats.

Elkhorn Creek and Young Gulch, the two tributaries where this rare insect is found, are both vulnerable to effects from heavy recreational use, drought, and other factors. Increasing impacts from a growing human population in the area pose myriad threats to the snowfly: sedimentation and runoff from foot and mountain bike traffic; water contamination from litter and pet waste; streambank trampling from camping, hiking, biking, and horseback riding; construction and maintenance of stream crossings and culverts which can interrupt streamflow; and erosion, runoff, and water withdrawal from development. Drought has affected streamflow in both tributaries. Finally, climate change could lead to warmer water temperatures, increased flooding in spring and drought in the summer, and ice melt earlier in the season, all of which could impact the snowfly.

The Arapahoe snowfly may already be extirpated from Young Gulch. The gulch is one of the most popular hiking destinations in the Cache la Poudre River Canyon. Tens of thousands of hikers, dogs, mountain bikers, horseback riders and campers pass through every year. Elkhorn Creek receives less use, but a new trailhead was completed there in 2010 and trail usage is expected to increase. The Forest Service has slated 14 existing stream crossings for improvement to prevent increased runoff and erosion.

With its naturally small population and limited range, it wouldn’t take much for the Arapahoe snowfly to vanish forever. This tiny insect is a barometer of river health. Protecting it would also protect the Cache La Poudre and all the species that live there. With help from Xerces Society and WildEarth Guardians, the snowfly is moving closer to the federal protections it needs, and we will continue to fight for its survival.

photo credit: Boris Kondratieff