The dragonflies and damselflies that adorn a variety of watery areas throughout the summer months belong to the order of insects known as Odonata, a term that literally means 'straight winged'. Typical features of this group of insects are a large head and compound eyes, long prey catching legs, two pairs of independently moving wings that are transparent, elongated abdomens and short antennae. The wings contain a colored cell found along the leading edge known as a pterostigma, this is used to help in flight, particular gliding movements. Odonates are aquatic or semi-aquatic as juveniles and they go through an incomplete metamorphosis.
The are several difference between dragonflies and damselflies, the main ones being:-
Dragonflies - Large, bulky with more powerful, direct flight. The forewings are narrower than the hind wings with both pairs held open when resting. The eyes are prominent and wrap around the front, top and sides of the globular head.
Damselflies - Small, slender with weak, fluttering flight. Wings are similar in size and when at rest are held vertically closed along the top of the abdomen. The head is rectangular with eyes at the outer ends.
To add to the above - Dragonflies are insects in the sub-order Anisoptera meaning 'unequal-winged'. Damselflies are insects in the sub-order Zygoptera meaning 'paired-wings'.
There are 39 breeding species of Odanata in the UK with several regular migrants and a few irregular visitors that may occasionally breed.