These are commonly known as the narrow-winged damselflies, and there are 13 British species. Their adult body length ranges from 25 - 50 mm, and they contain the largest number of species in Northern Europe. The adults are usually red and black or blue and black.
On the left is Coenagrion pluella, the Azure damselfly or Pond damselfly. Its wingspan is 41 mm and body length 33 mm. The adult flies from May to August. It is found near water meadows with lush grass, canals with abundant reeds, ditches and is one of the most common found in garden ponds. It is common in England and Ireland, but less common in Scotland. This one was just moulting into and adult. The female lays her eggs in the tissues of plants on the water surface.
The venation of the wings is used in identification to species level, however there is disagreement between entomologists in naming the veins, so identification for a beginner is usually easiest using illustrations.
They have 10 or 11 abdominal segments. All males have a pair of claspers on segment 10, and their reproductive organs on segment 2 or 3. In females the ovipositor is in segment 8 or 9. Some females may have a pair of appendages on segment 10.
Before mating the male must transfer sperm from the genital opening on segment 9 to the reproductive organs on segments and 3. Then on finding a female he grabs her by the neck with his claspers. She curves her body around until the tip of her abdomen touches his reproductive organs in segment 2 and 3 to collect the sperm. This is known as the copulation wheel. After mating the pair may fly in tandem with the male leading. Females mate with more than one male and store the sperm from the matings, although she tends to use the sperm from the last mating. The male mating organ contains a structure that allows him to scrape or push aside the sperm from previous matings before depositing his own in the most favourable spot. The length of time he holds on to the female (the copulation wheel) will also prevent her mating with another.
The female places her eggs in the water, usually on the stems of aquatic plants. Some species actually crawl underwater to place their eggs deeper, some have a saw-like structure on the ovipositor to make slits in plants enabling them to place the egg inside the stem, and others just skim over the water dipping the tip of their abdomen in and scattering the eggs singly. In some species the male holds on to the female while she lays eggs. Adult life span can be as long as 2 months, but is usually no more than 2 or 3 weeks.