Dromogomphus Selys 1854 - Spinylegs


Fig. 1: Dromogomphus spinosus, exuvia, from Ives Lake, Marquette Co., Michigan,
collected by M. F. O'Brien on 02 July 1996. UMMZODO-1247

Notes - Michigan Species List - References
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Page last updated: 17 July 1998 (EB)

Notes on the Michigan larvae of Dromogomphus

Two of the three species of this eastern North American genus have been recorded in Michigan. Dromogomphus spoliatus is now known from Wayne County, along the Huron River (Craves and O'Brien, 2002).


Map 1: County distribution of Dromogomphus spinosus in Michigan
Click on map for a larger image

Westfall and Tennessen (1979) expand on Wright's (1946) older work to provide the most recent taxonomic treatment for the genus. These are large (last instars usually measure about 32-35 mm), elongate gomphid larvae, distinctive for their large, dark mid-dorsal abdominal spines, and this character will help distinguish this species from larvae of Gomphus graslinellus and G. lividus to which there is some resemblance. The dark mid-dorsal abdominal ridge and spines usually are clearly distinguished from the lighter ground color of the abdominal segment, and this color in larvae and exuviae often remains after long-term preservation in alcohol (pers. obs.).

Larvae can be fairly common in rocky lake margins as well as large rivers and stream rapids. Walker (1958) remarks that this species is the most common late summer gomphid of large streams and lakes in southern Ontario. Larvae apparently crawl several feet from the water's edge upon a log or rock to emerge. Very little is known about the ecology or biology of this genus. In Michigan, adults appear to emerge from mid-June through July, based on observations from F. Locke (July 1940, Washtenaw Co.), E. J. Kormondy (25 June 1953, Douglas Lake, Cheboygan Co.), T. Nowicki (28 June 1997, Green Lake, Benzie Co.) and E. Bright (27 June 1996, Ives Lake, Marquette Co.).

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Michigan Species List

Dromogomphus spinosus Selys, 1854 - Black-shouldered Spinyleg
*Dromogomphus spoliatus (Hagen in Selys, 1858) - Flag-tailed Spinyleg

*Not recorded in Michigan, but may be encountered in the southern LP

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Key to the Mature Larvae of Dromogomphus
(References:
Wright 1946 and Westfall and Tennessen 1979)

1a. Mid-dorsal processes on abdominal segments 5- or 6-9 (Fig. 2); lateral spines on abdominal segment 9 about 1.5x the length of those on segment 8 (Fig. 3); small, stout spines along lateral margins of abdominal segments 7, 8 and 9 (Fig. 4); end tooth of palpal lobe 2.0x as long as smaller teeth next to it (Fig. 5) - D. spinosus

Fig. 2 Fig. 3 Fig. 4 Fig. 5
Fig. 2: (6x, dorsal view),
Dromogomphus spinosus larva, from Third Sister Lake, Washtenaw Co., Michigan, collected by F. Locke in July 1940. UMMZODO-0562. Fig. 3: (12.5x, dorsal view): Dromogomphus spinosus exuvia, from Ives Lake, Marquette Co., Michigan, collected by M. F. O'Brien on 02 July 1996. UMMZODO-1247; Fig. 4: (12.5x, dorsal view), Dromogomphus spinosus larva, from Third Sister Lake, Washtenaw Co., Michigan, collected by F. Locke in July 1940. UMMZODO-0562.; Fig. 5: (25x, ventral view), Dromogomphus spinosus larva, from Third Sister Lake, Washtenaw Co., Michigan, collected by F. Locke in July 1940. UMMZODO-0562.

1b. Mid-dorsal processes on abdominal segments 8 and 9, absent on segments 5, 6 and 7 (Fig. 6); lateral spines on abdominal segment 9 about 3.0x as long as those on segment 8 (Fig. 7); small, stout spines along lateral margins of abdominal segment 9, sometimes along segment 8, but absent along segment 7 (Fig. 8); end tooth of palpal lobe less than 2.0x as long as smaller teeth next to it (Fig. 9) - D. spoliatus

Fig. 6 Fig. 7 Fig. 8 Fig. 9
Figs. 6 (6x, dorsal view), 7 (12.5x, dorsal view), 8 (12.5x, dorsal view) and 9 (25x, ventral view):
Dromogomphus spoliatus exuvia, from Fort Wayne, Allen Co., Indiana, collected by E. B. Williamson on 03 August 1902. UMMZODO-1597.

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References

Craves, J.A and D.S. O'Brien. 2002. Dromogomphus spoliatus (Odonata: Gomphidae) new for Michigan. Great Lakes Entomologist 35(2):115-116.

Selys-Longchamps, M. E. de. 1854. Synopsis des Gomphines. Bulletin de l'Académie royale des Sciences de Belgique 21:23-114.

Selys-Longchamps, M. E. de. 1858. Monographie des Gomphines. Mémoires de la Société Royale des Sciences de Liége 9:1-460, 23 pls. (Note: some authors reference this work as being published in 1857. The copy here in the E. B.Williamson Library, UMMZ, has a published date in the frontpiece as "Novembre 1857," but the supplemental plates at the end of the work, by H. A. Hagen, are clearly dated 1858).

Walker, E. M. 1958. The Odonata of Canada and Alaska, Vol. 2. University of Toronto Press: Toronto. xii + 318.

Westfall, M. J., Jr. and K. J. Tennessen. 1979. Taxonomic clarification within the genus Dromogomphus Selys (Odonata: Gomphidae). The Florida Entomologist 62(3):266-273.

Wright, M. 1946. Taxonomic notes on the nymphs of the dragonfly genus Dromogomphus Selys. Journal of the Tennessee Academy of Science 21:183-186.

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revised, July, 2010.