Cretan spotted darner (Boyeria cretensis)
|Size||Length: 69 - 71 mm (2)|
Length of abdomen: 45 - 49 mm (2)
Hindwing: 44 - 47 mm (2)
The Cretan spotted darner is classified as Endangered (EN) on the IUCN Red List (1).
Members of the Aeshnidae family are commonly known as ‘hawkers’ or ‘darners’, the latter because the female looks as if sewing when cutting into a plant stem to insert her eggs. This family includes some of the largest and most powerful of the world’s dragonflies. The abdomen of the Cretan spotted darner (Boyeria cretensis) is long, slender, and very narrow just behind the robust thorax, and the wings are almost always clear (3). The larvae are generally very long and slender compared to those of other families (3) (4). This darner species is darkly coloured, much more than its West Mediterranean counterpart, Boyeria irene, and males show only small greyish to yellowish spots on most of abdomen, and have dull emerald-green eyes.
The Cretan spotted darner is highly specific in its habitat requirements, being associated with the upper courses of permanent brooks in shady areas with moderate current and rock pools (1).
Most members of the Aeshnidae family spend much of their time flying and hunting for prey, seldom resting during the day time (4). All prey is caught in flight, and these dragonflies will eat almost any soft-bodied insect that is smaller than them, including other dragonflies (3). After mating, the female deposits her eggs in aquatic vegetation or moist sand (5). The larvae are voracious predators, actively climbing over submerged vegetation to hunt for prey. Like the adults, larvae will eat anything smaller than themselves, including mosquito, damselfly and dragonfly larvae, tadpoles and even small fish. In some species, particularly in those which are well adapted to temporary waters in desert areas, larvae of this family mature in one year or even less, emerging from a split in their skin to become a dragonfly.
If the biology of its western counterpart, B. irene, applies to the Cretan spotted darner, eggs hatch rapidly after oviposition and the larval period spreads over two to three years. The larvae stay preferably within the maze of tree roots submerged in water along river banks, sometimes also at the bottom of streams or within submerged vegetation. Emergence usually occurs at night to minimise the threat of predation, as any emerging dragonfly is highly vulnerable at this time (3).
The Cretan spotted darner is thought to have declined as a result of rapid habitat destruction and degradation, over-exploitation of water by humans, water pollution, eutrophication and deforestation. Climatic changes may also have had a negative impact. As a result, most individuals are now found in small and relatively isolated subpopulations (1).
There are currently no conservation measures targeting the Cretan spotted darner.
Authenticated (18/12/06) by Jean-Pierre Boudot, CNRS, Université Henri Poincaré Nancy I, France.
- Endemic: a species or taxonomic group that is only found in one particular country or geographic area.
- Eutrophication: Excessive growth of aquatic plants that occurs when dissolved nutrients such as phosphorus and nitrogen run-off into lakes and ponds, which also ultimately increases the plant death rate with the result that the bacterial decomposition of the dead plants uses up oxygen. Natural eutrophication may occur gradually, but is often accelerated by run-off of agricultural fertilizers.
- Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Oviposition: egg-laying in insects.
- Thorax: In insects, the three segments between the head and the abdomen, each of which has a pair of legs.
IUCN Red List (March, 2011)
- Dijkstra, K.D.B. and Lewington, R. (2006) Field Guide to the Dragonflies of Britain and Europe. British Wildlife Publishing, Gillingham.
Idaho Museum of Natural History (September, 2007)
- Silsby, J. (2001) Dragonflies of the World. Smithsonian Institution Press, Washington D.C.
Brisbane Insects and Spiders (September, 2007)