Goera stylata Ross, 1938
Basis for Listing
Despite extensive, recent sampling throughout the state, Goera stylata (a species of caddisfly) is known in Minnesota from only three locations in the northern part of the state (Laurentian Mixed Forest Province): LaSalle Creek, Hubbard County; Nett Lake River, Koochiching County; and Fawn Creek, St. Louis County. It is more common in the eastern United States, thus, the LaSalle Creek population in Hubbard County may constitute the westernmost extent of the species’ range. Due to the known sensitivity of this species to disturbance and the few documented locations in Minnesota, Goera stylata was listed as a threatened species in Minnesota in 2013.
Mature larvae of G. stylata are around 15 mm (0.6 in.) in length. Larvae are brown in color with darker spots on the head and thorax. The first and second segments of the thorax have forward-facing projections on either side, lending the species a distinct appearance. Larval cases are composed of small rock fragments with larger pebbles on each side serving as ballast. Adults are light brown in color and 6-8 mm (0.2-0.3 in.) in length; males are smaller than females. Both genders are nondescript and can be confused with many other caddisfly species. 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 G. stylata in Minnesota. Species of Goera typically inhabit fast-moving, cold, clear streams where they feed on epiphytic algae that grows on the surfaces of stream rocks. They tend to be stenothermic and very sensitive to changes in water clarity and flow regime; LaSalle Creek is an undisturbed sand-bottomed stream flowing from LaSalle Lake to the Mississippi River.
Biology / Life History
Little is known about the life cycle of G. stylata in Minnesota. Adults have been collected in June and November; one larval specimen was collected in October. Larvae probably spend a year under the water consuming epiphytic algae before emerging as winged adults. This is in contrast to a northern Lower Michigan population where peak emergence of adults was in late May to early June and nearly all adults were gone by mid-June
Conservation / Management
Further research is necessary to identify any additional populations of the species as well as its specific habitat needs. The LaSalle Creek population seems fairly well-protected within the confines of Itasca State Park. Any future development of the riparian corridor or any changes that would decrease water quality or increase water temperature should be approached cautiously to preserve this disjunct population.
References and Additional Information
Coffman, W. P., K. W. Cummins, and J. C. Wuycheck. 1971. Energy flow in a woodland stream ecosystem: I. Tissue support trophic structure of the autumnal community. Archv fur Hydrobiologie 68(2):232-276.
Flint, O. S. 1960. Taxonomy and biology of some Nearctic limnephilid larvae (Trichoptera), with special reference to species in eastern United States. Dissertation. Cornell University, Ithaca, New York.
Houghton, David C. 2012. Biological diversity of the Minnesota caddisflies (Insecta, Trichoptera). ZooKeys 189:1-389.
Houghton D. C., C. M. Brandin, and K. A. Brakel. 2011. Analysis of the caddisflies (Trichoptera) of the Ministee River watershed, Michigan. Great Lakes Entomologist 44(1):1-15.
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.
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.