Holocentropus milaca    Etnier, 1968

A Caddisfly 

MN Status:
(as Polycentropus milaca)
Federal Status:


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Minnesota range map
Map Interpretation
North American range map
Map Interpretation

  Basis for Listing

When assigned special concern status in 1996, the extant status of Holocentropus milaca (a tube casemaker caddisfly) had not been confirmed.  In fact, the species was known worldwide from only a single specimen collected in 1965 from a seepage lake in Itasca County.  In 2000, two very small populations were discovered at seepage lakes in Cass County.  Despite extensive sampling of aquatic habitats throughout Minnesota, H. milaca has not been found anywhere else within the state.  These three populations (all located within the Northern Minnesota Drift and Lake Plains Section) and a single population in Michigan are the only known populations of H. milaca worldwide. Due to the few known locations and the sensitivity of its habitat, this species’ status was elevated to endangered in 2013.


Caddisfly species can only be identified by examining their abdominal processes under a microscope. The Holocentropus species of North America can be identified using Armitage and Hamilton (1990). Houghton (2012) has developed an identification manual and key to Minnesota caddisflies. Macroscopically, adult males of H. milaca are about 9 mm (0.35 in.) long and have light brown wings. Larvae and females, specifically, of H. milaca are unknown.


Holocentropus milaca has not been positively correlated with its natal microhabitat. Larvae of the genus Holocentropus are found in both lakes and streams (Wiggins 1996). All three localities from which adults of H. milaca have been collected in Minnesota are small oligo- to mesotrophic seepage lakes.

  Biology / Life History

All collections of H. milaca adults have occurred between late June and mid-July. No other specific life history data are known for this species. Larvae of H. milaca have not been collected but likely reach peak maturity in late spring and early summer.  Larvae of the genus are commonly predacious and live in silken tubes on the undersides of rocks (Wiggins 1996).

  Conservation / Management

No specific conservation measures or management strategies can be developed for this species until the larval habitat is confirmed. Few data are available on general Holocentropus tolerance to anthropogenic disturbances.

  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

Armitage, B. J. and S. W. Hamilton. 1990. Diagnostic atlas of the North American caddisfly adults. II. Ecnomidae, Polycentropodidae, Psychmoyiidae, and Xiphocentronidae. The Caddis Press, Athens, Alabama (Columbus Ohio). 152 pp.

Etnier, D. A. 1968. Range extensions of Trichoptera into Minnesota, with descriptions of two new species. Entomological News. Vol 79, pp. 188-192.

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

Houghton, D. C. 2002. Biodiversity of Minnesota caddisflies (Insecta: Trichoptera). PhD Thesis, University of Minnesota, Minneapolis, Minnesota. 194 pp.

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.

Leonard, J. W., and F. A. Leonard. 1949. Noteworthy records of caddisflies from Michigan, with descriptions of new species. University of Michigan Museum of Zoology Occasional Papers 520, Ann Arbor.

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.

University of Minnesota Department of Entomology Insect Collection. 2009. UMSP Trichoptera: caddisflies. University of Minnesota, St. Paul. <http://www.entomology.umn.edu/museum/databases/>. Accessed 05 August 2009.

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

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