What are Dragonflies and Damselflies?
Dragonflies and damselflies belong to the group (or Order) of insects known as Odonata, a primitive and successful group whose ancestors appear in fossil records some 300 million years old and is largely unchanged today – many of today’s recognisable Odonata families emerged 200 million years ago; Odonata came before and outlived the dinosaurs. They live in a broad range of environments and can be found on every continent except Antarctica.
Like all insects, they are invertebrates with a body divided in three distinct sections: the head, thorax, and abdomen. They have three pairs of segmented legs, a pair of large compound eyes and a pair of small antennae.
Today there are about 7,000 species of Odonata, divided into two distinct groups or sub-orders: Anisoptera (the true dragonflies) and Zygoptera (the damselflies). There are slightly more dragonfly species than damselflies.
In the UK, the term ‘dragonflies’ is often applied to all Odonata, including damselflies. This makes the distinction between true (Anisopteran) dragonflies and damselflies difficult at times! Some suggest calling Anisopteran dragonflies ‘Warrior flies’, but in the UK at least this hasn’t gained much ground. To help avoid this confusion we generally refer to Anisopteran dragonflies as dragonflies, Zygoptera as damselflies, and the whole order collectively as Odonata.
Odonata have distinctive features
- A life cycle with three distinct stages: the egg, the life as an aquatic larva or nymph, and the final phase after leaving the water to become flying insects.
- A unique method of reproduction.
- They are carnivores and fierce predators of other insects, including other Odonata.
- The abdomen is long and divided into ten segments.
- Two pairs of large wings that can move independently of each other.
- A pair of large compound (multi lensed, comprising thousands of individual Ommatidia) eyes that give almost 360° stereo vision, and three more eyes made of a single lens each.
- A pair of small, inconspicuous antennae.
Odonata, and dragonflies in particular, are superlative fliers and able to fly seemingly indefinitely (they do land though!), they can hover, fly forward, backwards and sideways and change direction endlessly as they chase prey at great speed or seek a mate.
Differences between dragonflies and damselflies
Dragonflies and damselflies are closely related, but what separates them?
- Generally, dragonflies are powerful fliers and tend to be larger and more robust than damselflies. Damselflies in contrast have a weaker, fluttering flight, and much more delicate bodies.
- The eyes of dragonflies are very large, and in most species meet at the top of the head. Damselflies have smaller eyes that are separated on either side of the head.
- Dragonflies have dissimilar sized pairs of wings, the rear wings being broader – Anisoptera means ‘unequal wings’.
- Damselflies have similarly sized pairs of wings – Zygoptera means ‘equal wings’.
- Though not an infallible rule, dragonflies tend to rest with their wings held open and damselflies with their wings closed.
Why are dragonflies and damselflies important?
Humans don’t exploit Odonata commercially on any large scale, but in some cultures, they are used for medicinal purposes, and they can be a snack or a delicacy at the dinner table. But although there is little exploitation, they are especially useful as ecological indicators.
Dragonfly and damselfly larvae require clean, unpolluted, waters to thrive, and it follows that their presence is a good indicator of water quality. As adult airborne insects they require that the surrounding environment is free from pesticides, and that it supports a variety of flora and fauna which in turn supports the insect life that Odonata feed upon.
With increasing awareness then, we realise Odonata are sensitive indicators of environmental quality and play a key role in demonstrating that habitats are responsibly managed and are sustainable. This is a primary conservation aim and is of benefit to us all.
Risks to Odonata
While dragonflies can be abundant in some environments, they are susceptible to the human impact of pollution, habitat mismanagement and environmental catastrophe.
This is especially true when they have specialised habitat requirements; following accidental pollution of their only breeding site during the 1960s, the Norfolk Damselfly became extinct in the UK. In Bedfordshire the Scarce Blue-tailed Damselfly was not seen for 20 years following the demise of its only habitat at Sundon Chalk Quarry, however it has recently been seen again at the site
Of the thousands of species worldwide less than 50 are common to the British Isles and almost 30 of these occur in Bedfordshire.
Climate change is likely to affect Odonata distribution and over the last 20 years more species are visiting and establishing breeding colonies, both in the UK and Bedfordshire. We also attract migrants and vagrants from time to time, and new species may turn up. Whether these movements are long term range expansions or not remains to be seen, but the world of dragonflies and damselflies is constantly changing.