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Montana Field Guide

Montana Field Guides

A Rhyacophilan Caddisfly - Rhyacophila newelli

Species of Concern

Global Rank: G2
State Rank: S2
* (see State Rank Reason below)

Agency Status
USFWS:
USFS:
BLM:


 

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State Rank Reason (see State Rank above)
This Rhyacophilan Caddisfly is currently ranked a "S2" Species of Concern in MT at risk because of very limited and/or potentially declining population numbers, range and/or habitat, making it vulnerable to extirpation in the state. Limited sites with small populations, but also difficult to identify without adult specimens.
 
General Description
Rhyacophila newelli is a free-living caddisfly (no case) that is a regional endemic only known to occur in Montana, Alberta, and British Columbia (Wiggins 1996, NatureServe 2015). Distribution and ecological data for the United States and Canadian provinces is known to be incomplete or has not been reviewed for this taxon. Although, given it's locality information for Montana, this species like others in the Angelita species group, prefer small, fast-flowing cold forested streams.

Diagnostic Characteristics
See Denning 1971 for detailed adult description. Larval body length is 12-15 mm. Head usually wedge-shaped with patterning, no gills on the abdominal segments, apical extension off of the anal claw present. This species is a member of the angelita species group and cannot be separated as larvae from 2 other species that occur in Montana (see photo).

Range Comments
Rangewide, Rhyacophila newelli is a regional endemic only known to occur in Montana (Newell and Potter 1973), Alberta, and British Columbia (Wiggins 1996, NatureServe 2015). Distribution data for United States and Canadian provinces is known to be incomplete or has not been reviewed for this taxon. Known from Rattlesnake Creek, Missoula Co., Montana (Newell and Potter 1973); also in Alberta. It is unclear how a distribution map would look given the limited knowledge.

Summary of Observations Submitted for Montana
Number of Observations: 1

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density

Recency

 

(Observations spanning multiple months or years are excluded from time charts)



Habitat
This species is associated with high gradient, perennially flowing headwater springs and streams (Wiggins 1996). These caddisfly larvae are free-living and move actively searching for food (predatory) with no case, until just before pupation. The trophic relationship of Rhyachophila is usually predatory on other insects, especially chironomids (midge larvae) and simulids (blackfly larvae) (Merritt and Cummins 1996).

Food Habits
Most Rhyacophila species are free-living predators feeding mostly on aquatic insects, especially midges and blackflies.

Ecology
This species, like others in the angelita species group, prefer small, fast-flowing cold forested streams.

Reproductive Characteristics
Adults were collected in mid-July (Denning 1971), other than that not much is known of this species.

Management
Limited data and the inability to identify larval collections has lead to a low global rank. Distribution data for United States and Canadian provinces is known to be incomplete or has not been reviewed for this taxon.

Threats or Limiting Factors
Specific threats to Montana populations of R. newelli would include mismanagement of forested riparian areas, including sediment and temperature increases associated with road building and timber harvests not following BMPs. In general, cold-stenothermic (cold-water specialists) invertebrate populations are affected by changes to aquatic habitat, such as alteration of flow patterns, streambed substrate, thermal characteristics, and water quality. Alteration and degradation of riparian and aquatic habitat is the primary concern for Montana populations.

References
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Citation for data on this website:
A Rhyacophilan Caddisfly — Rhyacophila newelli.  Montana Field Guide.  .  Retrieved on , from