Dwarf damselfly  (Nehalennia speciosa)

Aptly named, the dwarf, or pygmy, damselfly is the smallest damselfly in Europe, measuring just a tiny 23 – 26 mm long (2) (3). The abdomen is slender while the wings are distinctively short and wide (4). Colouration is bluish-metallic green, with a pale blue line on the head between the eyes, a clear distinguishing feature of this diminutive species (5). Like many other members of the Coenagrionidae family (6), female dwarf damselflies come in two distinct colour morphs, being either yellowish-bronze (known as heterochromatic morph) or similarly coloured to the male (known as homeochromatic morph) (5).

Widespread across Eurasia from Germany to Japan, but the westernmost and southernmost severely dispersed and isolated small populations are now all extinct, as well as most of the Scandinavian ones (1) (2).

This habitat specialist is found in small, peaty and marshy lakes and pools, generally of shallow, standing, stagnant water, overgrown with vegetation such as sphagnum mats, sedges and fens (1).

Odonata species start their life as aquatic larvae or nymphs, passing through a series of developmental stages or ‘stadia', undergoing several moults as they grow. This larval period can last anything between three months and ten years, depending upon the species. 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, when individuals normally develop their full adult colour (7).

In the dwarf damselfly, larvae grow generally over one year, but 10 to 20% do not reach emergence until their second year. The main flight period for the adult of this species is from the beginning of June to the end of July, during which time they must mate (5). Adults remain usually perched for a long time without flying and prefer the thin leaves of some sedges such as Carex limosa and C. lasiocarpa on the fringe of peaty pools and peat bogs, in order to detect any threat on each side. From time to time, they feed on small flying insects. Some isolated specimens have been found about 10 km away from their reproductive site and the species is able to colonise new water bodies. Females lay eggs (oviposit) in plant tissues, using their ovipositor to cut a slit in the tissue into which they lay their eggs.

The dwarf damselfly is threatened by the ongoing decline of suitable habitat due to drainage of wetland areas, extreme weather events and climatic changes (global warming). Pollution and overgrowth of habitats also threaten the survival of this species, particularly as a result of eutrophication caused by an increased run-off of fertilisers and nutrients into the water from nearby deforested or agricultural land (1). As a habitat specialist, the dwarf damselfly is extremely vulnerable to changes within this habitat.

This tiny damselfly is protected by law in some areas of its range, such as in Poland, and can be found in a number of national parks and reserves (8).

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