Dragonflies: Chasers, Hawkers and Darters
The dragonfly is a most beautiful insect and one which causes delight when seen on a bright summer's day. It is a pleasure to see the sunlight catch the dragonfly's delicate, graceful wings and colorful body.
Dragonflies fall into two categories - hawkers and darters depending on their style of hunting. All dragonflies are predators and eat other insects as their prey.
The hawker dragonflies known as Aeshnidae in Latin, fly in a long, sustained manner around the waterways, ditches, ponds and riverbanks where they like to hunt. Darter dragonflies are known as Libellulidae in Latin hunt differently. Perched expectantly upon a reed or leaf they dash speedily out from cover to capture passing prey.
The hairy dragonfly, Brachytron pratense is a hawker dragonfly of the Aeshnidae family. The four-spotted chaser dragonfly Libellula quadrimaculata (known as four-spotted skimmer in the USA) is one of the Libellula family of dragonflies.
Dragonflies have close relatives known as damselflies. They belong to the insect order known as the Odonata. Dragonflies are called Anisoptera in Latin and damselflies are known as Zygoptera in Latin.
Just like the difference between butterflies and moths, the difference between dragonflies and damselflies is how they hold their wings when resting. Dragonflies and moths hold their wings horizontally and flat at rest but damselflies and butterflies hold their wings together and closed upon their backs. Dragonflies are also larger than damselflies.
Four Spotted Chaser Watercolour Artwork by Alison Langridge
Both dragonfly and damselfly larvae live underwater and undergo complete metamorphosis. This means that the young look different from the adult dragonflies. Another name for this is 'endopterygota' metamorphosis. Damselflies are more slender in shape than dragonflies.
Dragonfly and damselfly wings consist of transparent membranes supported by a fine and delicate network of veins. This adds to the dragonfly's beauty and charm. Coloured patches on their wings are 'pterostigma'. Some dragonflies that have names such as four-spotted chaser, for example, is on account of them having four pterostigmata on their wings.
Broad-bodied Chaser Dragonfly Watercolour Artwork by Alison Langridge
Direct muscle motion is when dragonflies and damselflies beat their wings up and down from their thorax. Flies and other insects use indirect muscle motions which is more complex. Bumble bees for example beat their wings in a figure of 8 motion. As the dragonfly flies, they use their legs to form a basket or net to capture its prey.
Although dragonfly wings look so delicate it is amazing to think that dragonflies once had a wingspan of 70 cm or 27 inches in the past. Fossils of extinct dragonflies show that they were once huge in size. It's hard to imagine such large insects in flight. Perhaps fossil evidence may one day reveal what these ancient dragonflies ate.
Dragonflies and damselflies have the most sophisticated eyesight of any insect. This is in spite of them being called primitive insects. They hunt at speed, like a bird of prey, following a moving target. Insect eyes gather an immense amount of visual information when in motion. This is in addition to computing speed, distance, direction relative to their surroundings.
Like most other insects, dragonflies and damselflies have compound eyes. A compound eye is made up of tens of thousands of separate units called ommatidia. Ommatidia are like minute telescopes. Each eye may have 20 thousand ommidatia radiating outward from the eye centre forming a highly focused bundle. This radial arrangement of ommatidia covers an extensive visual range.
Dragonflies focus on their prey when they are great distances away. It is hard to think of a human equivalent and if it was possible to imagine how a dragonfly sees and hunts on the wing it must be remembered that it does so in the air and not in one plane on the ground. The brain of a dragonfly must be far most sophisticated than its size to process such a large amount of visual information.
Odonata antennae are not as sophisticated as a bee or wasp for example that live in colonies and use taste, smell, touch, and vibration.
There may be around 25 species of dragonflies and 21 species of damselflies in the UK. Scarlet dragonfly, banded darter, lesser emperor, green darner, small red-eyed damselfly, southern emperor damselfly, and common winter damselfly have recently been discovered in the UK. Worldwide there are around 6,000 species of Odonata.
Dragonfly and damselfly larvae are called nymphs. Nymphs also hunt and predate upon other water insects and even small fish which make them unwelcome guests in freshwater fish hatcheries.
Odonata larvae can spend up to five years in the larval stage before undergoing metamorphosis and become beautiful flying adults. Larvae mouthparts act as pincer-like claws that can extend from its head to seize its prey. Dragonfly larvae breathe through gills in its rectum. These rectum gills enable them to shoot forward or away by jet propulsion rather like the way cuttlefish and squid move.