We know they are Damselflies because they almost all rest their wings together, above their bodies, whereas dragonflies rest with their wings spread diametrically apart. Beyond that though, Damselflies can be tricky things to identify with marked differences between the sexes and between mature and immature, and also with different colour forms in some cases.
But we’re almost certain they were a pair of Common Blue Damselflies (Enallagma cyathigerum) because of the colours and patterns and because the second segment of the thorax has a distinctive spot with a line below connecting to the third segment. Based on the photos on the British Dragonfly Society’s website our top picture is of the male and the much paler female is below. They were lounging around in the picnic clearing on a sunny late May a long way from water but Naturespot says that although they favour open water habitats adults can (unlike most of their relatives) be found away from water ‘in shady spots such as woodland rides’.
Wikipedia adds that during mating, the male clasps the female by her neck while she bends her body around to his reproductive organs – this is called a mating wheel. No wonder they needed a rest. The pair then flies together over the water and eggs are laid within a suitable plant, just below the surface.
Damselflies are similar in most respects to their close relatives, the dragonflies. The eggs hatch and the larvae, called nymphs, live in the water and feed on small aquatic animals. Nymphs climb out of the water up a suitable stem to moult into damselflies. The adults then catch and eat flies, mosquitoes, and other small insects. Often they hover among grasses and low vegetation, picking prey off stems and leaves with their spiny legs.