Ischnura Charpentier,1840(Coenagrionidae) - Forktails

Fig. 1:Ischnuraverticalis larva (6x, lateralview), 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.


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Page last updated: 23 July1998 (EB)

Notes on the Michigan Species of Ischnura

A genus of world-wide distribution, fourspecies have been collected in Michigan. Closely resembling larvae ofEnallagmaand Coenagrion, mature specimens can be distinguished from the formerby the distinctive banded pattern of the eyes (this can be faint orlost in preserved specimens), and (for species occuring in Michigan;however, see cautionary note in Westfall and May1996 ) by the seven, distinctlysegmented antennal segments (the last antennal segment of some matureEnallagmaindividuals may have a faint annulus).

Larvae (Figure 1) frequent wetlands, lakes andponds, and slow streams, usually with abundant aquatic vegetation.I. positatends to favor spring-fed brooks with slight current and ponds(Walker1953). I.kellicotti, known only from a couple ofsouthern Michigan counties, appears to be associated with lillypadponds (Nuphar and Nymphaea), where larvaecling to the undersides of these floating plants (Westfall and May1996). I.verticalis, by far the most common ofthe species of Ischnura in Michigan, is almost ubiquitous in any permanent ortemporary lentic environment with abundant vegetation and algae,including wetlands, ponds, lakes, and weedy, slow-moving sections ofstreams and rivers. One of the earliest odonates to emerge (perhapsour earliest damselfly in flight), adults begin to appear in earlyMay. Ponds on the UM-Dearborn campus have nearly mature larvae as ofApril 15. Populations can be multivoltine, and adults are seen onflight as late as late September. Only sphagnum bogs and muskegs tendnot to support large numbers (Walker 1953). I (EB) have collected larvae in conditions thatappear quite eutrophic and exclusive of most other odonates. Onerecord of I. perparva, a western species, was incorrectly identified and hasbeen removed from our state list (O'Brien 1997).

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

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Michigan SpeciesList

Map 1Map 2Map 3

Ischnura kellicotti Williamson,1898 - Lilypad Forktail - Map1
Ischnura posita
(Hagen, 1861) - Fragile Forktail - Map 2
Ischnura verticalis
(Say, 1839) - Eastern Forktail - Map 3

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Key toMature Larvae of Michigan Ischnura
(Adapted from Westfall and May1996)

1a. Gills without adistinct nodus, stiff setae extending almost the entire length ofboth the dorsal and ventral margins (picture); associated with lilypads - I. kellicotti

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


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

Fig. 2a1Fig. 2a2
Fig. 2a1:
Ischnuraposita exuvia (12x, lateralview), from Third Sister Lake, Washtenaw Co., Michigan, collected byJ. W. Leonard on 19 February 1932. UMMZODO-0820. Fig. 2a2: samespecimen as in Fig. 2a1 (25x, dorsal view).

2b. Gills withfewer dark crossbands (2 or 3); gills not stalked, but wideninggradually from base (Figure 2b1);; head width > 2.9mm; often with6 palpal setae (Figure 2b2); larva often strongly patterned with darkpigment - I.verticalis

Fig. 2b1 Fig. 2b2
Fig. 2b1:
Ischnuraverticalis 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 thebase can be clearly seen.

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References

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

Hagen, H. A. 1861.Synopsis of the neuroptera of North America, with a list of the SouthAmerican species. SmithsoniaMiscellaneous Collections 4:1-347.

O'Brien, M. F.Ischnura correcta. Williamsonia1(4):2.

Say, T. 1839.Descriptions of new North American neuropterous insects andobservations on some already described by (the late) Th. Say.Journal of the Academy of NaturalScience of Philadelphia 8:9-46.

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

Westfall, M.J., Jr. and M. L. May. 1996. Damselflies of North America. ScientificPublishers: 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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