Headwaters chilostigman caddisfly adults are small, moth-like insects 0.3 to 0.4 inches long that are active in winter. They have semi-translucent, pale brown wings sporting a sprinkling of darker brown spots and patches; the body and appendages are darker brown. Several similar caddisfly species are difficult to identify in the field, but the headwaters chilostigman caddisfly's habitat and its midwinter activity are helpful clues to its identity.The immature stages are unknown; however, unidentified larval specimens collected in Itasca State Park may prove to be this species.
This species is primarily a denizen of black spruce, tamarack, and white cedar swamps and fen openings in northern Minnesota. Among its haunts are the large patterned peatlands of the Glacial Lake Agassiz region. It can occasionally be found in sedge meadows. Within these wetlands, populations are found in seepages or areas of subtle water flow. Adults sometimes wander out of these areas into nearby habitats, including upland forests. Deep snow covers these habitats when the adults are active.
Biology and Life History.
Despite being a cold-blooded invertebrate, the headwaters chilostigman caddisfly is remarkably at home in frozen winter landscapes. Like many cold-weather insects, it likely derives its hardiness from chemicals that keep its blood-like hemolymph from freezing. Adults scurry over the snow surface on sunny days when temperatures rise above freezing. They do not appear to fly, but may glide when leaping from a snowy ledge. They are most often seen in January and February but can persist into March. Adults appear to finish their lives before the spring ice breakup period, when other caddisfly species may be found on the snow. Adults are not known to feed. Although the immature stages are unknown, related species feed on leaf litter, other vegetation, and microorganisms.
History and Status.
This enigmatic insect was first discovered in Itasca State Park in 1974, and would continue to be known from this sole location—worldwide—for the next 31 years. During this period it was listed as endangered in Minnesota to protect the only known population. New discoveries in 2005 and 2011 led to a new listing as threatened. In February 2017, the Minnesota Biological Survey found the species in three more locations in far northwestern Minnesota.
These discoveries suggest that the species is more widespread than previously thought, and that several large northern peatlands support robust populations. Additional surveys are needed to learn more about this species' distribution and habitat needs. If you are out snowshoeing or snowmobiling in northern Minnesota, keep an eye out for this elusive insect.
Kyle Johnson,, DNR zoologist, Minnesota Biological Survey