Why heathland pools are so good for odonates

A heathland pool is often not much to look at — a dark, peat-stained hollow among the heather, ringed with rushes and sphagnum. That is exactly why it works. Because the water is shallow, dark-bottomed and low in nutrients, it warms quickly on a sunny morning and holds that warmth into the afternoon. Few fish can survive in such pools, so the underwater nymphs, which spend one to three years as voracious aquatic predators, are not being picked off constantly. Add plenty of marginal vegetation for emerging, perching and roosting, and you have some of the best dragonfly and damselfly habitat in Britain.

The result is that a pool no bigger than a tennis court can hold six or seven breeding species, including heathland specialities you will struggle to find elsewhere.

Where to look around the pool

The open water is only part of the story. Walk the edge slowly and read the structure.

• Sheltered, sunlit bays. Anything facing south or south-west and screened from the wind will be patrolled first, often from mid-morning.
• Sphagnum rafts and floating mats. These are egg-laying sites for emerald damselflies and, on the wettest mires, for small red and scarce blue-tailed damselflies.
• Emergent rush and sedge stems. The vertical stems are perches, territorial vantage points, and the places where nymphs climb out to emerge. Look for the empty brown husks, or exuviae, left behind.
• Bare wet peat and muddy margins. Keeled skimmers and black darters often bask flat on the ground here, where the surface is warmest.
• Seepages and boggy runnels. Small trickles feeding the pool are goldmines for golden-ringed dragonflies and beautiful demoiselles.
• Dry banks, heather and gorse edges. Mature dragonflies retreat here to feed and roost when the pool is busy or the weather turns.

Telling dragonflies and damselflies apart

Damselflies are slender, with a weak, fluttering flight that keeps them low in the vegetation. Their eyes are set wide apart, like beads on either side of the head, and most species fold their wings along the body when they settle — the exception being the demoiselles, which hold theirs loosely open. Dragonflies are bulkier and far stronger on the wing, with eyes that touch or nearly touch across the top of the head, and they rest with wings held flat and open.

If you can only get a glimpse, watch the flight line. Damselflies drift and dab; dragonflies patrol, chase and hover with real purpose.

Species worth knowing

Chasers and skimmers. The broad-bodied chaser is chunky and flattened, the male powdery blue with dark bases to the wings. The four-spotted chaser is browner, with a dark spot on each wing and a habit of returning to the same rush stem. The keeled skimmer is the classic heathland pool species: the male is blue-grey with a pale stripe down the abdomen, the female ochre, and both fly low and fast over boggy ground from June to August.

Darters. The black darter is small and dark, the male almost entirely black with a few yellow spots and a red-tinted abdomen, and it favours the wettest, most acidic pools from July into September. Common darters appear later in the season and perch on bare ground, often tilting their abdomen towards the sun.

Hawkers. Emperors patrol high and fast over open water in summer. Common and southern hawkers hunt along scrubby edges, and both have a habit of hovering close if you stand still. The golden-ringed dragonfly, our longest species, works the small runnels and flushed ditches that thread through heathland.

Damselflies. Large reds are the first out, often in April, with black legs and a dull red body. Small red damselflies are heathland specialities — brighter, daintier and with red legs. Azure and blue-tailed damselflies are the common blues of any pool, while emerald damselflies shimmer metallic green and prefer to sit in dappled shade. On the wettest mires, watch for scarce blue-tailed damselflies, low and wary among the rushes.

Timing, weather and seasons

The season runs from late April to early October, with the peak from mid-June to mid-August. Warm, still, bright days are best, but a light breeze is no bad thing — it pushes insects onto sheltered edges where you can watch them properly. Go out after a warm night rather than a cold one. Early mornings are for emergence, when nymphs climb stems and split their skins; midday to mid-afternoon is for territory and egg-laying; the last hour of sun is for feeding and roosting. A warm, humid evening can produce spectacular hunting flights over the heather.

Getting close without disturbing them

Casting a shadow over a perched dragonfly will send it away instantly, so approach with the sun behind or to the side of you, not in front. Move slowly, keep low, and pause between steps. Once you have found a perch an insect keeps returning to, stop a few metres short and simply wait: most will come back within a minute or two and settle exactly where they were.

• Close-focusing binoculars are more useful than a long lens for identification in flight.
• Learn your exuviae — they are a reliable, non-intrusive record of breeding.
• Note the date and grid reference for any heathland speciality, and send records to your county recorder; that data protects these pools.
• Never net or handle unless you are part of a licensed survey.

A single heathland pool, watched patiently through one summer, will teach you more about dragonflies than a dozen photographs. Take a chair, a pair of binoculars and an hour of sunshine, and let the pool come to you.