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Cordulegaster boltonii / Golden-ringed dragonfly / Gewone Bronlibel / Zweigestreifte Quelljungfer / Cordulégastre annelé.
Kingdom Animalia
Phylum Arthropoda
Class Insecta
Order Odonata
Family Cordulegasteridae
Genus Cordulegaster
Size Average wingspan: 101 mm
Average length of larva: 35-42 mm
Male length: 74 mm
Female length: 84 mm
The golden-ringed dragonfly is one of Britain’s largest dragonflies, and is the only member of the genus Cordulegaster in the country. Both the thorax and abdomen are black with bright yellow bands, the legs are black with yellow bases and the abdomen is swollen towards the tip. The large green eyes meet in a point at the top of the head. Females can be identified by the presence of a long pointed ovipositor at the tip of the abdomen. As with other dragonflies, the large wings are held outstretched when at rest, not folded back over the body as in damselflies. The large aquatic larva is hairy, and spends most of its life partially buried in the sediment with just the eyes and tip of the abdomen visible. The short head has prominent eyes, and in common with other dragonfly larvae it is armed with fearsome mouthparts.
Range
Common in southern, western and northern England, Wales and Scotland. It becomes rare or even absent in parts of eastern England, the Midlands, eastern Scotland and Ireland. Elsewhere this species is found in central and northern Europe and extends through Asia Minor to India.
Habitat
This dragonfly is found in heathland and moorland habitats. The larvae inhabit small streams that are typically less than 2m wide and overhung with vegetation. They are not found in still water.
Biology
Larvae live partially buried in the sediment, waiting for suitable prey to pass by, which they then ambush. Their development can take as long as 2-5 years, being slower in colder waters. They undergo several moults during their development, which allows them to grow. These aggressive ambush predators feed on insect larvae, snails, tadpoles and even small fish.
When fully developed and metamorphosis has taken place, the larva crawls up bankside vegetation and the adult stage emerges, leaving the shed ‘skin’ of the larval form, known as an ‘exuvia’, behind on the vegetation. Emergence usually takes place at night in order to reduce the high risk of predation. Occasionally, larvae may crawl quite a distance away from the water before selecting an emergence site, and may even climb trees. The newly emerged adults, or ‘tenerals’ do not become sexually mature for around ten days. Like the larvae, the adults are also highly efficient and fearsome predators, feeding on large insects such as damselflies, other dragonflies, wasps, beetles and bumblebees. They are fast, agile and powerful flyers and can be seen on the wing from late May to September.
Although adult males do not defend exclusive territories, they do react aggressively towards other males that they encounter. They patrol lengths of breeding streams at just a few centimetres above the water. When a female is encountered the male will grab her thorax from above with his legs and then manoeuvre so that the he holds her behind her head with claspers located at the tip of his abdomen. At this point the pair is said to be ‘in tandem’ and the male will fly with the female in this position to perch amongst vegetation, where copulation takes place.
Females lay their eggs alone, typically in the morning. The eggs are laid into the sediment of the stream, and the female hovers vertically over the water thrusting her ovipositor downwards into the sediment with a stabbing motion that has been likened to the action of a pneumatic drill. The eggs hatch after a few weeks.
Threats
This species is not threatened.
Conservation
Conservation action has not been targeted at this widespread species.
Source:http://www.arkive.org/golden-ringed-dragonfly/cordulegaster-boltonii/info.html
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