Ischnura Charpentier, 1840 (Coenagrionidae) - Forktails

Fig. 1: Ischnura verticalis larva (6x, lateral view), from lake in Hillsdale State Game Area, Hillsdale Co.,
UMMZODO-1179.


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Notes on the Michigan Species of Ischnura

A genus of world-wide distribution, four species have been collected in Michigan. Closely resembling larvae of Enallagma and Coenagrion, mature specimens can be distinguished from the former by the distinctive banded pattern of the eyes (this can be faint or lost in preserved specimens), and (for species occuring in Michigan; however, see cautionary note in Westfall and May 1996 ) by the seven, distinctly segmented antennal segments (the last antennal segment of some mature Enallagma individuals may have a faint annulus).

Larvae (Figure 1) frequent wetlands, lakes and ponds, and slow streams, usually with abundant aquatic vegetation. I. posita tends to favor spring-fed brooks with slight current and ponds (Walker 1953). I. kellicotti, known only from a couple of southern Michigan counties, appears to be associated with lillypad ponds (Nuphar and Nymphaea), where larvae cling to the undersides of these floating plants (Westfall and May 1996). I. verticalis, by far the most common of the species of Ischnura in Michigan, is almost ubiquitous in any permanent or temporary lentic environment with abundant vegetation and algae, including wetlands, ponds, lakes, and weedy, slow-moving sections of streams and rivers. One of the earliest odonates to emerge (perhaps our earliest damselfly in flight), adults begin to appear in early May. Ponds on the UM-Dearborn campus have nearly mature larvae as of April 15. Populations can be multivoltine, and adults are seen on flight as late as late September. Only sphagnum bogs and muskegs tend not to support large numbers (Walker 1953). I (EB) have collected larvae in conditions that appear quite eutrophic and exclusive of most other odonates. One record of I. perparva, a western species, was incorrectly identified and has been removed from our state list (O'Brien 1997).

Other links with information on the biology or ecology of larval Ischnura:
none found as of 15 February 1998

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Michigan Species List

Map 1 Map 2 Map 3

Ischnura kellicotti Williamson, 1898 - Lilypad Forktail - Map 1
Ischnura posita
(Hagen, 1861) - Fragile Forktail - Map 2
Ischnura verticalis
(Say, 1839) - Eastern Forktail - Map 3

Ischnura hastata (Say) -Citrine Forktail - Map 4

 

 

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Key to Mature Larvae of Michigan Ischnura
(Adapted from Westfall and May 1996)

1a. Gills without a distinct nodus, stiff setae extending almost the entire length of both the dorsal and ventral margins (picture); associated with lily pads - I. kellicotti

1b. Gills with a more or less distinct nodus, stiff setae extending not more than about 2/3 of their length (picture) - 2


2a.(1b). Gills usually with 3 to 8 dark crossbands at and beyond the nodus, sometimes faint and hard to see, especially distally; gills often somewhat stalked, the part proximal to the nodus somewhat narrowed (Figure 2a1); head width < 2.9 mm; palpal setae almost always 5 (Figure 2a2) - I. posita

Fig. 2a1 Fig. 2a2
Fig. 2a1:
Ischnura posita exuvia (12x, lateral view), from Third Sister Lake, Washtenaw Co., Michigan, collected by J. W. Leonard on 19 February 1932. UMMZODO-0820. Fig. 2a2: same specimen as in Fig. 2a1 (25x, dorsal view).

2b. Gills with fewer dark crossbands (2 or 3); gills not stalked, but widening gradually from base (Figure 2b1);; head width > 2.9mm; often with 6 palpal setae (Figure 2b2); larva often strongly patterned with dark pigment - I. verticalis

Fig. 2b1 Fig. 2b2
Fig. 2b1:
Ischnura verticalis larva (12x, lateral view), from lake in Hillsdale State Game Area, Hillsdale Co., Michigan, collected by M. F. O'Brien and E. Bright on 02 May 1997. UMMZODO-1179. Fig. 2b2: Same specimen as in Fig. 2b1 (25x, dorsal-lateral view). Note: Setae No. 1 is partially broken, but the base can be clearly seen.

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References

Charpentier, T. de. 1840. Libellulinae europaeae descriptae e depictae. Lipsiae, Leopold Voss. 180 pp.

Craves, J. A. and D. S. O’Brien. 2002. Ischnura hastata (Odonata: Coenagrionidae): New for Michigan. The Great Lakes Entomologist 35:21-23.

Hagen, H. A. 1861. Synopsis of the neuroptera of North America, with a list of the South American species. Smithsonia Miscellaneous Collections 4:1-347.

O'Brien, M. F. Ischnura correcta. Williamsonia 1(4):2.

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.

Walker, E. M. 1953. The Odonata of Canada and Alaska, Vol. 1. University of Toronto Press: Toronto, Ontario. xi + 292 pp.

Westfall, M. J., Jr. and M. L. May. 1996. Damselflies of North America. Scientific Publishers: Gainesville, Florida. x + 650 pp.

Williamson, E. B. 1898. A new species of Ischnura (Order Odonata).Entomological News 9(9):209-211, pl. 9.

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