Insect found on Cache la Poudre River tributaries warrants protection under Endangered Species Act

The U.S. Fish and Wildlife Service announced today that the Arapahoe snowfly, an insect found in two tributaries of the Cache la Poudre River, warrants protection under the Endangered Species Act (ESA), but that proposing the species for protection is precluded by the need to address other higher priority species. The species will be added to the list of candidate species and its status will be reviewed annually.

The Service has completed a comprehensive status review — known as a 12-month finding — and determined that there is sufficient scientific and commercial data to propose listing the species as threatened or endangered throughout its range. However, due to limited resources devoted to other higher priority actions, the agency is precluded from beginning work immediately on a listing proposal.

“When a ‘warranted but precluded’ finding is made for a species, we classify it as a candidate for addition to the federal list of threatened and endangered species,” said Mike Thabault, Assistant Regional Director, Ecological Services. “If we propose the Arapahoe snowfly for protection under the ESA in the future, the public will have an opportunity to comment,” he stated.

The Arapahoe snowfly is a species of insect in the order Plecoptera (stonefly). Stoneflies, including the Arapahoe snowfly, are typically found in cold, clean, well-oxygenated streams and rivers. They are sensitive to most types of pollution.

The species was first discovered in 1986 in Young Gulch, a small tributary of the Cache la Poudre River in the Front Range of the Rocky Mountains of Colorado. It is a small, dark‑colored insect with both a body length and wing length of approximately 0.2 inches. In 1988, it was identified as a new species. It was also found in a second tributary, Elkhorn Creek, approximately five miles from Young Gulch. No other populations have been found in searches of nearby tributaries, and numerous visits to Young Gulch since the species’ discovery in 1986 have failed to locate additional specimens. Thus, the Service believes the species is extirpated from Young Gulch and currently only occurs in Elkhorn Creek.

The species has a complex one-year lifecycle that requires terrestrial habitat during its adult phase and aquatic habitat during immature phases. In late winter, adults emerge from beneath stream ice to mate. Females detach an egg mass onto the water and eggs hatch in early spring. As water temperatures rise, nymphs move into the stream substrate and undergo a period of inactivity during the warm months. As water temperatures drop in the late fall, nymphs complete their development into adults.

The status review identified threats to the species including the potential present and future threat of habitat modification caused by climate change; the lack of adequate regulatory mechanisms to protect the species from impacts due to climate change; and its small population size (only one known population with few individuals documented).

The U.S. Forest Service, which manages the lands where the Arapahoe snowfly has been located, oversees several other activities, including recreational use, forest management, and grazing, which were not found to be threatening the species at this time.

For more information about the Arapahoe snowfly and this finding, please visit the Service’s website at

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