Rare Species Guide

 Agapetus tomus    Ross, 1941

A Caddisfly 

MN Status:
special concern
Federal Status:


(Mouse over a habitat for definition)

Minnesota range map
Map Interpretation
North American range map
Map Interpretation

  Basis for Listing

Agapetus tomus (a species of caddisfly) was first known in Minnesota from five specimens collected at a single Pine County location in 1963 (Mille Lacs Uplands).  More recently (2000-2002), there were 195 specimens collected from several localities in the eastern-central portion of the state, including near the original collection site in Pine County (Hardwood Hills and Mille Lacs Uplands subsections).  It is not clear why A. tomus is geographically restricted to such an enigmatic distribution in Minnesota yet is locally abundant at some of these sites. The species has a widespread distribution in the southeastern United States and has also recently been collected from a few sites in Michigan and Wisconsin. Further inventory work is needed to find additional populations of this species and delineate its full range in Minnesota.  Agapetus tomus was listed as a special concern species in Minnesota in 1996.


Caddisfly species can only be identified by examining their abdominal processes under a microscope. Houghton (2012) has developed an identification manual and key to Minnesota caddisfly species. Macroscopically, adults of A. tomus have light brown wings and are about 6 mm (0.24 in.) long. Larvae of A. tomus are unknown, but larvae of the genus typically range 5-7 mm (0.20-0.28 in.) long and construct cases of small rocks that superficially resemble tortoise shells (Wiggins 1996).


This species has not been positively correlated with its natal microhabitat. Agapetus larvae are typically found on exposed rock surfaces of fast-moving areas of clean, cold streams (Wiggins 1996). The Pine County site is near several small streams as well as the Snake and Kettle rivers. A site in  Charles Lindberg State Park  is located at a medium-sized stream that flows through a variety of agricultural and forested lands. The portion of this stream where the 2000 collection was made appears fairly undisturbed as it flows through the park.

  Biology / Life History

Collections of A. tomus adults in Minnesota have occurred in late June and mid-July. Larvae have not been collected but likely reach peak maturity in late spring. No specific life history data are known for this species beyond its collection date, but larvae likely feed on epilithic algae, diatoms, and particulate organic matter (Wiggins 1996).

  Conservation / Management

No specific conservation measures or management strategies can be developed for this species until the larval habitat is confirmed. However, Agapetus larvae are some of the least tolerant of caddisflies to anthropogenic disturbances such as warming water temperature, increased siltation, organic pollution, and changes in stream flow (Hilsenhoff 1987; Wiggins 1996; Barbour et al. 1999).

  Conservation Efforts in Minnesota

Field surveys in conjunction with a University of Minnesota study on the Caddisflies of Minnesota (Houghton et al. 2001), have been conducted to search for additional populations of this species, and an identification manual and key to Minnesota caddisflies has been developed (Houghton 2012).

  References and Additional Information

Barbour, M. T., J. Gerritsen, B. D. Snyder, and J. B. Stribling. 1999. Rapid bioassessment protocols for use in wadeable streams and rivers: periphyton, benthic macroinvertebrates, and fish, Second edition. EPA 841-B-99-002. United States Environmental Protection Agency, Office of Water, Washington, D.C.

Hilsenhoff, W. L. 1987. An improved biotic index of organic stream pollution. Great Lakes Entomologist 20:31-39.

Houghton, David C. 2012. Biological diversity of the Minnesota caddisflies (Insecta, Trichoptera). ZooKeys 189:1-389.

Houghton, D. C., and R. W. Holzenthal. 2003. Updated conservation status of protected Minnesota caddisflies. The Great Lakes Entomologist 36(1-2):35-40.

Houghton, D. C., R. E. Dewalt, A. J. Pytel, C. M. Brandin, S. E. Rogers, D. E. Ruiter, E. Bright, P. L. Hudson, and B. J. Armitage. In press. Updated checklist of the Michigan (USA) caddisflies, with regional and habitat affinities. Zoosymposia.

Houghton, D. C., R. W. Holzenthal, M. P. Monson, and D. B. MacLean. 2001. Updated checklist of the Minnesota caddisflies (Trichoptera) with geographic affinities. Transactions of the American Entomological Society 127(4):495-512.

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.

Monson, M. P. 1994. The caddisflies (Insecta: Trichoptera) of the Lake Itasca region, Minnesota, and a preliminary assessment of the conservation status of Minnesota Trichoptera. Thesis, University of Minnesota, Saint Paul, Minnesota. 135 pp.

Wiggins, G. B. 1996. Larvae of the North American caddisfly genera (Trichoptera), Second edition. University of Toronto Press, Ontario, Canada. 457 pp.

Back to top