To hunt other flying insects, dragonflies rely on their excellent vision and superb flight skills. Their other senses are poor. Dragonflies, and many other kinds of insects, have no sense of hearing. The antennae of many insects are large and packed with chemical receptors giving them superb senses of smell, taste and touch, but a dragonfly’s antennae are small and their main function is to measure air speed in flight.

The word "dragon" comes from an ancient Greek word meaning "sharp-sighted one".

The compound eyes of a dragonfly are huge compared with the size of its head. (If you were a dragonfly, your eyes would be the size of a football helmet!) Each eye is made up of 30,000 telescope-shaped ommatidia (singular = ommatidium). Each one collects light from the direction it points, and the brain processes this to make a nearly 360 degree field of view. Compound eyes cannot change focus, like human eyes, so only objects that are close to the dragonfly appear in clear detail. A dragonfly doesn’t see as much detail as a human can, but its eyes and brain are extremely sensitive to motion. They can detect movements separated by 1/300th of a second! To a dragonfly, a movie might look like a series of still pictures.

Dragonflies have binocular vision, so they can judge distances. They have colour vision, but see from orange to ultraviolet (UV) light. Insects don’t see red light, while we humans can’t see UV light. An object that reflects UV can appear quite different to an insect than it would to our eyes. Dragonflies also sense light polarization. Sunlight scattering in the atmosphere or reflecting off water becomes polarized. That means, instead of being randomly aligned, the light waves tend to line up. This creates patterns in the sky that show directions, and makes water surfaces highly visible.

A dragonfly's ocelli, or simple eyes, are very sensitive to light intensity. They may be involved in determining night from day, and regulating circadian rhythms.

Dragonflies may be the best fliers on Earth. They can fly forward, backward and turn almost instantly. They can hover, turn while hovering and accelerate to full speed in a split second, then glide effortlessly. Mated pairs can even fly together in tandem. Imagine tethering two helicopters together and trying to fly them!

Dragonflies are among the swiftest flying insects, proven to reach air speeds of 38 Km/h.

Each of a dragonfly’s wings operates independently, providing great maneuverability. They are powered by direct muscle action, the flight muscles are anchored directly to the ends of the wings. Most flying insects, like butterflies, flies and bees, have indirect flight muscles, which change the shape of the thorax to power the wings. Dragonfly wings beat about 30 times/second, which is slow compared to some insects with indirect flight muscles. Mosquito wings beat 300 times/s.

In "direct flight" the muscles that raise (green) and lower (red) the wings are both attached to the end of the wing and the bottom of the thorax.

In "indirect flight" the muscles that raise (green) the wing are attached to the top and bottom of the thorax, while those that lower (red, in cross section) the wings are attached at the front and back of the thorax.

Active flight uses a lot of energy. A flying dragonfly uses 100 times more energy than one at rest. Some dragonflies must eat about 20% of their body weight a day just to power their flight. A “fully fueled” dragonfly can only fly for 8 hr before exhausting its reserves of fat.

The wing actions, in slow motion,
of a dragonfly hovering. (Rear wings in blue.)

 

A "shivering" dragonfly.
(Video = 30 sec., 0.9 Mb)

Dragonflies must be warm to fly. Temperature in the thorax must be over 25 C. Most species are active during the day and bask in the sun to warm up. Some large dragonflies generate heat by shivering their flight muscles before takeoff. This allows them to fly early in the morning or at dusk.

 

Watch a higher resolution version of this video on YouTube. Click Here: Shivering!

 

On hot, sunny days a dragonfly can get too warm. Active flight generates a lot of heat. To cool itself it can stop flying and roost in the shade. If no shade is available it will sit with its abdomen pointing at the sun (called the "obelisk position") to reduce solar heating. Some dragonflies will even dip their bodies into water as they fly to promote evaporative cooling.

When not hunting, at night and during bad weather, dragonflies perch under leaves or other shelter.


1) Basic Biology

2) Life Cycle

3) Palaeobiology

4) Biodiversity

5) Biogeography

6) Overwintering / Migration

7) Food

8) Sight and Flight

9) Cultural Significance

10) Conservation

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