Odonata (dragonflies and damselflies)

Damselfly nymph

Damselfly nymphs

The nymphs (see the damselfly nymphs left and below) are aquatic, carnivorous and sluggish. They are slender, with 3 leaf-shaped tails, and are much better swimmers than the fatter dragonfly nymphs.

On hatching from the eggs the larvae start feeding at once. They have a prehensile lower lip (called the mask) which is folded under the head at rest (see the drawing of Agrion puella below). This has moveable teeth, and the whole thing can shoot out at great speed to grab prey. They tend to creep around the bottom of ponds and streams searching for prey. Dawn or dusk during fine weather are the most common times for moulting. There are usually 10 - 15 moults as nymphs. It can take nymphs from 1 to 5 years to mature depending on species. When a nymph is about to moult into an adult it crawls out of the water.

Lestidae family, Emerald damselflies

There are just 2 British species in this family. The adults are metallic green, and the nymphs prefer still waters. Above left is a damselfly nymph, possibly Lestes sp. Note the leaf-like tail filaments and slimmer body. This one came as an egg in the stem of some plants I ordered for my pond. With the popularity of garden ponds increasing this may be a new method of dispersal.

Adult Lestes sp. fly from June until the first frosts.

On the right is an Agrion puella nymph, with a more detailed drawing of the mask. All nymphs are carnivorous, and the larger ones will even catch tadpoles and small fish.

Damselfly adults are smaller and more delicate than dragonflies, and they have weaker flight. Though their flight is weaker than dragonflies they are pretty strong fliers and eat other insects, especially mosquitoes, black flies and other small flies, that they catch on the wing. They have a row of stiff bristles on either side of their legs, so the three pairs form a basket to scoop flying prey. However because of the positioning of the front legs Odonata cannot walk or crawl. Damselfly flight speed has been recorded as 1.5 metres per second and 16 wing beats per second. Compare this with other insects.

Females and males of the same species are often different colours, and younger adults are usually a paler colour than older ones. The beautiful colours of the adults fade after death.

Agrion puella damsel fly nymph
Coenagrion pluella, damselfly adult

Coenagrionidae family

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.

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