Ochrotrichia spinosa (Ross, 1938)
A Purse Casemaker Caddisfly
Basis for Listing
Historically, Ochrotrichia spinosa (a species of purse casemaker caddisfly) is known from sporadic collections in both northern and southern Minnesota. Despite extensive statewide sampling, however, it has yet to be rediscovered from any of its historical Minnesota habitats. Since 1960, this species is known from only a single collection of five adult specimens. They were collected from Valley Creek at the Belwin Conservancy in Washington County (St. Paul-Baldwin Plains and Moraines Subsection) in July 2001. The species appears to be more common in Michigan and Wisconsin, and the Minnesota population appears to be near the western edge of the species’ range. Due to the few documented locations of this species and the vulnerability of its only known extant population, Ochrotrichia spinosa was listed as endangered in 2013.
The larva, specifically, of O. spinosa is unknown. Mature larvae of the genus Ochrotrichia are 4–5 mm (0.2 in.) in length. They have a cream-colored abdomen with a darker head and thorax. Immature larvae are free-living and do not build cases. Mature larval cases are composed of two silken valves covered with silt or small sand grains. Adults are 3–4 mm (0.1-0.2 in.) in length and are light brown in color. Macroscopically, they are indistinguishable from the several dozen other species of Hydroptilidae known from the state. Adults 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 needs of O. spinosa beyond the dependence of the larva on diatoms for their food source. Valley Creek is a small fast-flowing stream with some riparian protection from the surrounding Belwin Conservancy.
Biology / Life History
Little is known about the specific life cycle of O. spinosa. Larvae probably live for a year under the water feeding on diatoms from rock surfaces before emerging as winged adults during summer. In Minnesota, the only recent specimen of O. spinosa was collected in July.
Conservation / Management
Small fast-flowing streams appropriate for O. spinosa are very rare in east-central Minnesota and those that remain are under imminent threat of urban development. Valley Creek has some degree of habitat protection from the Belwin Conservancy. 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 O. spinosa. Further research is necessary to identify any additional populations of the species.