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In Search of the Elusive Northern Forestfly

By Candace Fallon on 4. August 2022
Candace Fallon
Surrounded my mountains, Emilie Blevins searches the surface of some late season snowpack for adults of the northern forestfly.
Xerces conservation biologist Emilie Blevins searches the surface of some late season snowpack for adults of the northern forestfly. (Photo: Candace Fallon/Xerces Society)


It is late August, and I’m climbing down from a small peak in northern Washington as snow swirls around me. My fingers, toes, and limbs are all numb. Every now and then I can see Canada just on the other side of the ridgeline, before the mist closes in again. Not ideal, I think to myself. Not ideal. 

My coworker and I pick our way down the rocky trail, back towards a small creek we had spotted earlier in the day. We’re here in the North Cascades looking for a creature that has often felt like the proverbial needle in a haystack – the enigmatic northern forestfly, Lednia borealis.

While the name is a bit of a misnomer – it is found primarily above the treeline – the northern forestfly is a species of stonefly that is classified as a Species of Greatest Conservation Need in the state of Washington. Working in partnership with the U.S. Forest Service and Washington Department of Fish and Wildlife, my colleagues and I have spent some time nearly every summer of the last seven years searching for this species and several other aquatic insects of conservation concern in alpine regions of the state. Our primary goal is to determine where these species occur, but we’re also interested in the overall community composition of the water bodies in which they’re found, and what habitat features might be important to their survival. 


Emilie Blevins sits beside a rocky stream in the mountains
Alpine stoneflies can be found in and around a variety of aquatic habitats, from glacier-fed creeks like the one seen above to small hillside seeps or even snow surfaces. (Photo: Candace Fallon)


Stoneflies play an important role in alpine ecosystems

If you’re unfamiliar with stoneflies, these are insects that spend the majority of their lives underwater, where they feed on other invertebrates, submerged leaves, or benthic algae. Adults are terrestrial, active for a short period in which their main focus is reproduction. In high elevation environments, stoneflies serve as food for other species, including birds, and play integral roles in nutrient cycling, since species that eat algae and other plant matter convert the nutrients captured in primary production into a valuable food source. Like many freshwater invertebrates, they are threatened by habitat loss, pollution, and climate change. Cold-adapted alpine species like the northern forestfly are particularly threatened by extinction due to their patchy distributions, limited dispersal abilities, and reliance on cold water habitats.


A small meltwater stonefly rests on someone's finger
The closely related meltwater stonefly, Lednia tumana, is another cold-adapted species known from mountainous areas of Montana and Alberta, Canada. It was recently listed as a threatened species under the US Endangered Species Act due to climate change-induced habitat loss. (Photo: Glacier NPS/Flickr)


Climate change threatens alpine ecosystems

Climate change is a growing threat to high elevation species, dramatically altering alpine ecosystems as glaciers recede and annual snowfall levels decline. For animals like the northern forestfly that live in snowmelt and glacier-fed streams, the rapid loss of meltwater sources has pretty clear and dire implications. In the Skagit River watershed alone – which is located in the North Cascades and is home to a number of northern forestfly populations and the most extensive glacial cover of any U.S. basin outside of Alaska – this decline has translated to a 25% reduction in meltwater in the last 50 years.


A Xerces conservation biologist hikes down from a small glacier that is now mostly just a snowfield. A chain of meltwater lakes can be seen in the distance, with smoke from nearby wildfires on the horizon.
The climate crisis is changing our alpine environments. Across the West, glaciers are receding and mountainous regions are receiving less and less snowfall. Here, a Xerces conservation biologist hikes down from a small glacier that is now mostly just a snowfield. A chain of meltwater lakes can be seen in the distance, with smoke from nearby wildfires on the horizon. (Photo: Candace Fallon)


Surveys discover new populations of rare stonefly

What does this mean for species like the northern forestfly? The overall picture looks grim, but recent research and our own findings have given us some reasons to be hopeful. For one, the increased survey efforts that Xerces and our partners have undertaken over the last few years have resulted in a larger than previously known range and distribution of this species, which is heartening. Prior to the start of our survey efforts in 2015, Lednia borealis had been documented from just nine sites in northern Washington. We were curious if the species was found throughout the Cascades, but surveys throughout the southern and central parts of the range have proven largely unfruitful – despite surveying over 60 sites over a three year period, we did not detect a single individual.

Yet as we moved north, our success improved. We had our first positive detections in 2018 at two sites in the Glacier Peak Wilderness, and since then we have found Lednia borealis at multiple sites in the North Cascades, including several places that had not been surveyed since the 1980s. The species is now known to occur in at least 23 sites in Washington and is likely found in even more. 


Northern forestflies depend on meltwater from snow and glaciers. Adults can be found on rocks and vegetation adjacent to creeks and streams, and even on snow surfaces. In 2019, Xerces biologists confirmed that the species was extant at multiple sites on Mt. Baker. (Photo: Candace Fallon).


The extent of potential habitat for the northern forestfly has also grown. Because we have been incorporating genetic barcoding into our work, we’ve had some unexpected findings, including the revelation that the northern forestfly appears to occur in the mountains of British Columbia, Canada – approximately 600 km north of our Washington sites! Given the relatively extensive glacial habitat that still exists in that region of the world, it is very possible that these mountains could prove to be a stronghold for the species.

In the meantime, we will continue our efforts in Washington. The results from these surveys are already being used to help identify conservation priorities and management actions in Washington, and will be incorporated into the 2025 update of the State Wildlife Action Plan. Beyond contributing to ongoing regional efforts among partners, this work also provides much needed genetic data to barcoding libraries, forms a baseline for long term species and climate change monitoring, and expands our collective knowledge of the Lednia genus as a whole—and mountain stream biodiversity overall—in the West.


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Candace is a senior conservation biologist with the Xerces Society, where she works with researchers, land managers, and community scientists to study and protect at-risk invertebrates and their habitats. She has extensive experience with species inventories and monitoring, providing technical guidance to land managers, developing and managing community science projects, and conducting outreach. Much of her work has focused on conserving imperiled butterflies, beetles, mollusks, and aquatic macroinvertebrates on federal lands in the western U.S.

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