Triaenodes flavescens    Banks, 1900

A Triaenode Caddisfly 

MN Status:
special concern
Federal Status:


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Minnesota range map
Map Interpretation
North American range map
Map Interpretation


Triaenodes borealis

  Basis for Listing

Triaenodes flavescens (a species of long-horned caddisfly) is more common in the eastern U.S., and the Minnesota populations may be near the western edge of its range. The species was known prior to 1950 from several sites in the northwestern third of the state (Prairie Parkland Province)  Recent extensive statewide sampling, however, has located it only from Sucker Brook in Clearwater County in late July 1988, and Devil Track Lake in Cook County in mid-August 1992 (Laurentian Mixed Forest Province). The apparent decrease in distribution of T. flavescens, especially in the northwestern portion of its Minnesota range, is alarming and likely due to habitat loss in this area, hence it was listed as a special concern species in 2013.


Mature larvae of T. flavescens are around 14 mm (0.55 in.) long. The head and thorax are pale yellow with prominent black stripes and spots. Larval cases are long, narrow, and tapered. They are composed of pieces of plant material arranged in a distinct spiral formation. Adults are 10–12 mm (0.39-0.47 in.) in length. They have bright yellow wings with a distinct darker pattern. Other Triaenodes have a similar pattern however, so specimens can be definitively identified only by a close examination of the terminal abdominal segments under a microscope. Houghton (2012) has developed an identification manual and key to the caddisflies of Minnesota.


Little is known about the specific habitat requirements of T. flavescens. Species of Triaenodes live in a variety of habitats and feed on living plant material. They are sensitive to disturbances of the riparian corridor. Sucker Brook is a slow-flowing, undisturbed, 2nd order stream.  Devil Track Lake is a large (1,868 acre, 50 ft. deep) lake.

  Biology / Life History

Little is known about the specific life cycle of T. flavescens. Larvae probably spend a year under the water consuming vascular plant tissue before emerging as winged adults in the summer. All recent adult specimens in Minnesota were caught from late July to mid-August.

  Conservation / Management

Little is known about the specific conservation needs of T. flavescens. Sucker Brook is fairly well-protected by the Iron Springs Bog Scientific and Natural Area.  Any future development of the riparian corridor of this stream or any changes that would decrease water quality or increase water temperature should be approached cautiously to preserve this isolated population of T. flavescens. Devil Track Lake lies within the Superior National Forest.  Further research is necessary to identify any additional populations of the species as well as its specific habitat needs.

  Conservation Efforts in Minnesota

No specific conservation efforts have been directed towards this species in Minnesota. However, the known population occurring in Sucker Brook within Iron Springs Bog Scientific and Natural Area is afforded the highest level of state environmental protection.