White-faced darter  (Leucorrhinia dubia)

The white-faced darter is classified as Least Concern (LC) on the IUCN Red List (1).

The white-faced darter (Leucorrhinia dubia) is a small, dark dragonfly which, like other members of its genus, is slender and low-flying (2) (3). The male white-faced darter has a thin, black abdomen, marked with red and orange on the upper and lower surface (2) (3). The thorax is also black and marked with broad, red stripes (2). The wings of the white-faced darter are marked with dark brown patches at the base, and the pterostigmas (the dark coloured cells near the tip of the wings) are red-brown (2).

The female white-faced darter is very similar to the male in shape and pattern, but has yellow instead of red markings, and darker pterostigmas (2) (3).

A widespread species, the white-faced darter can be found throughout northern Europe, with its range extending east to Siberia (1) (3). It is present in the UK between the Midlands and north Scotland (3). In France, it is only present in mountain areas (1) (2) (3).

The white-faced darter has very particular habitat requirements in some parts of its range, only inhabiting shallow, peaty pools in the UK (2). In general, this species prefers lowland bogs with deep, acidic pools that have rafts of Sphagnum moss, which it requires to breed (3).

When the white-faced darter is away from its aquatic habitat, it tends to use scrub and woodland for resting and feeding (3).

Like other dragonfly species, the white-faced darter has a complex lifecycle which includes a fully aquatic larval stage (2). 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 (2) (4). The larval white-faced darter tends to hunt during the day, which makes it particularly vulnerable to predation by fish (3). It is, however, known to grow larger spines as an anti-predator response in the presence of fish (5).

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 in order to propel themselves along (4).

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 (2). The development of the white-faced darter larva usually takes two years, although some individuals may complete the lifecycle in less than a year (3). The larva undergoes several moults before finally emerging from the water as the readily recognisable adult dragonfly (2) (6). Emergence of the adult white-faced darters begins in early May and usually occurs in the early to mid morning (3). The flying season of the white-faced darter lasts until mid-August and the adults do not over-winter (2) (3).

After emerging, the adult white-faced darter moves to the nearest suitable wood or scrubland, where it will feed and mature (2) (3). The male will then return to near the water, where it establishes a small territory, although this is not aggressively defended (1) (3). The female white-faced darter prefers to bask on open ground and is seldom found near the water (3). Mating takes place in low bushes or heather, and lasts for about half an hour. After this, the female lays the eggs alone, flying low over shallow pools while dropping the eggs onto the waterlogged Sphagnum moss (2) (3).

Dragonflies are skilled aerial predators, usually catching various small insects on the wing (2). The white-faced darter employs a ‘perch-hunting’ strategy, making forays from a perch when prey is sighted, and then returning to the perch in order to consume the prey (2). Generally only active during the day, this species will return to rest in trees and bushes up to 50 metres from the water at night (2) (3).

Although widely distributed and believed to be generally common, the white-faced darter nevertheless faces a number of threats in parts of its range (1). In the UK, this species has suffered a decline in the last 35 years and is now only found in half of the localities at which it once occurred (3). Much of the original lowland bog habitat in the UK has been destroyed, removing important breeding habitat for the white-faced darter (3). Commercial collection of Sphagnum moss has also been a problem in the past, making habitat unsuitable for breeding and also removing white-faced darter larvae from the bogs (3).

Pollution and eutrophication both alter the water of the peat bogs, changing the pH and plant structure of the white-faced darter’s habitat (3). Future threats to the white-faced darter include climate change, which is causing the range of some species of dragonfly to shift north (3).

There is research currently underway to establish the population size, trends and range of the white-faced darter, although more extensive research will be needed on this species in the future (1). A major factor in the conservation of the white-faced darter is the preservation of its lowland peat habitat. These habitats need to be monitored and managed to prevent the encroachment of scrub and to monitor the quality and levels of the water (3). Habitat creation and restoration are also potential measures in order to ensure the long-term survival of this species (3).

In some counties in the UK, the white-faced darter is included in the Biodiversity Action Plan, which aims to set out detailed plans for the conservation of the biological diversity resources of the UK (3) (7). It is also protected under the Wildlife and Countryside Act 1981 (8).

Find out more on the white-faced darter:

• British Dragonfly Society - White-faced darter
  http://british-dragonflies.org.uk/category/species/leucorrhinia-dubia