Caddisflies: a Farulan caddisfly
(Trichoptera: Uenoidae: Uenoinae) Profile prepared by Sarah Foltz, The Xerces Society for Invertebrate Conservation
Farula constricta is a rather recently described species, known from four to five small streams in the Columbia River Gorge, Oregon. Due to its extreme rarity and restricted habitat, this species is critically imperiled and vulnerable to extinction. The scenic and heavily trafficked Historic Columbia River Highway crosses most, if not all, of the streams occupied by this species, and sedimentation, eutrophication, and chemical pollution caused by road construction and impervious surface run-off could impact this species. Water-temperature changes caused by timber harvest and continued global climate change may also threaten this species, in addition to sedimentation and bank erosion by heavy recreational activity. Undisturbed buffers of coniferous forest around stream habitat may be critical for the survival of this species.
Adult: a small, moth-like insect, uniform dark brown in color, with a forewing length of 5 mm (0.2 in.) in both sexes (Wiggins and Wisseman 1992). Adults are typical for the genus in general structure, and have the curved and heavily setate internal branches of segment X, and the swollen mesal lobe of the inferior appendages also seen in the closely related F. rainieri. Farula constricta is distinguished by a sharp restriction in the mesal lobes of the inferior appendages, and by a constriction at the base of the internal branch of X, both in ventral aspect. The male genitalia are characterized as follows: segment IX recessed into VIII, dorsum incomplete, semi-membranous posterolaterally; divided dorsum of IX covered by thin irregular membrane which also overlies bases of internal branches of X; inferior appendages as in F. rainieri, base of mesal lobe broad but abruptly constricted to slender pointed apex in ventral aspect; lateral lobe of inferior appendages with setae denser and longer towards clavate apex. Segment X with internal branch much shorter than external branch, constricted basally in lateral aspect, greatly enlarged toward apex, sharply angulate in dorsal aspect, mesal surface bearing many stout setae toward apex; external branch of X about one and one-half times longer than internal branch, slender, with sharp apical point directed mesad; inferior branch of segment X heavily sclerotized, terminating in pair of blunt hooked processes, and with a broad point at each side near base; prenal appendages setate, rather small. Phallus typical for Farula, spoon-shaped dorsally with slender sclerotized tube at the apex. The female genitalia are typical for the genus and not distinguished from other species (Wiggins and Wisseman 1992).
Immature: Although the larvae of this species are known, a complete description is not available at this time (Wisseman 2008, pers. comm.). Larvae of the genus Farula make extremely slender portable cases, lack abdominal gills, and their sclerotized parts are mostly uniform dark brown or black (Wiggins 1996). The smoothly textured cases, so slender they could be mistaken for pine-needles (Wiggins 1996), are constructed of small sand grains fitted closely together and covered externally and internally with a thin silken lining (Wiggins 1996, Merritt et al. 2008). Cases can be up to 14.5 mm (0.6 in.) in length. Farula is further distinguished from other genera in the Uenoidae family by the following characters: pronotum broadest anteriorly in dorsal aspect, mesonotal sclerites with anterior margin rounded and single median notch between two sclerites, pronotum with anterior margin and anterolateral corner curved, darkened posterolateral corner of each mesonotal sclerite not reaching the mid-lateral point of sclerite, abdomen with filaments of lateral fringe scattered and arising over less than half of most segments, but with prominent and discrete tuft of filaments at the anterior edge of segment II (Wiggins 1996).
Pupa: In this genus, larval cases are converted into pupal chambers by a silken sieve membrane spun across the inside posterior opening of the case (Wiggins 1996).
This rather recently described species has been collected from four to five small streams in the Columbia River Gorge (Hood River County: Eagle Creek (2003); Multnomah County: Mist Falls near Wahkeena Creek (1989); Oneonta Creek in Oneonta Gorge (2003); a small unnamed stream 0.9 miles west of Oneonta Creek (1989); and a stream between Multnomah Falls and Oneonta Falls (2003, possibly the same stream as the 1989 record)). Although it is possible that the species is extremely isolated in its distribution and confined to a few short reaches of the above streams (Wisseman 2006, pers. comm.), further surveys in small, nearby streams may reveal additional populations.
Forest Service/BLM lands: Documented occurrences are in the Columbia River Gorge National Scenic Area/Mount Hood National Forest.
Most trichopteran species have highly specific preferences with regard to water temperature, velocity, dissolved-oxygen levels, and substrate characteristics, and are therefore sensitive to a wide array of habitat alterations. Sedimentation, eutrophication, and chemical pollution caused by road construction and impervious surface run-off could impact this species. The scenic and heavily trafficked Historic Columbia River Highway crosses most, if not all, of the streams occupied by this species, and current road construction at the Oneonta Creek bridge may impact the Oneonta population of this species. Ongoing work at this site involves construction of a paved parking area east of the Oneonta Tunnel, and reconstruction of the tunnel (Friends of the Historic Columbia River Highway, 2008).
Both Oneonta Gorge and Eagle Creek are among the most popular hiking and camping destinations in the Columbia River Gorge (USFS 2007), and recreational use at these sites is expected to intensify in the future, due to both local population growth and national recreation trends (Cordell et al., 1996). Sedimentation and bank erosion by heavy recreational activity, as well as recent landslides (Salem-News 2008), could impact this species.
The loss of trees through timber harvest poses additional threats, since this species occupies forested habitats, and trees provide shade that maintains appropriate water levels and temperatures for larval and pupal development. Continued global climate change raises further issues for this cold-water species: projected changes from this phenomenon include increased frequency and severity of seasonal droughts and flooding, reduced snowpack to feed river flow, increased siltation, and increased air and water temperatures (Field et al. 2007), all of which could unfavorably impact this species’ habitat and long-term survival.
Inventory: Further surveys at and around the known sites are needed to help establish the current status of this species. Similar cold-water streams in the region (Mt. Hood National Forest and Columbia River Gorge) should also be explored for suitable habitat, and surveyed for this species. Since population size is important in evaluating the stability of a species at a given locality, abundance estimates of this species would also be valuable.
Management: Protect all new sites and their associated watersheds from heavy recreational use, timber harvest, and other practices that would adversely affect aspects of this species’ life cycle. Undisturbed buffers of coniferous forest around stream habitat may be critical for the survival of species within the Farula genus (Applegarth 1995). Riparian habitat protection, including maintenance of water quality, substrate conditions, and canopy cover, would likely benefit and help maintain this species.
Applegarth, J.S. 1995. Invertebrates of special status or special concern in the Eugene district. U.S. Department of the Interior, Bureau of Land Management. Eugene, OR. 126 pp.
Cordell, H.K., McDonald, B.L., Teasley, R.J., Bergstrom, J.C., Martin, J., Bason, J., and Leeworthy, V.R. 1996. Outdoor recreation participation trends. In: Outdoor recreation in American life: a national assessment of demand and supply trends (Cordell, H.K., Betz, C.J., Bowker, C.J., eds.). Sagamore Publishing, Champaign, IL. 449 pp. Available at: http://www.srs.fs.usda.gov/pubs/ja/ja_cordell010.pdf.
Field, C.B., Mortsch, L.D., Brklacich, M., Forbes, D.L., Kovacs, P., Patz, J.A., Running, S.W. and M.J. Scott. 2007. Chapter 14: North America. In: Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Parry, M.L., Canziani, O.F., Palutikof, J.P., van der Linden, P.J. and Hanson, C.E., eds.). Cambridge University Press, Cambridge, UK. Available at: www.ipcc.ch/pdf/assessment-report/ar4/wg2/ar4-wg2-chapter14.pdf.
Friends of the Historic Columbia River Highway, 2008. Road Construction and Closures: Oneonta Gorge Parking and Vista. 9 Dec. 2008. .
Merritt, R.W., Cummins, K.W., and M.B. Berg. 2008. An introduction to the aquatic insects of North America. Fourth Edition. Kendall/Hunt Publishing Co., Dubuque, Iowa. 1158pp.
NatureServe. 2008. “Farula constricta.” NatureServe Explorer: An online encyclopedia of life [web application]. Feb. 2008. Version 7.0. NatureServe, Arlington, Virginia. 21 Oct. 2008. .
Salem-News. October 12th 2008. “Man dies and family of five injured in incidents near Multnomah Falls.” 26 Dec. 2008. .
United States Forest Service. 2007. Columbia River Gorge National Scenic Area: Trails. 9 Dec. 2008 .
Wiggens, G.B. 1996. Larvae of the North American Caddisfly Genera (Trichoptera). Second Edition. Toronto and Buffalo: University of Toronto Press, 457pp.
Wiggins, G.B. and Wisseman, R.W. 1992. New North American species in the genera Neothremma and Farula, with hypotheses on phylogeny and biogeography (Trichoptera: Uenoidae). Can. Ent. 124: 1063-1074.
Wisseman, R.W. 2006. Personal communication with Eric Scheuering.
Wisseman, R.W. 2008. Personal communication with Sarah Foltz.