Ylodes frontalis (Banks, 1907)
Basis for Listing
Ylodes frontalis (a species of long-horned caddisfly) is common in the northwestern United States and into Canada and Alaska; it appears to be on the edge of its range in Minnesota. The species is known from only two collections of adult specimens in the western third of the state: Signalness Lake, Pope County (Minnesota River Prairie Subsection) in 1972; and Hayes Lake, Roseau County (Agassiz Lowlands Subsection) in 1999. The two sites are separated by over 300 km (185 mi.). Lakes in the western portion of Minnesota have been degraded over the last few decades by agricultural development leading to the detriment of many species including this one. Ylodes frontalis was listed as a threatened species in Minnesota in 2013.
Mature Y. frontalis larvae are 10–12 mm (0.39-0.47 in.) in length. The head and thorax are pale yellow with darker blotches. Larvae of Ylodes are very similar to those of Triaenodes, and they are sometimes considered a single genus. Larval cases are tubular, thin, and tapered. They are composed of small pieces of plant material arranged in a spiral formation. Adult Y. frontalis are 10–12 mm (0.39-0.47 in.) in length with nondescript grey wings. They look similar to many other species of Leptoceridae (long-horned caddisflies). 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.
The specific habitat needs of Y. frontalis are unknown. Ylodes larvae live in the shallow areas of lakes within dense beds of aquatic plants where they feed on plant material. Hayes Lake is a mesotrophic lake with some watershed protection from Hayes Lake State Park. Signalness Lake is a small shallow lake that is regularly stocked for fishing, and it is afforded some watershed protection from Glacial Lakes State Park.
Biology / Life History
Little is known about the specific life cycle of Y. frontalis. Larvae probably spend a year under the water consuming vascular plant tissue before emerging as winged adults in the summer. All adult specimens in Minnesota were caught in late August.
Conservation / Management
Little is known about the specific conservation needs of Y. frontalis. Undisturbed lake habitats in western Minnesota are rare and so protection of remaining habitats is critical. Currently, the state parks seem to provide habitat protection for the species. Any future development of the watersheds of Hayes Lake or Signalness Lake or any changes that would decrease water quality or increase water temperature should be approached cautiously to preserve these isolated populations of Y. frontalis. Further research is necessary to identify any additional populations of the species as well as its specific habitat needs.