Chilostigma itascae Wiggins, 1975
Headwaters Chilostigman Caddisfly
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Basis for Listing
Until recently, the Headwaters Chilostigman Caddisfly (Chilostigma itascae) was known world-wide from less than ten specimens collected in 1974 and 1995 from Itasca State Park in north central Minnesota (Pine Moraines & Outwash Plains Subsection). This endemic species was listed as endangered in Minnesota in 1996 to ensure that the only known extant population was protected from extinction.
In 2005, a large and extensive population was discovered in the Sand Lake Peatland Scientific and Natural Area in Lake County (Laurentian Uplands Subsection), and in 2011 another population was found in Hubbard County. In light of these new discoveries, the status of C. itascae was changed to threatened in 2013.
In 2017, the Headwaters Chilostigman Caddisfly was discovered at three more locations in northwestern Minnesota (Agassiz Lowlands Subsection) as well as just over the border into southeastern Manitoba.
Only two species of Chilostigma are known worldwide: the Minnesota endemic C. itascae, and the Scandinavian C. sieboldi. Caddisfly species can only be identified by examining their abdominal processes under a microscope. Houghton (2012) has developed an identification manual and key to Minnesota caddisfly species. Macroscopically, adult Headwaters Chilostigman Caddisflies are 8-10 mm (0.31-0.39 in.) in length with brown wings bearing black hairs. Larvae of the genus Chilostigma are unknown, though two unusual limnephilid larvae were collected in August of 1974 from Itasca State Park and subsequently described as "likely candidates" for Headwaters Chilostigman Caddisfly larvae (Wiggins 1996). An intense effort to find and positively correlate Headwaters Chilostigman Caddisfly larvae through rearing to adulthood was unsuccessful (Holzenthal et al. 1997).
The location where the Headwaters Chilostigman Caddisfly was first discovered is a small meandering, silt-bottomed stream that flows through a wet meadow/carr with several spring seeps. It was from these spring seepage areas that possible larvae were found and described (Wiggins 1996). The Hubbard County locality is comprised of northern rich tamarack swamp and wet meadow/carr surrounding a lake; numerous seepage areas are present as well. Three of the other Minnesota localities, as well as the Manitoba locality, are large peatland complexes. Within these complexes, most observations have been in northern rich spruce swamp, though they have also been observed in northern poor fen, northern poor conifer swamp, northern rich tamarack swamp (water track), and northern extremely rich fen in spring fen channels (a type of patterned peatland). Seepage areas (analogous to those mentioned above) are present near some of the observations, though they are typically hidden by deep snow when the adults are active. The adults can apparently wander a considerable distance from their larval habitats as they have been found in upland forest habitats on two occasions (one documented locality is based solely on such an encounter). This complicates identification of the precise larval microhabitats, though it seems logical that seepages, wet hollows, and other areas of concentrated water flow in peatlands are most likely.
Biology / Life History
Adults are usually seen walking rapidly on the snow surface during warm winter days when temperatures are at or above freezing. Unlike most caddisflies, C. itascae does not appear to fly, however, one was observed expanding its wings while leaping down from a snowy ledge (Kyle Johnson, pers. obs.). Most observations have been from late morning to early afternoon with full or partial sun. They have been collected February through March, however, the Scandinavian C. sieboldi adults are found on snow during late fall and early spring (Schmid 1952) so it is possible that C. itascae could be as well. More field work is needed to determine adult phenology and activity patterns.
Definitively identified larvae have not been collected, so it is unknown when mature larvae are present. The species’ unusual winter emergence could be the result of larvae maturing and pupating in late summer or fall and delaying emergence until late winter; or it could be that the larvae do not mature and pupate until sometime in winter. The species may take several years to develop from egg to adult as evidenced by the failure to detect any adults prior to the 1995 observations despite a rigorous collecting effort by Monson (1994) between 1988 and 1993 including year-round adult emergence trapping from January 1988 to June 1990. Another possible explanation is that the precise conditions for adult emergence are infrequent, and the species remains in the pupal stage until such an event comes along.
The species’ dietary needs are unknown, however, species of related genera generally consume woody debris and microorganisms (Wiggins 1996).
Conservation / Management
Maintenance of wetland hydrology is undoubtedly critical for survival of this species, though no specific conservation measures or management strategies can be developed until larval microhabitats are better known. No data are available on general Chilostigma tolerance to anthropogenic disturbances. Larvae of related genera tend to be intolerant of organic pollution, modification of riparian habitat, and warming water temperature (Harris and Lawrence 1978; Hilsenhoff 1987; Wiggins 1996; Barbour et al. 1999). The Itasca State Park population of the Headwaters Chilostigman Caddisfly appears to be very small and on that basis alone vulnerable to extirpation.
Conservation Efforts in Minnesota
Most known localities of the Headwaters Chilostigman Caddisfly are within publicly owned lands managed for natural resource values. The Itasca State Park locality is safe from intentional, acute, habitat destruction, though Monson (1994) recommended that the site and its surrounding wetland meadow be monitored for signs of watershed-level habitat degradation. The three largest populations (Sand Lake Peatland, Mulligan Lake Peatland, and Pine Creek Peatland) are located within state natural area boundaries or associated watershed protection areas. Other large peatland state natural areas (e.g. Red Lake Peatland) likely harbor large, undiscovered populations as well.
One Headwaters Chilostigman Caddisfly population is within the Finland State Forest where future development of the peatland complex or any changes that would decrease water quality or increase water temperature should be approached cautiously. At the very least, establishing buffer zones between human disturbance and C. itascae habitat would probably benefit the species. Since adult C. itascae have been collected from February through March, human activities during this time ought to be avoided.
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). Surveys by the Minnesota Biological Survey continue to seek new populations of this species as well. Vast areas of potential habitat have yet to be surveyed in northern Minnesota.
David C. Houghton, 2008 and 2017
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