Orthetrum coerulescens
Orthetrum coerulescens (Fabricius, 1798)
Local names: Keeled skimmer, Kleiner Blaupfeil, Südöstlicher Kleiner Blaupfeil (ssp. anceps), Beekoeverlibel, Orthétrum bleuissant, Mindre sjötrollslända
Species Information
Description
A common small skimmer around flowing water throughout much of Europe. The light-coloured pterostigma distinguishes this species from Orthetrum albistylum and O. cancellatum. It could be confused with O. brunneum, and often co-occurs with that species, but is slightly smaller, the abdomen is more slender, the pterostigma is longer and yellow rather than light brown. In the males the frons is yellow rather than pale blue. In the mature males covered in light blue pruinosity, the thorax is darker than the abdomen and the yellow base colour shows through. Usually two pale stripes on the front of the thorax are visible, but the sides are uniform in colour.
On the wings, above the radial vein, there is a single row of cells, whereas in O. brunneum the row consists of double cells. The ventation of the wings is entirely black. Wing bases are often suffused with amber but it never has any dark patches near the base as on Libellula species.
Immature and female individuals can be confused with Sympetrum species.
Size
Habitat
The species is most often found at largely unshaded small running waters like streams, runnels or ditches with moderately dense or no vegetation. It also inhabits Sphagnum peat bogs, spring-fed marshes, springs, seepage waters and quarries. In the Mediterranean it is largely restricted to rocky or stony streams and rivers while in parts of central and north-west Europe, including Great Britain, it is confined to shallow open and sunny waters such as ditches, bogs and runnels in quarries and heathlands. The species is most common in lowlands but populations are found up to 1 700 m in the Alps and up to 2 040 m in southern Spain.
Distribution
Orthetrum coerulescens is largely a West Palearctic species and is widespread in Europe and the Mahgreb. It is widespread in the southern two-thirds of Europe , including most of the Mediterranean islands. It becomes progressively scarcer to the north and the north-east with large gaps in its distribution, for example in the British Isles where it occurs mainly in the south and western half, as well as in Poland and the Baltic States. As in the case of O. brunneum, O. coerulescens is much scarcer in the northern areas of eastern Europe. It is widespread in the east of Ukraine but appears to be rare in the south of Russia, and has not been found north of the Caspian Sea or in the well explored southern Urals.
The nominotypical subspecies extends from the Iberian Peninsula to central Europe, mainland Italy, southern Fennoscandia and the British Isles, whereas pure populations of typical O. c. anceps are found from northern Africa to the Middle East, Asia minor, Kashmir, Central Asia, the southern parts of the Balkan Peninsula and southern Ukraine. Intermediate forms between O. c. anceps and O. c. coerulescens are known from the Balkan Peninsula and most Mediterranean islands (Cyklades, Cyprus, Crete, Sicily, Sardinia)
Flight Period
June to September
Behavior
The behaviour of this species is different from O. brunneum and O. nitiderve. It tends to perch on small bushes and on top of low vegetation, unlike the two other that almost always will alight on the bare soil or rocks. It frequently is found far from waters and young individuals has been measured to fly over 20 km from the water they emerged from.
Mature males keep a small territory that is controlled from a lookout perch out in the water or some protruding branch. Often he returns to the same perching spot after dashes. Flight is somewhat jerky, like O. coerulescens. Males can share a territory with Cordulegaster boltonii or Onychogomphus forcipatus.
Oviposition is done in flight, sometimes with the male guarding the female. Larva live in detritus or silty bottom material. Larvae development is two years. Exuviae is usually found low on vegetation in the water.
Conservation Status
Similar Species
Orthetrum brunneum, Orthetrum nitiderve, Orthetrum taeniolatum
External Links
Genus: Orthetrum
Orthetrum is a large genus of dragonflies in the Libellulidae family. They are commonly referred to as skimmers.
Identification
Almost every blue to grey pruinose dragonfly with clear wings will be an Orthetrum male. The combination of a clear base, at most yellow-tinted, and 10-14 forewing cross-veins (thus last antenodal one is complete) is unique for a libellulid.
separation from other genera
Libellula species are similar in venation, stature and pruinosity, but have large dark patches at the hindwing base. Pruinose Leucorrhinia species are dark, with a contrasting white face and also dark hindwing patches. The rather plainly brown females and young males of most Orthetrum species are often mistaken for Sympetrum and Crocothemis. The species in both these genera normally have the last antenodal cross-vein incomplete; Sympetrum has only 6-7 complete forewing antenodal cross-veins, and Crocothemis has large yellow patches at the hindwing base. Especially fresh yellow O. cancellatum and the club-tailed black-and-pale O. sabina superficially resemble gomphids, but their eyes touch each other.
Separation of the species
Some 60 Orthetrum occur in Australia, Eurasia and particularly Africa. The species are often difficult to identify. This is especially true for males, whose markings have become obscured by pruinosity, thus appearing very unlike females and younger males. For convenience, the species can be divided into three groups. In most of Europe, separating O. albistylum from O. cancellatum (group 1) and O. brunneum from O. coerulescens (group 3) will cause the greatest difficulty. In the Mediterranean, two diagnostic species in group 2 and three additional species in group 3 occur. Because up to four species of species group 3 may occur together in Iberia, north Africa or Turkey, identification might be difficult. Examination of the male's secondary genitalia with a hand lens will be most decisive.
| Group | Species |
|---|---|
| Group 1 | O. albistylum O. cancellatum |
| Group 2 | O. trinacria O. sabina |
| Group 3 | O. brunneum O. chrysostigma O. coerulescens O. nitiderve O. taeniolatum |
Behaviour
Active species, often perching on the ground or stones. Male guards the female during oviposition, usually by hovering above her and chasing off rival males.
Family: Libellulidae
The skimmers or perchers and their relatives form the Libellulidae, the largest dragonfly family in the world. It is sometimes considered to contain the Corduliidae as the subfamily Corduliinae and the Macromiidae as the subfamily Macromiinae. Even if these are excluded, there still remains a family of over 1000 species. With nearly worldwide distribution, these are almost certainly the most often seen of all dragonflies.
The genus Libellula is mostly New World, but also has one of the few endangered odonates from Japan: Libellula angelina. Many of the members of this genus are brightly colored or have banded wings. The related genus Plathemis includes the whitetails. The genus Celithemis contains several brightly marked species in the southern United States. Members of the genus Sympetrum are called darters (or meadowhawks in North America) and are found throughout most of the world, except Australia. Several Southern Hemisphere species in the genera Trithemis and Zenithoptera are especially beautiful. Other common genera include Tramea and Pantala.
The libellulids have stout-bodied larvae with the lower lip or labium developed into a mask over the lower part of the face.
The family name may have been derived from the Latin libella which means booklet.