Ischnura gemina - (Kennedy, 1917)
San Francisco Forktail
Other English Common Names: San Francisco forktail
Synonym(s): Celaenura gemina
Taxonomic Status: Accepted
Related ITIS Name(s): Ischnura gemina (Kennedy, 1917) (TSN 592508)
Unique Identifier: ELEMENT_GLOBAL.2.109487
Element Code: IIODO72010
Informal Taxonomy: Animals, Invertebrates - Insects - Dragonflies and Damselflies
Kingdom Phylum Class Order Family Genus
Animalia Mandibulata Insecta Odonata Coenagrionidae Ischnura
Genus Size: D - Medium to large genus (21+ species)
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Concept Reference
Concept Reference: Paulson, D.R. and S.W. Dunkle. 1999. A Checklist of North American Odonata. Slater Museum of Natural History, University of Puget Sound Occasional Paper, 56: 86 pp. Available:
Concept Reference Code: A99PAU01EHUS
Name Used in Concept Reference: Ischnura gemina
Taxonomic Comments: Known to hybridize with I. denticolla (Leong and Hafernik, 1992). In subgenus Celaenura (Novak and Robinson, 1996).
Conservation Status

NatureServe Status

Global Status: G2
Global Status Last Reviewed: 02Dec2008
Global Status Last Changed: 02Aug1998
Rounded Global Status: G2 - Imperiled
Reasons: This species is endemic to the San Francisco Bay Area. Several small populations have gone extinct since their discovery, however there are indications of range expansion. More survey data are needed.
Nation: United States
National Status: N2 (02Aug1998)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States California (S2)

Other Statuses

IUCN Red List Category: VU - Vulnerable

NatureServe Global Conservation Status Factors

Range Extent: 250-20,000 square km (about 100-8000 square miles)
Range Extent Comments: Endemic to a tiny range in the Greater San Francisco area of California only, probably <500 square miles. However, recent photographs and sightings (Biggs, pers. comm. in Bick, 2003) indicate that the species may extend north-south slightly beyond the Bay Area.

Number of Occurrences: 6 - 20
Number of Occurrences Comments: There are more than 10 known locations (Abbott, 2007).

Population Size: 1000 - 2500 individuals
Population Size Comments: Probably no more than a few hundred at each site, perhaps 500-1,000 at best sites (Garrison and Hafernik 1981).

Overall Threat Impact Comments: Historically some populations have been extirpated due to urbanization and some habitat has naturally converted from small shallow ponds to dry pond beds; this succession is still a threat. Draining of wetlands for housing and industry, as well as channeling creeks for flood control, has greatly reduced and altered wetlands in the Bay Area (Hafernik, 1992 in Connor et al., 2002). Hybridizes with Ischnura denticollis (Leong and Hafernik, 1992) which is a may threaten its existence (Bick, 2003; Dunkle, 2004).

Short-term Trend: Decline of 10-30%
Short-term Trend Comments: Several small populations have gone extinct since their discovery.

Intrinsic Vulnerability Comments: Relatively long life and good dispersal ability provides opportunity to take advantage of newly formed habitats; apparently tolerates some disturbance/pollution.

Other NatureServe Conservation Status Information

Inventory Needs: Intense search of range for occurrences, especially in natural and (very important) protected sites.

Global Range: (250-20,000 square km (about 100-8000 square miles)) Endemic to a tiny range in the Greater San Francisco area of California only, probably <500 square miles. However, recent photographs and sightings (Biggs, pers. comm. in Bick, 2003) indicate that the species may extend north-south slightly beyond the Bay Area.

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: endemic to a single state or province

U.S. & Canada State/Province Distribution
United States CA

Range Map
No map available.

U.S. Distribution by County Help
State County Name (FIPS Code)
CA Marin (06041), San Francisco (06075)*, San Mateo (06081)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
18 San Francisco Bay (18050004)+, Tomales-Drake Bays (18050005)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
Basic Description: Very small blue-tipped forktail damselfly.
General Description: Male a small mostly black damselfly with blue sides on the thorax, and blue dorsal spots on abdominal segments 9 and 10. Females usually dull green on sides of thorax. (Kennedy, 1917)
Diagnostic Characteristics: Very similar to I. DENTICOLLIS, but male cerci in dorsal view are pointed and divergent, those of DENTICOLLIS look square. Female DENTICOLLIS have a pair of tubercles on the prothorax, these are lacking in gemina. Male larvae have globular cerci. (Garrison, 1981)
Ecology Comments: Habitat is marshy seepage areas, ponds, and canals.
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Mobility and Migration Comments: Able to colonize newly created habitats.
Lacustrine Habitat(s): Shallow water
Palustrine Habitat(s): HERBACEOUS WETLAND
Habitat Comments: Found in small, mostly open seepages, ponds, and canals, covered with floating vegetation. Eggs are laid in aquatic plants, larvae cling to submerged plants, adults forage among herbs and shrubs. Apparently is somewhat adaptable, but prefers sluggish shallow water without many fish.
Adult Food Habits: Invertivore
Immature Food Habits: Invertivore
Adult Phenology: Diurnal
Phenology Comments: Larvae overwinter, flight season early March to mid November.
Length: 2.5 centimeters
Economic Attributes Not yet assessed
Management Summary
Biological Research Needs: (1) Details of larval ecology; (2) resistance to urban pollution; (3) likelihood of captive rearing.
Population/Occurrence Delineation
Group Name: Pond-Breeding Odonates

Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on some evidence of historical or current presence of single or multiple specimens ideally with evidence of on-site breeding (teneral adults, mating pairs, territorial males, ovipositing females, larvae, or exuviae) at a given location with potential breeding habitat. Although oviposition may not necessarily yield progeny that survive to adulthood (Fincke, 1992) and movements resembling oviposition may not necessarily result in egg deposition (Okazawa and Ubukata, 1978; Martens, 1992; 1994), presence of on-site oviposition is here accepted as an indicator of a minimum element occurrence because the time and effort involved in determining success of emergence is beyond the scope of the general survey. As adults of some species might disperse moderate distances (see below), only sites with available larval habitat can be considered appropriate for a minimum occurrence. Single, non-breeding adults captured away from potential suitable breeding habitat should not be treated as element occurrences. Evidence is derived from reliable published observation or collection data; unpublished, though documented (i.e. government or agency reports, web sites, etc.) observation or collection data; or museum specimen information. A photograph may be accepted as documentation of an element occurrence for adults only (nymphs and subimagos are too difficult to identify in this manner) provided that the photograph shows diagnostic features that clearly delineate the species from other species with similar features. Sight records, though valuable, should not be accepted as the basis for new element occurrences. Instead, such records should be utilized to further study an area to verify the element occurrence in that area.
Separation Barriers: Within catchments there are likely no significant barriers to movement of sexually mature adults between microhabitats, with even extensive sections of inappropriate waterway or major obstructions to flow being readily traversed by adults within the flight season.
Separation Distance for Unsuitable Habitat: 3 km
Separation Distance for Suitable Habitat: 3 km
Separation Justification: Adults odonates are known to wander, some over great distances (not so for damselflies). Mass migration over great distances is not herein considered when drafting separation distances as such behavior is limited to few species (e.g. Anax junius, Libellula quadrimaculata, other Libellula spp., Sympetrum spp.), occurs unpredictably and infrequently (10 year cycles for L. quadrimaculata), are unidirectional or intergenerational (Freeland et al., 2003), or occurs under unusual circumstances such as irritation by trematode parasites (Dumont and Hinnekint, 1973) or major weather events (Moskowitz et al., 2001; Russell et al., 1998).

Corbet (1999) estimated average distance traveled for a commuting flight (between reproductive and foraging sites) to be less than 200 m but sometimes greater than one km. Pond-breeding odonates may wander but generally stay within a few km of their emergence pond. At the species level, overall range (and dispsersal capability) tends to be larger than for lotic species possibly in response to greater instability of lentic versus lotic habitat over time (Hof et al., 2006). Distribution is often limited in response to presence or absence of predators (also dependent on habitat permanence) (McPeek, 1989; Stoks and McPeek, 2003a; 2003b). At night and during inclement weather, adult Procordulia grayi roosted at least one km away from the reproductive site (Rowe, 1987). Conrad et al. (1999) listed maximum dispersal distance of Sympetrum sanguieneum at 1.2 km but at 800 m or less with high dispersal rate between ponds for other species (Ischnura elegans, Coenagrion puella, C. pulchellum, Lestes sponsa, Enallagma cyathigerum, and Pyrrhosoma nymphalis). Michiels and Dhondt (1991) cited dispersal distance of Sympetrum donae in Belgium at greater than 1.75 km and most mature adults immigrated away from the emergence site. Moore (1986) cited several species of Enallagma as dispersing 2.7 km and found no colonization of artificial acid water ponds in eastern England constructed at least 5 km from colonized natural ponds in 12 consecutive years (single introduced population of Ceriagrion tenellum not surviving past the second generation). Purse et al. (2003) found mature adults of the rare European damselfly, Coenagrion mercuriale, had a low rate of movement within continuous habitat (< 25 m), low emigration rates (1.3 to 11.4%), and low colonization distances (max. 1 km), comparable to other similarly sized coenagrionids.

Even within genera, however, differences in dispersal patterns may exist. McPeek (1989) found the mechanisms causing Enallagma movements between Michigan lakes were due to propensity to leave natal lakes, not active selection of different habitats (e.g. lakes with fish, without fish, or winterkill lakes with fish part-year). With the exception of winterkill lake species (Enallagma ebrium), species in lakes with fish (E. geminatum, E. hageni) and fishless lake species (E. boreale, E. cyathigerum), moved little or not at all away from natal lakes; even those less than 10 m apart. Natural selection may favor remaining at natal lakes where ecological conditions are constant and dispersal costs (i.e. mortality) high (McPeek, 1989). Uncharacteristic movement of E. ebrium away from natal lakes is explained by recolonization of lakes in which populations have been reduced or eliminated and reproducing when winterkill of fish populations changes a lake to the fishless condition.

Considering the above tendency for pond breeding odonates to remain at or near (order of hundreds of meters) natal emergence sites, separation distance has been set at 3 km.

Inferred Minimum Extent of Habitat Use (when actual extent is unknown): .5 km
Inferred Minimum Extent Justification: The few studies determining area of adult foraging habitat surrounding breeding sites have indicated a range of 30 meters to 300 meters [see Briggs (1993) for Enallagma laterale; Corbet (1999) for Nesciothemis nigeriensis and Calopteryx haemorrhoidalis; Beukeman (2002) for Calopteryx haemorrhoidalis; and Samways and Steytler (1996) for Chorolestes tessalatus]. As a result, an element occurrence should include the breeding site and surrounding pond or upland habitat extending 500 m in a radius from the breeding site.
Date: 12Feb2007
Author: Cordeiro, J.
Population/Occurrence Viability
U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
NatureServe Conservation Status Factors Edition Date: 02Dec2008
NatureServe Conservation Status Factors Author: Dunkle, S.W.; Paulson, Dennis R. [1998]; Capuano, N. (2008)
Element Ecology & Life History Edition Date: 04Mar1991
Element Ecology & Life History Author(s): DUNKLE, S.W., SCHWEITZER, D.F.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

  • Abbott, J.C. 2007. Ischnura gemina. In: IUCN 2008. 2008 IUCN Red List of Threatened Species. Downloaded on 02 December 2008.

  • Bick, G.H. 1983. Odonata at risk in conterminous United States and Canada. Odonatologica 12(3):209-226.

  • Bick, G.H. 2003. At-risk odonata of conterminus United States. Bulletin of American Odonatology 7(3):41-56

  • Connor, E.F., J. Hafernik, J. Levy, V.L. Moore and J.K. Rickman. 2002. Insect conservation in an urban biodiversity hotspot: The San Francisco Bay Area. Journal of Insect Conservation 6:247-259.

  • Dunkle, S. W. 2004. Critical species of Odonata in North America. International Journal of Odonatology 7(2):149-162.

  • Garrison, R.W. 1981. Description of the larva of ISCHNURA GEMINA with a key and new characters for the separation of sympatric ISCHNURA larvae. Annals of the Ent. soc. of America, 74(6):525-530.

  • Garrison, R.W., and J.E. Hafernik. 1981a. Population structure of the rare damselfly, Ischnura gemina (Kennedy) (Odonata: Coenagrionidae). Oecologia (Berl) 48:377-384.

  • Garrison, R.W., and J.E. Hafernik. 1981b. The distribution of Ischnura gemina (Kennedy) and a description of the andromorph female (Zygoptera:Coenagrionidae). Odonatologica 10(2):85-91.

  • Hafernik, J.E., and R.W. Garrison. 1986. Mating success and survival rate in a population of damselflies: results at variance with theory? American Naturalists 128(3):353-365.

  • Hannon E.R., and J.E. Hafernik. 2007. Reintroduction of the rare damselfly Ischnura gemina (Odonata: Coenagrionidae) into an urban California park. Journal of Insect Conservation 11(2):141-149.

  • Kennedy, C.H. 1915. Notes on the Life History and Ecology of the Dragonflies (Odonata) of Central California and Nevada. Proc. U.S. Nat. Mus., vol. 52, no. 2192. pp. 483-635.

  • Leong, J.M., and J.E. Hafernik, Jr. 1992. Hybridization between two damselfly species: Morphometric and genitalis differentiation. Annals of the Entomological Society of America 85(6):662-670.

  • Novak, K.L. and J.V. Robinson. 1996. A unique morphology, common to the penes of the CELAENURA and NANOSURA groups of ISCHNURA (Zygoptera: Coenagrionidae). Odonatologica 25(2):183-186.

  • Paulson, D.R. and S.W. Dunkle. 1999. A Checklist of North American Odonata. Slater Museum of Natural History, University of Puget Sound Occasional Paper, 56: 86 pp. Available:

  • Paulson, D.R., and S.W. Dunkle. 2009. A checklist of North American Odonata including English name, etymology, type locality, and distribution. Originally published as Occasional Paper No. 56, Slater Museum of Natural History, University of Puget Sound, June 1999; completely revised March 2009. Online. Available:

  • Perkins, P. D. 1983. North American insect status review. Contract 14-16-0009-79-052. Final report to Office of Endangered Species, U.S. Fish and Wildlife Service, Department of the Interior. 354 pp.

  • Saux, C., C. Simon, and G.S. Spicer. 2003. Phylogeny of the dragonfly and damselfly order Odonata as inferred by mitochondrial 12S ribosomal RNA sequences. Annals of the Entomological Society of America 96(6):693-699.

  • Wells, S.M., R.M. Pyle, and N.M. Collins. 1983. The IUCN Invertebrate Red Data Book. IUCN, Gland, Switzerland. 632 pp.

  • Westfall, M. J., Jr., and M. L. May. 2006. Damselflies of North America, revised edition. Scientific Publishers: Gainesville, Florida. 503 pp.

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