Sombre goldenring (Cordulegaster bidentata)

Also known as: sombre goldenring dragonfly, sombre gold-ringed dragonfly, two-toothed golden-ringed dragonfly
Synonyms: Cordulegaster bidentatus
  
French: Cordulegastre Bidenté
KingdomAnimalia
PhylumArthropoda
ClassInsecta
OrderOdonata
FamilyCordulegastridae
GenusCordulegaster (1)
SizeMale abdomen length: 5.2 - 5.9 cm (2)
Female abdomen length: 5.6 - 6.3 cm (2)
Male hind wing length: 4.2 - 4.5 cm (2)
Female hind wing length: 4.6 - 5.1 cm (2)

The sombre goldenring is classified as Near Threatened (NT) on the IUCN Red List (1).

The sombre goldenring (Cordulegaster bidentata) is a large dragonfly that belongs to a group named for the yellow rings on their otherwise black bodies. In the sombre goldenring, the yellow colouring on the abdomen is somewhat limited in extent and the thorax is marked on the sides with three narrow yellow bands. The ‘occipital triangle’ (the area of the head behind and between the eyes) is black, and there is a black band across the yellow frons (the front, uppermost part of the head). The extent of the yellow markings may vary slightly between individuals (2).

As in other members of the Cordulegastridae family, the sombre goldenring has large eyes that meet at a point on the top of the head. Members of this group also have a long, thin ‘pterostigma’ (a thickened cell on the front edge of the wing), which is usually black (2). The female sombre goldenring is slightly larger than the male, and has a long, black ovipositor at the end of the abdomen (2).

Populations of the sombre goldenring on Sicily have more extensive yellow marks, and have been described as a distinct subspecies, Cordulegaster bidentata sicilica (1). Sombre goldenrings in the southern Balkans also have larger yellow spots than the nominate subspecies (Cordulegaster bidentata bidentata), but the taxonomy of the species as a whole has yet to be clarified (1).

The sombre goldenring appears quite dark in comparison to the related golden-ringed dragonfly (Cordulegaster boltonii). It is also distinguished by having one yellow ring on each segment of the abdomen, whereas the golden-ringed dragonfly often has two (3).

The sombre goldenring occurs in central and southern Europe, from the Pyrenees eastwards to the Carpathian Mountains in western Ukraine (1) (2) (4). The subspecies Cordulegaster bidentata sicilica is found only on Sicily (1) (2).

A rather specialised dragonfly species, the sombre goldenring breeds almost entirely in springs, small mountain torrents, or the upper courses of streams and brooks (1) (2) (5). It tends to prefer tufa springs and small, calcareous brooks (1) (3).

The larvae of the sombre goldenring develop in clear, running water (2), but are restricted to habitats with relatively weak currents (5). The adults are not thought to move far from the breeding areas (2).

The adult sombre goldenring is often seen resting near water, often quite low down and with the abdomen hanging almost vertically (2). Adults are seen between May and August (2) (3), and feed on small insects that fly along the stream (2). Like all dragonflies, the sombre goldenring is an agile predator, and its huge eyes give it excellent vision (6).

After mating, the female sombre goldenring lays eggs into the muddy bottom of a shallow stream or spring, thrusting the ovipositor into the mud to lay the eggs while in flight (2). One female of this species was observed to lay nearly 200 eggs (2). Unlike some other dragonflies (6) (7), the male sombre goldenring does not guard the female while the eggs are laid (2).

The sombre goldenring larvae live buried in mud, sand or gravel on the stream bed, with only the head, front legs and tip of the abdomen exposed. From this hidden position, the larva lies in wait for passing prey (2). Dragonfly larvae are formidable predators which catch their prey by shooting out the lower jaw, or ‘labium’. The labium is armed with hooks, which impale the victim and drag it back to the mouth as the labium is retracted (6) (7).

As a dragonfly larva grows, it goes through a series of developmental stages known as ‘instars’, before emerging from the water and moulting into the adult form. In the sombre goldenring, the larvae develop very slowly and only emerge as adults after about four or five years (2). As in the related golden-ringed dragonfly, the emergence of the adults probably takes place in spring (2). After it has emerged, an adult dragonfly will spend some time feeding and maturing before it breeds (6) (7). However, the lifespan of the adult sombre goldenring is short, lasting only several weeks (2).

Although the sombre goldenring is quite widespread, its rather specialised habitat requirements mean that it only occupies a limited area within its overall range (1). As with many dragonfly species (6) (7), the main threat to the sombre goldenring is the loss and alteration of its breeding habitat (1) (4). In particular, this species is under threat from drought, which is exacerbated by climate change. This is thought to be particularly severe in the southern parts of its range, and some populations have already been lost due to low rainfall and recent hot summers (1). The Sicilian subspecies Cordulegaster bidentata sicilica was always very rare, and the last record from Sicily was in 1981 (1).

The sombre goldenring’s habitat is also being impacted by an increasing demand for water for irrigation and other human uses (1) (8). In addition, some populations of the sombre goldenring have been affected by water acidification due to acid rain or nearby conifer plantations, although this has not affected it everywhere (1).

Dragonflies which are restricted to small brooks and streams, like the sombre goldenring, are particularly vulnerable due to the small size of these habitats. As well as being at greater risk of drying out, their habitat can more easily be destroyed by localised events such as fires, building works, or even the extraction of water by individual farmers (8).

Recommended conservation measures for the sombre goldenring include protecting the streams in which it breeds (1) (4), as well as preserving and restoring nearby forests in order to maintain habitat quality (1).

The adult sombre goldenring is often well hidden and difficult to find, while the sites where the larvae occur are sometimes difficult to locate or access. As a result, this species is still relatively poorly studied and poorly surveyed, and its populations are sometimes overlooked. Further research is needed into the sombre goldenring’s populations and taxonomy (1) (4), and any potential breeding sites of the Sicilian subspecies need to be identified (1).

Find out more about the sombre goldenring and its conservation:

More information on dragonfly and damselfly conservation:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

  1. IUCN Red List (May, 2011)
    http://www.iucnredlist.org/
  2. D’Aguilar, J., Dommanget, J.L. and Préchac, R. (1986) A Field Guide to the Dragonflies of Britain, Europe and North Africa. Collins, London.
  3. Atlas des Odonates de Provence-Alpes-Côte-d’Azur (P.A.C.A.) - Cordulegaster bidentata (May, 2011)
    http://odonates-paca.org/odonates_paca_fiche_detaillee.php?id=55&PHPSESSID=u0lq89rt2u1hec3bcyguk0r67eo3g9in
  4. Ocharan, F.J., Ferreras Romero, M., Ocharan, R. and Cordero Rivera, A. (2005) Cordulegaster bidentata Sélys, 1843. In: Verdú, J.R. and Galante, E. (Eds.) Libro Rojo de los Invertebrados de España. Dirección General de Conservación de la Naturaleza, Madrid. Available at:
    http://carn.ua.es/CIBIO/en/lrie/lrie.html
  5. Leipelt, K.G. (2005) Behavioural differences in response to current: implications for the longitudinal distribution of stream odonates. Archiv für Hydrobiologie, 163(1): 81-100.
  6. Moore, N.W. (1997) Dragonflies: Status Survey and Conservation Action Plan. IUCN/SSC Odonata Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK. Available at:
    http://data.iucn.org/dbtw-wpd/edocs/1997-042.pdf
  7. O'Toole, C. (2002) The New Encyclopedia of Insects and their Allies. Oxford University Press, Oxford.
  8. Kalkman, V.J., Boudot, J.P., Bernard, R., Conze, K.J., De Knijf, G., Dyatlova, E., Ferreira, S., Jović, M., Ott, J., Riservato, E. and Sahlén, G. (2010) European Red List of Dragonflies. IUCN and Publications Office of the European Union, Luxembourg. Available at:
    http://ec.europa.eu/environment/nature/conservation/species/redlist/downloads/European_dragonflies.pdf