Williamsonia Davis, 1913 (Corduliidae) -Boghaunters

Fig.1Fig. 2
Fig. 1:W.fletcheriexuvia from Hoodoo Lake, Wisconsin. Larva collected 10 may 1997,adult emerged 18 May 1997.
Courtesy of Wayne Steffens and Bill Smith.
Fig. 2:
W.linterni fromPoukapoag Bog, Norfolk Co., Massachusetts, USA exuvia collected by H.B. White,02 May 1970,
White and Raff1970 (UMMZODO1803, flatbed scanned by MFO)

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Page last updated: 04 June1999 (EB)

Notes onWilliamsonia in Michigan

Two species known of this genus. Severalrecords of Williamsonia fletcheri(Fig. 1) are known from the eastern UPand northern LP of Michigan. The other (type) species -W. lintneri (Fig. 2) - previously known only from the northeasternUnited States has recently been found in Mecosta Co. (S. Ross, pers.comm.), and several visual records now exist for Wisconsin. Thesesmall larvae are denizens of northeastern peatlands in sphagnum bogpools, ranging from New Brunswick west to Manitoba and south fromMaine to Michigan. Only two records are known from Michigan (seebelow, Map 1). With the discovery of several breeding sites, work isnow 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 apparentlyisolated populations inhabiting cold bogs that are difficult toaccess, it took almost 92 years before exuviae had been associatedwith the adult and generic characters were known (White and Raff1970). It also took about 70 yearsbefore larvae of W.fletcheri were associated with adults.Walker and Corbet(1975) and especially Charlton and Cannings(1993) are the best works to date ofdescribing larval characteristics as well as the biology and ecologyof Williamsonia. Larvae of Williamsonia(Fig. 1) are distinguished from allother corduliid genera by the presence of dorsal hooks on abdominalsegments 3-9 AND the absence of lateral spines on abdomimal segment8.

Only since 1970 have larvae of this genus beencollected, and known collection sites are uncommon, and what we knowabout both larval and adult biology and ecology comes from studiesconducted elsewhere in its range (Walker and Corbet1975, Charlton and Cannings1993; see also links below). No larvaehave yet been found in Michigan, but the type of habitat in whichlarvae have been found - ponds, ditches and water-filled holes ofminerotrophic bogs, sometimes in the proximity of more productivefens - abounds in the central and eastern UP as well as in thenorthern LP. With the recent location of several new sites for bothspecies in the LP, intensive efforts are being made to locateemergence sites. However, the difficulty of sampling in bog habitatsand the species' apparent early emergence (middle May to late May,perhaps early June) in the eastern part of its range is probably areason why few larval specimens have been collected, and none inMichigan. W. fletcheri is listed as Special Concern, and until actual breedingsites have been located, this designation should be retained.

Other links with information on the biology orecology of larval Williamsonia:
Briefhabitat-conservation info in Maine for W. lintmeri>>http://wlm13.umenfa.maine.edu/randy/www/tande/group/RBog.html
Moreconservation info for W.lintneri>>http://www.consci.tnc.org/library/pubs/96report/explore.html
Odonatesof Ottawa, Ontario, brief habitat notes>>http://www.ncf.carleton.ca/~bf250/odonata.html

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MichiganSpecies List

Map 1: County distribution ofW. fletcheri in Michigan.
Click on map for a larger image.

Williamsonia fletcheri Williamson,1923 - Ebony Boghaunter - Map 1
Williamsonia lintneri
(Hagen in Selys,1878) - Ringed Boghaunter - Map inpreparation

Key to the Mature Larvae of MichiganWilliamsonia

1a. Lateral spine on Ab9 about 0.38 mm, andlateral length of Ab9 approximately < 1.80 mm; length of middorsalspines 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 ofmiddorsal spines shorter than above, on Ab8 about 0.22 mm, on Ab9< 0.25 mm - W.lintneri

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Charlton,R. E. and R. A. Cannings. 1993. The larvae of Williamsonia fletcheri Williamson (Anisoptera: Corduliidae). Odonatologica22(3):335-343.

Davis, W. T. 1913.Williamsonia, a new genus of dragonflies from North America.Bulletin of the Brooklyn EntomologicalSociety 8:93-96.

Hagen, H. A., inSelys-Longshamps, M. E. de. 1878. Secondes additions au synopsis desCordulines. Bulletin del'Académie royale des Sciences de Belgique (2)45:183-222.

Walker, E. M. and J.S. Corbet. 1975. The Odonata of Canada and Alaska, Vol. 3. Universityof Toronto Press: Toronto.

White, H. B. andR. A. Raff. 1970. The nymph of Williamsonia lintneri(Hagen) (Odonata: Corduliidae). Psyche77(2):252-257.

Williamson, E. B.1923. A new species of Williamsonia (Odonata,Corduliinae). The CanadianEntomologist 55:96-98.

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