Large winged insects, with very elongate bodies; usually brightly
coloured. Eyes very large and prominent. Antennae small and filamentous. Mouthparts for biting, with mandibles strongly
toothed (from which the order gets its name). Two pairs of narrow, shiny, membranous wings, with an intricate network of veins.
Damselflies hold the wings vertically over the body or partly spread when at rest, whereas the dragonflies always rest with
wings outspread. Abdomen with a pair of small, 1-segmented cerci. Simple metamorphosis, with 10-15 nymphal instars depending
on species. The nymphs are aquatic, living in freshwater ponds, lakes, rivers and streams. They breath by means of internal
rectal gills (dragonflies) or by means of three external abdominal 'tails', which form feather-like caudal gills (damselflies).
The mouthparts of nymphs are cleverly modified to form an elongate, prehensile structure known as the mask. This
structure is hinged in the middle and bears a pair of terminal claws. The whole arrangement is called the mask because
when not in use and folded back under the head, it conceals the rest of the mouthparts. When food is sighted, the mask is
thrown forward and the prey is impaled on the claws. Over 4,500 species are described worldwide and just over 40 of these
are recorded from the British Isles.