Dragonflies and damselflies are on the wing and provide a fascinating show on a summer’s day
Before dinosaurs roamed the earth you could have seen dragonflies with wing spans as wide as a crow. They are by far the largest insects known to have inhabited our planet and remain a relatively primitive group with transparent, veined wings that beat independently.
Formerly referred to as horse stingers or devil’s darning needles, these magnificent coloured insects do not sting. They belong to the Odonata, meaning toothed jaws and are totally carnivorous.
Most British dragonflies are either hawkers or darters, depending on their hunting methods. Hawkers regularly patrol a stretch of the canal and are generally bigger, with a stronger flight than the darters who, as the name implies, fly quickly out from a perch in waterside vegetation to snatch their prey before returning to the same spot.
They mostly rely on sight for hunting, their huge compound eyes almost touching on the top of the head. Up to 30,000 facets make the eyes extraordinarily sensitive to movement and allow the dragonfly to catch small insects in full flight.
The legs are covered in spine-like bristles and arranged so that they can form a forward-facing basket in flight to net the prey. A dragonfly can cling to a twig or grass stem with its feet but does not walk.
The devilish reputation of the larger dragonflies is replaced by a gentler image for their cousins, the slender, daintier damsels: the alternate name of virgo fly refers to the blue colours worn by the Virgin Mary. Many damselflies are blue, though it is usually the males who are adorned in the brighter colours. With weaker powers of flight they are rarely found far from water, where they spend most of the time resting on vegetation. They get much of their prey by plucking it off waterside plants rather than by chasing it through the air.
Damselflies usually rest with their wings folded up over their backs, a useful way of distinguishing them from the more robust dragonflies who keep their wings extended horizontally on each side. The bulging eyes of a damselfly are more widely separated than those of a dragonfly.
Practically all of the 40 resident species of British dragon and damselflies are on the wing in July. Many species can be recognised by their striking colour alone, though it is not always a reliable guide.
Females often differ in colour or pattern from the males and both sexes change colour as they age: freshly emerged specimens are paler, acquiring their full colours when they are several days old.
Some species, especially the males, develop a whitish or powdery blue bloom in later life. The Common Blue Damselfly is the most widely distributed and bluest all the dragonflies and can be distinguished by a thick blue stripe on the thorax. Females may be blue, brown or green.
Particularly common along canals, they congregate in large numbers in marginal vegetation. Adults are most active when the temperature is highest and flight is generally restricted to sunny weather when the flight muscles in the thorax are sufficiently warm.
They seem to disappear in wet or cool, cloudy conditions, but they are resting, still and well hidden in the vegetation, often hanging under leaves in trees.
You often see pairs of dragonflies flying in tandem before they settle to mate: the male grasps a female by the back of her neck using a pair of claspers at the hind end of his body.
The female curls her abdomen up to the base of his, a spot where sperm is stored, to form a ‘wheel’ and effect fertilisation. Eggs are laid inside plant stems, on submerged weeds, or directly into the water by dipping their abdomens during flight.
Nymphs follow a predatory lifestyle underwater for up to several years before crawling up a plant stem and splitting open to emerge as winged adults. They are fascinating creatures to watch on a warm summer’s