The white-faced darter or small whiteface (Leucorrhinia dubia) is a dragonfly belonging to the genus Leucorrhinia in the family Libellulidae, characterised by red and black markings and a distinctive white patch on the head. It is found in wetlands and peat bogs from northern Europe eastwards to Siberia, and the adults are active from around April till September, which is known as the "flight period". It breeds in acidic bodies of water, laying its eggs in clumps of sphagnum moss that provide a safe habitat for larval development. The larvae are particularly vulnerable to predation by fish, and so are usually found in lakes where fish are not present. L. dubia is listed as a species of least concern (LC) by the IUCN Red List, however, it is potentially threatened by habitat destruction, pollution, and climate change.
Description
This species has a predominantly black body, usually in length - the abdomen is long and the hindwing is long. Mature males have striking red and orange markings on the abdomen and thorax which become darker with age, whereas young males and females have pale yellow markings. All individuals have a conspicuous white frons at the front of the head. The wings have a brown patch at the base and noticeable black pterostigma. It may be confused with similar species, including the black darter (Sympetrum danae), ruddy darter (Sympetrum sanguineum) and common darter (Sympetreum striolatum), however is usually distinguishable by its white face patch.
Distribution
This dragonfly's range extends from western Europe to Japan, and it is commonly found in western, northern and eastern Europe at higher altitudes, but is rare in southern Europe and the United Kingdom. In recent decades, this species has been observed as far afield as Russia and China, however the vast majority of sightings have occurred in central and northern Europe. In Britain, the majority of individuals of this species are found in the highlands of Scotland, with key populations located in Inverness-shire and Ross-shire. In England, a few isolated populations occur in Cheshire and Cumbria, where biodiversity action plans have been set up to protect them, and as far south as Chartley Moss National Nature Reserve in Staffordshire. However, when British populations are considered overall, this species has been in decline over the past 35 years.
Habitat
Adult individuals of L. dubia can utilise scrub and woodland habitat for roosting and foraging. The larvae require terrestrial areas of water, such as marshes, wetlands and peat bogs, that generally have vegetation growing at the water's edge. Peat bogs form a particularly important habitat, since they provide acidic conditions necessary for the growth of sphagnum moss, which provides a source of food and shelter.
Life history
Larval stage
Like all other species of dragonfly, the larvae of this species grow by moulting (in which the exoskeleton is shed) several times during development. In the early stages of development, larvae preferentially inhabit sphagnum moss, which may provide a reliable source of food because the moss can trap organic matter that would otherwise sink to the bottom of the water. As well as fish, many waterfowl, amphibians, and other invertebrates will prey upon dragonfly larvae, so the mats likely also provide a safe hiding place from predators. The larvae are able to change colour depending on whether the moss they are inhabiting is brown or green, which would help to visually disguise them from predators. The acidification of ponds and lakes due to airborne pollution may in fact benefit L. dubia and other species that prefer acidic conditions, as this can result in a greater occurrence of sphagnum moss. Larvae will actively forage throughout both the day and night, however have been shown to capture more prey during the night. Larvae will also cannibalise their conspecifics, particularly in the absence of an abundant food source (zooplankton), and can be threatened by predation from other species of dragonflies. Larger individuals will generally cannibalise smaller individuals, and it is believed that this functions as a way of controlling population numbers.