Blue basker (Urothemis edwardsii)

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Blue basker
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Blue basker fact file

Blue basker description

KingdomAnimalia
PhylumArthropoda
ClassInsecta
OrderOdonta
FamilyLibellulidae
GenusUrothemis (1)

A stout, medium-sized dragonfly, the blue basker (Urothemis edwardsii) is an attractive species with deep blue and black markings (2). The blue colouration of the male’s abdomen is overlain with a distinctive ladder-like pattern of black along the upper surface. The blue basker’s head is shiny black with light grey patches in places, and the eyes are generally black. Its hindwings are marked at the base with a black to purplish patch, which is outlined with an amber halo. The pterostigmas (the dark coloured cells near the tip of the wings) are light yellowish with a thin, black margin along the front edge (2).

Although similar in size to the male, the female blue basker differs in colour. Instead of blue, the female is light yellow to greyish-brown, overlain with dark brown markings. The hindwing patch is much less intensely coloured than in the male, and the wing tips of the female are also marked with dark amber (2).

Synonyms
Libellula edwardsii, Urothemis edwardsi hulae.
Size
Length: 40 - 42 mm (2)
Hindwing length: 33.5 - 35 mm (2)
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Blue basker biology

Like other dragonfly species, the blue basker has a complex lifecycle which includes a fully aquatic larval stage (5). As larvae or ‘nymphs’, dragonflies are effective sit-and-wait predators with the fascinating feature of being able to fire out the lower portion of the mouth, known as the ‘mask’, in order to grasp passing prey (5) (6). As well as being able to walk, dragonfly larvae are able to move through the water by jet propulsion, expelling water from a specialised rectal chamber to propel themselves along (5).

The total length of time spent in the larval stage varies between dragonfly species, with some species spending a few months and others several years as a larva (5). The larva undergoes several moults before finally emerging from the water as the readily recognisable adult dragonfly (5) (6). The flying season of the adult blue basker is between December and May (2).

Reproduction in dragonflies generally involves very little courtship behaviour, and begins with the male grasping the female by the back of the head with claspers at the tip of the abdomen (5). Mating then takes place in the air, on the ground or among vegetation, with the length of the process varying greatly between species (5).

Dragonflies are skilled aerial predators, typically feeding on small insects caught on the wing (5) (6). Members of the Libellulidae family tend to hunt from perches, pursuing prey once sighted before returning to the perch to consume it (5). The blue basker tends to perch on reed tips near the water, or on grass stems, twigs or bushes when away from the water (2).

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Blue basker range

Widespread in tropical Africa, the blue basker mainly occurs south of the Sahara (1) (3). Its western range includes Mauritania, Senegal, Gambia and Sierra Leone, extending eastwards to Egypt, Sudan and Somalia (1). The southern extent of its range includes South Africa (1). A relict population of the blue basker exists in North Africa, in the north of Algeria (3).

The blue basker also occurs in the Middle East, including Arabia and Oman. This species was previously found in Palestine, where it is now believed to be extinct (3).

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Blue basker habitat

A freshwater species, the blue basker can be found in or around reedy pools, marshes and lakes, as well as slow flowing, almost stagnant, streams, rivers and floodplains (1) (2) (3). It can also occasionally be found in grasslands (2), and may also sporadically colonise high-elevation pools if conditions are suitable (4).

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Blue basker status

The blue basker is classified as Least Concern (LC) on the IUCN Red List (1), and as Critically Endangered (CR) on the IUCN Mediterranean Red List (3).

IUCN Red List species status – Least Concern

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Blue basker threats

Although the blue basker is widespread in tropical Africa, the small population remaining in North Africa is facing increasing risk of extinction (1) (3). Two of the three populations that existed in Algeria are now extinct, and the remaining population is thought to number fewer than 40 breeding individuals, though this population may also now be extinct (3). Destruction of the blue basker’s habitat through eutrophication, water extraction and loss of the aquatic vegetation are thought to have contributed to this species’ decline in Algeria (3).

In general, dragonfly species are facing a number of threats globally, including pollution, the introduction of invasive alien species, the destruction of their aquatic habitat and the potential future impacts of climate change (2) (4).

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Blue basker conservation

A species action plan is urgently needed in order to conserve the remaining North African population of the blue basker (3). This species may benefit from general conservation plans for Lac Bleu, the location of the remaining Algerian population, and from future research and monitoring (3).

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Find out more

Find out more about the blue basker and other threatened species of the Mediterranean region:

Find out more about species in the Mediterranean Basin:

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Authentication

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

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Glossary

Abdomen
In arthropods (crustaceans, insects and arachnids) the abdomen is the hind region of the body, which is usually segmented to a degree (but not visibly in most spiders). In crustacea (such as crabs), some of the limbs attach to the abdomen; in insects the limbs are attached to the thorax (the part of the body nearest to the head) and not the abdomen.
Eutrophication
A process in which a water body is enriched with excessive nutrients (such as nitrogen and phosphorus) resulting in the excessive growth of aquatic plants and the depletion of oxygen, creating unfavourable conditions for other organisms, such as fish.
Invasive alien
Species introduced deliberately or unintentionally outside their natural habitats where they have the ability to establish themselves, invade, outcompete natives and take over the new environments.
Larva
Immature stage in an animal’s lifecycle, after it hatches from an egg and before it changes into the adult form. Larvae are typically very different in appearance to adults; they are able to feed and move around but are usually unable to reproduce.
Moult
In insects, a stage of growth whereby the hard outer layer of the body (the exoskeleton) is shed and the body becomes larger.
Nymph
Stage of insect development, similar in appearance to the adult but sexually immature and without wings. The adult form is reached via a series of moults, and the wings develop externally as the nymph grows.
Thorax
Part of the body located between the head and the abdomen in animals. In insects, the three segments between the head and the abdomen, each of which has a pair of legs.
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References

  1. IUCN Red List (December, 2011)
    http://www.iucnredlist.org/
  2. Samways, M.J. (2008) Dragonflies and Damselflies of South Africa. Pensoft Publishers, Sofia.
  3. Riservato, E. et al. (2009) The Status and Distribution of Dragonflies of the Mediterranean Basin. IUCN, Gland, Switzerland and Malaga, Spain. Available at:
    http://cmsdata.iucn.org/downloads/mediterranean_dragonflies_en_web.pdf
  4. Samways, M.J. (2010) Impacts of extreme weather and climate change on South African dragonflies. BioRisk, 5: 78-84. Available at:
    http://www.pensoft.net/J_FILES/2/articles/843/843-G-1-layout.pdf
  5. Gibbons, B. (1986) Dragonflies and Damselflies of Britain and Northern Europe. Hamlyn Limited, London.
  6. O’Toole, C. (2002) The New Encyclopedia of Insects and their Allies. Oxford University Press, Oxford.
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Image credit

Blue basker  
Blue basker

© Jan Van Der Voort

Jan Van Der Voort
Antoon Wolfsstraat 24/1
Schoten
2900
Belgium
janvandervoort64@gmail.com

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