The riverbank as a summer classroom

There are few better ways to spend a warm afternoon than leaning on a riverbank rail, watching the low sunlight catch the wings of something fast and bright. Britain has around 40 species of dragonfly and damselfly, and a good stretch of slow-moving river, canal or flooded gravel pit can hold a dozen of them at the peak of summer. The trick is knowing what to look for, rather than simply admiring the blur.

Most confusion comes from trying to identify these insects in flight. Slow down, watch where they settle, and the whole group opens up.

First, split the two families

Everything you see will belong to one of two groups, and the difference is easy to spot once you know it.

• Damselflies are slender and delicate. At rest they fold their wings back along the body, like a closed book. Their eyes are set wide apart on either side of the head.
• Dragonflies are bulkier and stronger. At rest they hold their wings out at right angles, like an aircraft. Their eyes are huge and usually touch in the middle.

Flight tells you a lot too. Damselflies flutter weakly among the stems; dragonflies patrol, hover and dart with real purpose.

Early summer: demoiselles and blue damselflies

From late May the first showy species appear. The Banded Demoiselle is the one most people notice, and it is genuinely hard to miss. The male is metallic blue-green with a broad dark band across each wing; he flutters over the current like a tiny scrap of oiled silk. The female is a soft metallic green with pale, green-tinted wings. Both are strongly tied to slow-flowing rivers and neutral to alkaline water.

On faster, more acidic streams in the west and north, look for the Beautiful Demoiselle. The male is darker, with almost entirely dark wings, which makes him look far blacker in flight.

The small blue damselflies are the ones that trip people up. The Azure Damselfly carries a distinctive black U or thistle shape on the second segment of the abdomen. The Common Blue Damselfly lacks that mark, is bluer overall, and is genuinely the most abundant of the group. The Blue-tailed Damselfly is easy: an almost entirely black abdomen with one bright blue segment near the tip. The Large Red Damselfly is the earliest of the lot, often on the wing from April, and its deep red body is unmistakeable.

Mid-summer: hawkers on patrol

By late June the riverbank belongs to the hawkers. These are the big, fast dragonflies that cruise a fixed beat up and down the water, often coming close enough to identify without binoculars.

The Emperor Dragonfly is Britain's largest, a powerful blue-green insect with a bright apple-green thorax. Males patrol low over open water, chasing off rivals, from late May into August. If something chases a kingfisher, it is probably an Emperor.

The Brown Hawker is unmistakable: rich chocolate-brown wings, a golden-brown body, and a habit of flying high and late into the evening. The Southern Hawker is green and black with blue spots near the tip of the abdomen, and it is famously nosy, often hovering to inspect the person watching it. The Migrant Hawker arrives later, from August, and is smaller and daintier, with blue and yellow markings and a fondness for feeding high among trees before dropping to the water.

On upland streams, keep an eye out for the Golden-ringed Dragonfly, a black insect banded with yellow and finished with striking green eyes. It hunts along shaded, rocky burns rather than lowland rivers.

Late summer: chasers, skimmers and darters

As August wears on, the emphasis shifts from patrol to perch. This is the best time for close study, because these species sit still and let you look.

• The Four-spotted Chaser is brown and amber, with dark spots at the base of each wing, and perches conspicuously on rush tips.
• The Broad-bodied Chaser is stubby and flattened, with broad dark patches at the wing bases; males turn powdery blue, females golden-brown.
• The Black-tailed Skimmer likes bare gravel and bare earth, and the male's pale blue abdomen ends in a smart black tip.
• The Common Darter is the small red one that lands on fence posts, stones and occasionally your shoulder. The Ruddy Darter is similar but deeper red, with all-black legs and a slightly clubbed abdomen.

Fieldcraft: getting a proper look

Patience beats equipment every time, but a few habits will transform your success rate.

• Walk slowly and stop often. Hawkers in particular respond to sudden movement.
• Approach perched insects from the shaded side and keep your silhouette low.
• Look for regular perches: dead stems, fence posts, gravel spits and sunlit leaves.
• Early morning and late afternoon are best for perching dragonflies; midday heat sends them airborne.
• Sheltered, sunny stretches out of the wind hold far more insects than exposed banks.
• Close-focusing binoculars, or a phone camera held at arm's length, will confirm details such as leg colour and wing spots.

Once you can separate the two families, note the flight season and find the perch, most common riverbank species fall into place. It is one of the most rewarding skills a summer walker can pick up — and it costs nothing but a little quiet standing.