|scientific name Coenagrion |
common name Eurasian bluets
Marshes, fens, ditches, small ponds, slow moving streams – generally, still water with emergent vegetation.
Adults fly during the summer months in temperate regions but year round in the tropics.
The Eurasian bluets are a diverse group with approximately forty species worldwide. Most Coenagrion are Old World species but three occur in North America (C. angulatum, C. interrogatum, C. resolutum) (Westfall and May 1996). The North American species are emphasized here but the diagnosis is general. The Eurasian bluets most closely resemble the American bluets (genus Enallagma) but are also similar to the forktails (genus Ischnura). Adult female Eurasian bluets are easy to distinguish, as they do not have a spine on the underside of the eighth abdominal segment like that of American bluets or forktails (Walker 1953). Males have less obvious characters to distinguish them. Coenagrion males have a blue shoulder stripe near the top of the thorax; the stripe is broken to form an exclamation point in most individuals (Westfall and May 1996). Additionally, male Eurasian bluets have a filamentous extension to the end of the penis (on anterior margin of the third segment) that does occur in the American bluet or forktail genera (Walker 1953). Other, more complex, distinguishing characters for males are wing venation and the appendages of the terminal abdominal segment (caudal appendages) (Westfall and May 1996).
Larvae of Eurasian bluets are even more difficult to distinguish from American bluet or forktail larvae then are the adults. Coenagrion larvae are of average stature with the posterior margin of the head rounded and eyes not very prominent (Walker 1953). They have unbanded gills that are fairly broad with pointed tips (Westfall and May 1996).
There is no general life history information available for Eurasian bluets. Due to their cosmopolitan distribution there are differences in the number of generations per year between temperate and tropical regions. Norling (1984) demonstrated that populations separated by nine degrees of latitude in Sweden could have up to a four-fold difference in generation time. Furthermore, there were differences in generation time within local populations. Tropical species also have the opportunity to fly year round where temperate species only fly in the summer months. Generally, the North American Coenagrion require one year to complete their life cycle but may take two (Baker and Clifford 1981). Sawchyn and Gillott (1975) performed a detailed study on the biology of prairie and taiga bluets in Saskatchewan. Females lay soft, creamy-white eggs during June and July in cuts made in living, aquatic plant tissue. Embryonic development takes 2 to 3 weeks. Larvae develop rapidly and near completion by October. Larvae over-winter in one of the final three stages (instars) of development frozen in the ice that forms in their shallow habitat. The larvae intentionally place themselves where they become embedded in the ice but do not freeze. The larvae remain dormant until April when the ice melts and then continues development. This adaptation may not be necessary in all parts of the North American range. Larvae leave the water to become adults by mid-June. Newly emerged adults disperse from the larval habitat to feed and mature. Maturation requires about 1 week and mating occurs away from the water, oviposition occurs within 2 weeks of adult emergence. Oviposition occurs with the male still attached to the female. Eggs are may be deposited above or below the water surface on floating or emergent vegetation.
Although some species may occur low in abundance, only one Eurasian bluet is considered vulnerable. Coenagrion mercuriale, the southern damselfly, is found in the south and west of Europe and is threatened throughout much of its range due disappearance of its specialized habitat (Rouquette and Thompson 2005).
Eurasian bluets, like all damselflies, are predators. Adults feed predominantly on flies (e.g. midges). Larvae are also predaceous; they are opportunistic generalists that engulf their prey. Larval diets include zooplankton, fly larvae, other odonate larvae, assorted invertebrates and even immature vertebrates (Baker and Clifford 1981, Nelson and Thompson 2004).
Eurasian bluets have a cosmopolitan distribution and can be found in all parts of the world.
There are approximately 40 species of Eurasian bluets worldwide. Only 3 species occur in North America and all of these can be found in Alberta (prairie, subarctic and taiga bluets).
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