Fas­ci­nat­ing crea­tures

Drag­on­flies and dam­sel­flies are on the wing and pro­vide a fas­ci­nat­ing show on a sum­mer’s day

Canal Boat - - Waterside Wildlife -

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

day.

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