Two species known of this genus. Several records of Williamsonia fletcheri (Fig. 1) are known from the eastern UP and northern LP of Michigan. The other (type) species - W. lintneri (Fig. 2) - previously known only from the northeastern United States has been found in several counties in the UP and LP. These small larvae are denizens of northeastern peatlands in sphagnum bog pools, ranging from New Brunswick west to Manitoba and south from Maine to Michigan. With the discovery of several breeding sites, work is now being done to describe exact habitat conditions.
Davis (1913) erected Williamsonia for a species (lintneri) described by Hagen in 1878. With an early emergence and apparently isolated populations inhabiting cold bogs that are difficult to access, it took almost 92 years before exuviae had been associated with the adult and generic characters were known (White and Raff 1970). It also took about 70 years before larvae of W. fletcheri were associated with adults. Walker and Corbet (1975) and especially Charlton and Cannings (1993) are the best works to date of describing larval characteristics as well as the biology and ecology of Williamsonia. Larvae of Williamsonia (Fig. 1) are distinguished from all other corduliid genera by the presence of dorsal hooks on abdominal segments 3-9 AND the absence of lateral spines on abdomimal segment 8.
Only since 1970 have larvae of this genus been collected, and known collection sites are uncommon, and what we know about both larval and adult biology and ecology comes from studies conducted elsewhere in its range (Walker and Corbet 1975, Charlton and Cannings 1993; see also links below). No larvae have yet been found in Michigan, but the type of habitat in which larvae have been found - ponds, ditches and water-filled holes of minerotrophic bogs, sometimes in the proximity of more productive fens - abounds in the central and eastern UP as well as in the northern LP. With the recent location of several new sites for both species in the LP, intensive efforts are being made to locate emergence sites. However, the difficulty of sampling in bog habitats and the species' apparent early emergence (middle May to late May, perhaps early June) in the eastern part of its range is probably a reason why few larval specimens have been collected, and none in Michigan. W. fletcheri is listed as Special Concern, and until actual breeding sites have been located, this designation should be retained.
Other links with information on the biology or
ecology of larval Williamsonia:
Brief habitat-conservation info in Maine for W. lintmeri >>http://wlm13.umenfa.maine.edu/randy/www/tande/group/RBog.html
More conservation info for W. lintneri >>http://www.consci.tnc.org/library/pubs/96report/explore.html
Odonates of Ottawa, Ontario, brief habitat notes >>http://www.ncf.carleton.ca/~bf250/odonata.html
1a. Lateral spine on Ab9 about 0.38 mm, and lateral length of Ab9 approximately < 1.80 mm; length of middorsal spines on Ab8 about 0.34 mm, on Ab9 about 0.35 mm - W. fletcheri
1b. Lateral spine on Ab9 longer than above, about 0.55 mm, and lateral length of Ab9 > 2.00 mm; length of middorsal spines shorter than above, on Ab8 about 0.22 mm, on Ab9 < 0.25 mm - W. lintneri
Charlton, R. E. and R. A. Cannings. 1993. The larvae of Williamsonia fletcheri Williamson (Anisoptera: Corduliidae). Odonatologica 22(3):335-343.
Davis, W. T. 1913. Williamsonia, a new genus of dragonflies from North America. Bulletin of the Brooklyn Entomological Society 8:93-96.
DuBois, R.B., J.M. Pleski, W.A. Smith, & E.J. Epstein. 2009. Odonata of coastal peatland habitats adjacent to Lake Superior in Wisconsin. The Great Lakes Entomologist 42(3&4):158-172.
Hagen, H. A., in Selys-Longshamps, M. E. de. 1878. Secondes additions au synopsis des Cordulines. Bulletin de l'Académie royale des Sciences de Belgique (2)45:183-222.
O'Brien, M.F. 2006. Additional localities for Williamsonia lintneri in Michigan. Williamsonia. 10(1):3.
Ross, S. and M.O'Brien. 1999. Williamsonia lintneri (Odonata: Corduliidae). A first Michigan record with additional notes on W. fletcheri. The Great Lakes Entomologist 32:201-205.
Walker, E. M. and J. S. Corbet. 1975. The Odonata of Canada and Alaska, Vol. 3. University of Toronto Press: Toronto.
White, H. B. and R. A. Raff. 1970. The nymph of Williamsonia lintneri (Hagen) (Odonata: Corduliidae). Psyche 77(2):252-257.
Williamson, E. B. 1923. A new species of Williamsonia (Odonata, Corduliinae). The Canadian Entomologist 55:96-98.