Dorset’s four-winged predators
Jenny Elliott looks at the county's damselflies and dragonflies
Published in March ’13
Dragonflies are split into two groups, dragonflies and damselflies. They have inhabited the earth for millions of years. One prehistoric fossil has a wingspan of two and a half feet. True dragonflies are large powerful fliers with two sets of transparent wings. They are very versatile aviators and can hover, loop the loop and even fly backwards. They are unable to fold their wings and when flying or at rest their wings are held at right angles to their bodies. Odonata is the scientific name for dragonflies and means toothed jaw. Much of their time is spent hunting for prey and they have excellent eyesight for this purpose. Their eyes have about 30,000 individual lenses and can detect the slightest movement. Up to six hundred insects a day can be consumed by one dragonfly so they are able to help enormously in keeping mosquito numbers down. At one time the native Burmese regularly released dragonfly nymphs into the water that surrounded their settlements to control the mosquitoes that carried Yellow Fever. They are viewed as pests by most beekeepers as they can have a devastating effect on a bee colony. Dragonflies are able to eat on the wing but will sometimes land to devour their meal. They have barbed legs, which are very effective at catching insects in mid-air, but are absolutely no good for walking. In fact, they are unable to walk at all. Dragonflies only take to the air when the weather is warm. The muscles in their wings won’t function unless warmed by the sun.
Dragonfly nymphs are ferocious predators and will eat mosquito larvae, lesser boatman, pond snail eggs, water fleas, small fish and even other dragonfly nymphs. They live in the water for up to six years. As you can see, the greater part of their life is spent underwater. The nymphs have a special gill chamber which extracts oxygen from the water they have taken in. This means they don’t have to surface to breathe. This ingested water can also be used to jet propel them away from danger when they feel threatened. When this stage is complete the nymph will crawl out of the water and up a stem of a plant where it sheds its skin. It then pumps its wings with blood to make them stiff, the sun will dry its body and wings and it is ready to take its first flight. If maturity is reached during the winter they will hibernate until the spring and the warm weather before leaving the water. The life cycle then begins again. Dragonflies often mate in the air. After mating the female will lay her eggs, up to one hundred a day. They are usually laid on plants growing on the margins of ponds.
Damselflies are generally smaller and have a weaker flight. They tend to stay close to vegetation and water and don’t fly the long distances that dragonflies do. They, too, are very adept at catching insects on the wing.
Unlike the dragonflies they are able to fold their wings against their bodies when at rest. Their eyes are not as large and are separate – unlike the eyes of a true dragonfly, which meet. Their lifecycle is between one and two years. Damselflies usually mate whilst attached to vegetation on the waters edge. After mating the female will descend into the water to lay her eggs. Once the eggs have been laid she will crawl back up the stem to mate again.
We are very fortunate in Dorset to be able to see these insects in abundance on our ponds and rivers.