Limnephilus janus Ross, 1938
Basis for Listing
Until recently, Limnephilus janus (a species of northern caddisfly) was known in Minnesota from only a single specimen collected in 1965 from Hubbard County (Chippewa Plains). Then, in 2000, during an extensive, statewide sampling effort, an additional specimen was collected from Little Elbow Creek in Mahnomen County (Pine Moraines & Outwash Plains) confirming the extant status of the species within Minnesota. The species is more common in the western U.S., though specimens have been recently collected from Michigan as well. The Minnesota population is likely isolated from other populations of L. janus. Due to its few documented locations in Minnesota, its sensitivity to riparian disturbance, and the vulnerability of its habitats, Limnephilus janus was listed as an endangered species in 2013.
The larva, specifically, of L. janus is unknown. Mature larvae of the genus Limnephilus range 20-30 mm (0.8-1.2in.) in length. They are variable in coloration. Larval cases can be composed of wood pieces, pebbles, or leaves. Adults of L. janus are 16-18 mm (0.63-0.71 in.) in length; females are larger than males. Both genders are light brown in color without patterning on the wings. Specimens can be definitively identified only by a close examination of the terminal abdominal segments under a microscope. They are very difficult to distinguish from the 18 other Limnephilus species known from Minnesota. Houghton (2012) has developed an identification manual and key to the caddisflies of Minnesota.
Little is known about the specific habitat requirements of L. janus. Most limnephilid caddisfly species tend to be intolerant of habitat disturbance, especially that of the riparian zone since they depend on terrestrial input for their food source and case-building materials. Little Elbow Creek is an undisturbed, low-gradient outlet of Little Elbow Lake.
Biology / Life History
Little is known about the specific life cycle of L. janus in Minnesota. Larvae probably spend a year under the water consuming detritus and other organic matter. Both adult specimens from Minnesota were caught in July.
Conservation / Management
Little Elbow Creek has some degree of current habitat protection by the surrounding state forest land. 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 isolated populations of L. janus. At the very least, establishing riparian buffer zones between human disturbance and L. janus habitat would probably benefit the species. Further research is necessary to identify any additional populations of the L janus as well as its specific habitat needs.
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
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. 2007. The effects of landscape-level disturbance on the composition of Minnesota caddisfly (Insecta: Trichoptera) trophic functional groups: evidence for ecosystem homogenization. Environmental Monitoring and Assessment 135(1-3):253-264.
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.
Ruiter, D. E. 1995. The adult Limnephilus Leach (Trichoptera: Limnephilidae) of the New World. Ohio Biological Survey Bulletin, New Series, 11: 1-200.
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.