Frey's damselfly  (Coenagrion hylas freyi)

Europe's rarest damselfly, Frey's damselfly is currently known only from a small alpine region in Austria (1). With its conspicuous blue-and-black colouration, Frey's damselfly is typical of the Coenagrion genus, commonly known as ‘northern bluets' (4). Both sexes can be easily recognized through the two lateral black lines running along the sides and underside of the whole abdomen, and by the occurrence of black markings on the sides of the thorax at the base of the hindlegs, two characters shared with only the Scandinavian and Siberian C. johanssoni (2). As in many northern bluets, females come in two forms. Blue, green and black ‘heterochromatic' females show a peculiar triangle- or diamond-shaped black pattern on the dorsal part on their second abdominal segment and are easily distinguishable from males; others (homeochromatic forms) share a common U-shaped black pattern on the dorsal part on their second abdominal segment with males (2).

Frey's damselfly is currently only known from the Lech and Inn rivers watersheds, Tyrol, Austria, having become extinct in Germany in 1967, just a few years after its discovery there in 1952 (1).

Found in clear, shallow, mountain lakes densely bordered with sedges and sometimes with areas of slow running water, such as from incoming streamlets, between 800 and 1600 metres above sea level (1) (2).

Dragonflies and damselflies (Odonata) start their life as aquatic larvae or naiads, passing through a series of developmental stages or ‘stadia', undergoing several moults as they grow. Before the final moult (emergence), metamorphosis occurs in which the larvae transform into the adult form. After emergence, adults undergo a pre-reproductive phase known as the maturation period, and this is when individuals normally develop their full adult colour (5). In C. hylas, larvae grow over two years. Adults of this species are mainly active from about 10:30am to 14:30pm from mid-May to mid-August, during which time they must mate (2) (6). Males don't seem to defend territories. Females lay eggs (oviposit) in plant tissue, using their ovipositor to cut a slit in the tissue into which they lay their eggs.

With only seven small reproducing populations out of 14 localities recorded over a restricted area of Austria (around 500 km²), Frey's damselfly is the rarest damselfly in Europe. In Germany, the damselfly is now regionally extinct. Threats to this subspecies are thought to include water pollution, changes in water regimes, eutrophication, the introduction of fish and climatic change. This damselfly appears to be a habitat specialist, dependant upon a complex combination of mountain lakes with aquatic vegetation and areas of slow moving waters, which makes it very sensitive to changes within this habitat (1) (6).

Frey's damselfly is listed on Annex II of the EU Habitats Directive and Annex II of the Bern Convention (2). There is an urgent need to control the water regimes and levels of water pollution that impact this rare subspecies, if Europe's rarest damselfly is to have any chance of survival (1).

Authenticated (18/12/2006) by Jean-Pierre Boudot, CNRS, Université Henri Poincaré Nancy I, France.