Important habitats for dragonflies and damselflies in Scotland
The wide range of environmental conditions throughout Scotland has resulted in a landscape where wetlands occur at all altitudes and latitudes. These vary enormously from fast-flowing streams on steep hillsides, to bogs in moorland and woodland, as well as meandering streams, lochans and ponds, both artificial and natural. From pools at altitudes of up to 600m to brackish rock pools at sea level - and all the wetlands in between - there is an almost endless variety of habitats to support Scotland’s unique dragonfly and damselfly fauna.
Temperature plays an important part in the distribution of these insects. The Gulf Stream warms sheltered parts of the west coast and Morayshire, enabling species to occur there that would not survive harsher weather conditions. At the other extreme, the cool, drier ‘continental’ climatic conditions of the glens of Deeside and Speyside are preferred by our rarest damselfly, the Northern damselfly Coenagrion hastulatum.
Acidic bogs in moorland are favoured by several species, and one of our special hawker dragonflies breeds only in such habitats. Others variously use peaty lochans, or shallow acid bogs or deep bog pools in woodland. Runnels leading from or into bog systems are often less acidic, and support one of Scotland’s scarcest dragonflies. Sheltered, rich, lowland lochs with tall-emergent vegetation attract yet another of our ‘specialist’ Hawker species, and a few gentle streams in broad river valleys of the south and west have populations of the only truly river-dwelling Odonata in Scotland – the demoiselle damselflies.
It is worth noting that the habitat requirements for a particular species in Scotland may not always be the same as in England, or elsewhere in Europe. Such differences may perhaps reflect adaptation to ‘edge of range’ situations. Equally however, some species may occupy a similar unique habitat type wherever they occur. In all the situations where the rarer Scottish species breed, populations of our more widespread, less specialised, species will also be found.
Forest bogs and lochans
Levels and depressions in acid, wooded ground from Spinningdale on the Dornoch Firth in north-east Scotland and throughout the country to Argyllshire and the south-west tend to have bogs dominated by the acid-loving Sphagnum mosses.
In the finest of these areas the bogs are amongst ancient woodland - predominantly of Scots Pine and Birch. This is especially so in some of the magnificent valleys running west of the Great Glen – such as Glen Affric and Glen Strathfarrar. Similar habitats occur between the Beinn Eighe massif and Loch Maree in Wester Ross, as well as in Speyside in the east and to a lesser extent in Perthshire and Stirlingshire, and right down through Argyll.
The Northern emerald Somatochlora arctica lives in such areas and, apart from a tiny colony in Ireland, the Scottish populations are unique in the British Isles. Although it has a wide distribution there, it is difficult to find. The shallow bogs and runnels it breeds in can be very small. On emergence, the flying insect immediately heads for the treetops and does not return to a bog until seeking a mate. Males usually fly only in bright sunshine in the warmer part of the day. Despite emerald-green eyes, the female can be difficult to spot as she flies from place to place, distributing her eggs over a wide area and she may disappear from a site for an hour or more at a time.
In lochans in some wooded glens one or both of the two other Emerald dragonflies occur. Both Downy emerald Cordulia aenea and the Brilliant emerald Somatochlora metallica have very disjunct British distributions, and the Scottish populations are of special ecological interest. Of the two, the Brilliant tends to be in lochans at slightly higher altitude, and in Argyllshire even in treeless, exposed sites, whereas the Downy emerald is found in wooded sheltered situations. Both species are fast-flying – the blackish colouration of the Downy, and rather ‘club-tailed’ appearance of the male, help to identify it.
Small deep Sphagnum-rich pools in woodland bogs, support the White-faced darter Leucorrhinia dubia. An attractive, rather weak-flying species, its exacting habitat-requirements make Scotland the main centre of its British distribution. It occurs from Applecross in the west to Grantown-on-Spey in the east, in the glens of western Scotland and as far south as Perthshire and Rannoch Moor.
In Speyside, Aberdeenshire and Perthshire the sheltered, still waters of lochans that have dense emergent vegetation of sedges are home to Scotland’s rarest and most endangered Odonata species, the Northern damselfly Coenagrion hastulatum. It occurs nowhere else in the British Isles, and seems dependent on the particular micro-climate of these areas. All of its few known long-established sites are lochans where a constant water depth of 30cm or more is maintained by a dam, with continuous inflow from higher ground.
The Odonata interest of moorlands is mainly in the grass, sedge and bog moss dominated landscapes, rather than the iconic, managed heather-clad hills, which are often too steep and too dry.
Flushes in moorland may show subtle differences in their acidity and other characteristics. In the west of Scotland one tiny acidic patch of bog, the only area around with obvious Sphagnum, sufficed for the emergence of a small number of the Northern emerald; close by, a narrow seepage channel about 15cm deep had larvae of the Keeled skimmer Orthetrum coerulescens. The latter is very scarce and mainly confined to milder climates of the west. It seems to need the influence of slightly mineralised water, and sometimes uses runnels or deltas formed when run-off from a hillside fans out on reaching flatter ground.
The Golden-ringed dragonfly Cordulegaster boltonii also patrols such runnels and seepages. It breeds in running water, and in Scotland may use anything from roadside ditches to quiet streams several metres wide, if flow-rate and stream-bed conditions are suitable. It is widespread in the Highlands, though much scarcer in eastern Scotland.
Highly acidic bog-pool complexes in open exposed situations, sometimes forming ‘patterned mires’, are another distinctive element of moorlands. This habitat supports the Azure hawker Aeshna caerulea, which is found nowhere else in the British Isles. It occurs from sea level to altitudes of 500m or more. Breeding sites are often tiny, shallow bog-pools. Ideal pools may be only about. 20cm deep, over a thick, soupy substrate of peaty detritus. Deeper water is preferred by the Common hawker Aeshna juncea, which may share the same habitat. Small bog-pools get noticeably warm on a dry hot summer’s day and are very susceptible to drying out. This potentially disastrous effect has been observed in recent years in many parts of the Azure hawker’s range. Its populations stretch from Forsinard in the Sutherland ‘Flows’, down to Perthshire and Rannoch Moor, with an outpost in Galloway. For the reasons given above, no one bog pool could be considered as a ‘site’ for this species: a whole complex of such pools is required to sustain a population.
The Black darter Sympetrum danae also breeds in such situations, as well as in a variety of acidic woodland, moorland flushes and peaty lochans, and is well distributed throughout Scotland. A summer-emerging dragonfly, it may attain large numbers at favourable sites.
On lower ground on the western fringes, from Cape Wrath to the Hebridean islands and Kintyre, the so-called Highland darter Sympetrum nigrescens has long been known. The males are red-bodied as in the Common darter. It may simply be a heavily marked form of that species but has been claimed to be specifically distinct. More ‘typical’ Common darters have only recently spread north throughout much of Scotland and may now occur in many of the same areas. Until further scientific study resolves the matter, both ‘species’ in Scotland are best referred to as Common darters.
Rivers and streams of the south and west: domain of the Demoiselles
Even in the warmer conditions of southern Britain, rivers support only a few dragonfly and damselfly species. In Scotland, river head-waters are often in the hills, where they are regularly fed by relatively high rainfall, and often snow melt-water in winter. The resulting powerful flow and relatively low water temperatures for a large part of the year, tend to make most of these water-courses unsuitable for warmth-loving Odonata. Nonetheless, a few rivers and streams in sheltered low-lying areas of southern and western Scotland hold the spectacular demoiselle damselflies, at their most northerly sites in Britain.
Shallow, gravelly streams in the wooded lowlands of Argyll and Inverness (including the islands of Isla, Jura and Mull), are home to scattered colonies of the Beautiful demoiselle damselfly Calopteryx virgo. The jewel-like, violet-iridescent wings and body of the male give it the appearance of being an exotic, tropical insect. Males need overhanging vegetation on which to perch to look out for passing females. When one appears, they fly out and use rapid movement of their broad, butterfly-like wings in a courtship flight, enticing the female to mate near a suitable egg-laying site. Such activity is fascinating to watch and the demoiselles are two of the only three British Odonata to exhibit true courtship behaviour.
The closely related Banded demoiselle Calopteryx splendens behaves in much the same way, though it prefers sluggish silty rivers in less shaded situations. Its breeding presence in Scotland was only discovered in 2004, until when the limits of its UK range were thought to be on the south side of the Solway, and in Northumbria. It now seems that it is well-established on one small, south-flowing, coastal river in Kirkcudbrightshire, though how long it has been there is not known. This warm, sheltered area has few similar rivers, so whether the species could ever extend far into Scotland is debatable.
Slow-flowing backwaters of rivers and streams may sometimes be used by species normally found only in still waters; the Golden-ringed dragonfly discussed earlier prefers boggy moorland streams and runnels, but does sometimes use edges of larger watercourses.
Richer lowland lochs
The mild, coastal lowlands of Galloway and Argyll are home to ‘outpost’ populations of dragonflies and damselflies which are scarce or of limited occurrence much further south in northern England.
Sheltered, shallow lochs, which are not too acid and are fringed with fens of Common reed Phragmites australis or Common club-rush Schoenoplectus lacustris (also, rarely, Great fen-sedge Cladium mariscus), support the Hairy dragonfly Brachytron pratense. Its name refers to the especially hairy thorax, believed to help conserve heat in the cool, early-emergence season. The species appears during May and is rarely seen after early July. Its distinctive larvae like to cling to the underside of litter of the tall-emergent plants, and will often ‘play dead’ if disturbed or handled.
The same habitats contain important colonies of the Variable damselfly Coenagrion pulchellum, a species which is rare and vulnerable in the UK north of Wales. Its similarity to the more widespread Azure damselfly often leads to confusion over identifications, and an expert opinion is needed to confirm its presence at unrecorded sites. The “Variable” lives up to its name and the markings on both thorax and abdomen can sometimes be difficult to interpret. The situation is not helped when both species occur at the same site!
Both Hairy dragonfly and Variable damselfly species extend as far north as the Black Lochs, near Oban. Because of the range of habitat conditions here (from neutral to acid in character), this area has the highest number of Odonata species recorded for anywhere in Scotland - 14. The Hairy dragonfly has recently been found at other sites near the Argyll coast where the aspect is sheltered and east-facing.
Another species of less acid waters, the Southern hawker Aeshna cyanea, has a scattered occurrence at these westerly sites and northwards to the lowlands around Inverness. Elsewhere in Britain and Ireland it is a frequenter of woodland pools, and the most familiar dragonfly of garden ponds. The species is now seen with increasing frequency in the south of Scotland. A recent discovery of larvae in tiny, brackish, rock-pools not far above the tide line on the east coast of Mull, shows the adaptability of this species at the edge of its range!