Walker (1966) combined Tetragoneuria and Epicordulia as subgenera of Epitheca, though some still recognize the former two as valid genera (e.g., Garrison 1991). Epitheca (Fig. 1) is a Nearctic and Palearctic genus of 10 species, of which 4 are found in Michigan (see Maps 1-4, below).
Much of what we know about larval biology comes from Needham and Heywood (1929) and especially Kormondy (1959), the latter who wrote extensively on Tetragoneuria systematics and the subgenus' biology and ecology in Michigan. Larvae live in shallow water close to shore. Because of egg-laying habits of females, dense populations of early-instar larvae can be found, but these soon decline with inter- and intra-specific competition to a about 4 or 5 individuals per square meter. Early instars are sprawlers and active hunters, with later instar larvae becoming more sendentary, increasing the depth at which they burrow themselves in substrates. Larvae cease feeding rougly 1 (spring) or 2 to 3 (fall) weeks before emergence.
Larvae of E. canis appear limited to bog-margined lakes and ponds and their acidic discharges, and emergence usually occurs in mid to late May. These habitats are usually avoided by the other three species, which tend to prefer marshy or grassy borders of lakes and slow streams. Emergence for these three species also occurs later, from the end of May through June.
Other links with information on the biology or
ecology of larval Epitheca:
Brief habitat notes from Ottawa (Ontario, Canada) >> http://www.cyberus.ca/~jdsankey/odon2.html
1a. Distal half of dorsal surface of prementum heavily setose; palpal setae usually 4, rarely 5 (Fig. 2) - Subgenus Epicordulia, E. princeps
Fig. 2: Epitheca princeps larva (25x, dorsal view), from Radnor Lake, Davidson Co., Tennessee, collected by M. Wright on 05 May 1945. UMMZODO-1903.
1b. Distal half of dorsal surface of prementum with few very small setae; palpal setae usually 6-7, rarely 8 (Fig. 3) - Subgenus Tetragoneuria - 2
Fig. 3: Epitheca spinigera larva (25x, dorsal view), from an unknown locality in Montmorency Co., Michigan, collected by C. L. Hubbs in July, 1925. UMMZODO-0310.
2a.(1b). Lateral spine of abdominal segment. 9 short, barely attaining the level of the tips of the anal appendages (epiproct and paraprocts) (Fig. 4) - E. canis
Fig. 4: Epitheca canis larva (12x, dorsal view), from Rose Lake, Clinton Co., Michigan, collected by G. Rung on 19 April 1960. UMMZODO-2006.
2b. Lateral spine of abdominal segment 9 long, extending beyond the level of the tips of the anal appendages, usually by twice its length (Fig. 5) - 3
Fig. 5: Epitheca spinigera larva (12x, dorsal view), from an unknown locality in Montmorency Co., Michigan, collected by C. L. Hubbs in July, 1925. UMMZODO-0310.
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Caution - this couplet may not always be reliable, and, particularly for less-mature larvae, distinguishing species may not be possible.
3a.(2b). Premental setae usually not more than 10, palpal setae usually 6 (Fig. 6) - E. cynosura
Fig. 6: Epitheca cynosura larva (25x, dorsal view), from Hess Pond, Franklin Co., Columbus, Ohio, collected by M. Wright on 26 May 1939. UMMZODO-2005.
3b. Premental setae usually not less than 11, palpal setae usually 7-8 (Fig. 7) - E. spinigera
Fig. 5: Epitheca spinigera larva (25x, dorsal view), from an unknown locality in Montmorency Co., Michigan, collected by C. L. Hubbs in July, 1925. UMMZODO-0310.
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Burmeister, H. 1839. Handbuch der Entomologie. Vol 2. Enslin: Berlin, pp 397-1050.
Garrison, R. W. 1991. A synonymic list of the New World Odonata. Argia 3(2):1-30.
Hagen, H. A. 1861. Synopsis of the Neuroptera of North America, with a list of the South American species. Smithsonian Miscellaneous Collections 4:1-347.
Kormondy, E. J. 1959. The systematics of Tetragoneuria, based on ecological, life history, and morphological evidence (Odonata: Corduliidae). Miscellaneous Publications, Museum of Zoology, University of Michigan 107:1-79.
McLachlan, R. 1886. Two new species of Cordulina. Entomologists' Monthly Magazine 23:104-105.
Needham, J. G. and H. B. Heywood. 1929. A Handbook of the Dragonflies of North America (Anisoptera). C. C. Thomas: Springfield, Illinois. 378 pp.
Say, T. 1839. Descriptions of new North American neuropterous insects and observations on some already described by (the late) Th. Say. Journal of the Academy of Natural Science of Philadelphia 8:9-46.
Selys-Longchamps, M. E. de. 1871. Synopsis des Cordulines. Bulletin de l'Académie royale des Sciences de Belgique (2)31:238-316.
Walker, E. M. 1966. On the generic status of Tetragoneuria and Epicordulia (Odonata: Corduliidae). Canadian Entomologist 98:897-902.
Walker, E. M., and J. S. Corbet. 1975. The Odonata of Canada and Alaska, Vol. 3. University of Toronto Press: Toronto, Ontario. xvi + 308.