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Neothremma andersoni adults are 5 to 6 mm in length, with the body and appendages medium brown in color. Male N. andersoni differ in having enlarged scale-hairs along the major veins (basally on the forewings and centrally on the hindwings). Identification often requires close examination of adult male genitalia or mature male pupae.
This species occurs only in small streams in the Columbia Gorge. Neothremma andersoni relies on spring-fed systems that have stable, cooler temperatures, and relatively high humidity. Elevations of known populations along Wahkeena Creek range from around 55 to 472 m (180 to 1,550 ft.). Larvae and pupae prefer moderate to high gradient stream reaches, above the gorge escarpment, and fewer are found as the stream flows out onto the Columbia River floodplain. Within the creek, the larvae of this species are associated with cobble, rubble, and bole wood substrates and are most abundant in shallow, margin habitats with moderate current. They are not found in torrential waters, or in accumulation of fine sediments or detritus. Adults of this species are found near the stream on understory vegetation and on rocks and logs protruding from the stream or its margin.
Limiting factors
This Columbia Gorge endemic has a narrow distribution and may be especially vulnerable to changes in water quality and flow. This species is threatened by trampling caused by recreational activities and temperature increases due to climate change, as this species is adapted to cold water systems. Pollution (e.g., sedimentation, eutrophication, and chemical) caused by road construction and impervious surface run-off could impact this species. Sedimentation and bank erosion from heavy recreational activity, landslides, and wildfires could also impact this species.
Data gaps
Collect life history and population data. Determine species-specific habitat requirements. Assess distribution. Measure abundance within the correct sampling season. Conduct demographic studies. Investigate vulnerability to environmental threats.
Conservation actions
Monitor known populations and survey suitable habitat for new populations. Maintain stream water quality and sediment regimes. Use eDNA sampling analysis to determine species presence.
Key reference or plan
Hietala-Henschell, K., S. Foltz Jordan, S. Jepsen, and E. Scheuering. 2020. Interagency Special Status/Sensitive Species Program (ISSSSP) Species Fact Sheet:Â Neothremma andersoni. USDA Forest Service Region 6 and USDI Bureau of Land Management Oregon State Office. 22 pp.
