Dragonfly & Damselfly Biology

Dragonflies and damselflies (collectively termed the odonata) are among the most attractive of insects, with iridescent colouring and dazzling displays of aerial acrobatics.

Dragonflies and damslflies are in essence aquatic insects, spending most of their lives as larval stages in freshwater habitats. Both as nymphs and as adults, they are voracious predators. Despite this they are harmless to humans and as adults can be safely held in the hand.

Life cycle

The life cycle of dragonflies and damselflies consist of three distinct stages:

Eggs

The eggs are tiny (<0.75mm) and are either laid singly on the inside of the stems or leaves of aquatic plants, or in clusters into water or wet mud. In suitable temperatures the eggs can hatch in 2-5 weeks. However, eggs laid in autumn may enter a period of suspended development due to low temperatures and will only hatch the following Spring.

Larvae

Once hatched, the larvae moult through between 6 and 18 larval instars. Dragonfly larvae are larger and more robust than damselfly larvae. As in the adults, the eyes of damselfly larvae are set far apart.

Larval development typically lasts one or two years but can take just a few months in some damselfly species, up to 5 years for the Golden-ringed dragonfly. Larvae feed on freshwater macro-invertebrates and even small fish.

Adults

Newly emerged adult dragonflies and damselflies are termed ‘tenerals’. Tenerals are very delicate (and should not be handled), show little body colouration, and have a distinct sheen to the wing membranes. The teneral stage lasts about a day but in some species it can take up to two weeks for adults to achieve their mature colours.

Newly emerged adults seek out areas away from the water in which to feed and roost. Damselflies are the most likely to congregate in sheltered areas close to the breeding site. Dragonflies are likely to disperse more widely and hunt as single individuals in sheltered woodland.

When adults reach sexual maturity they return to water to mate and lay. Males tend to monopolise the areas around the breeding pools, with dragonfly males typically exhibiting territorial behaviour. The adults feed on smaller insects but may also take smaller dragonflies and damselflies, butterflies and bees.

In poor weather and low temperatures, dragonflies and damselflies cannot fly and will rest in a variety of vegetation. Dragonflies and damselflies are predated upon by birds, spiders, frogs and newts. They may also be consumed by carnivorous plants.

The duration of the flight period for most Irish species is 15 – 22 weeks, but most individuals die within a few days of emerging due to weather and predation.

 

Blue-tailed damesfly (Ischnura elegans) – Will Woodrow

Value as Bio-indicators

Dragonflies and Damselflies can be used as bio-indicators of water quality and freshwater habitat quality. They typically spend 1 to 2 years of their lives as aquatic nymphs, require good water quality to survive to adulthood, and can react quickly to changes in environmental quality.

Dragonfly and damselfly nymphs are commonly used as bio-indicators of water quality, using kick-sampling techniques. However in-water sampling is not desirable from a citizen science perspective.

Luckily, adult dragonflies and damselflies are readily available for visual survey without getting your feet wet! They are also reasonably easy to identify to species level. With a bit of caution, adult dragonflies and damselflies can also be used to assess water quality and freshwater habitat quality.

Some species, such as the Emperor Dragonfly, can also be used as bio-indicators of climate change as they expand their range to the north in response to increasing average temperatures.

Surveying Dragonflies & Damselflies

Weather

Surveys should be carried out on dry, sunny, cloudless, and windless days. Ideally the temperature should be above 17oC, though for Irish conditions, 15oC is the recommended minimum . Often surveys during the first sunny weather after a prolonged period of poor weather can be most productive. As it takes a while for dragonflies and damselflies to warm up and get active, it is generally recommended to survey between 10AM and 4PM.

Visual Survey

Dragonflies and damselflies may be observed without the aid of any equipment. Just wait until the animal perches on some low vegetation and approach slowly and carefully. This task is often easier in dull, cooler weather. To observe more distant animals or those on the wing over water, a pair of close-focusing binoculars may be used.

Netting

For those with more than a passing interest in dragonflies and damselflies, a net is a worthwhile investment. An insect net made of black lightweight nylon is best. Nets with a telescopic aluminium handle may prove useful. Ensure that your net has sufficient depth to allow the net to close over the entrance by flipping the handle.

Never attempt to net newly emerged adults (tenerals) as they are too delicate. Tenerals may be recognised by their shiny wings and lack of colour. Never use a wet net as it may damage the insects.

Damselflies may be netted by sweeping when the animals are perched or in flight. Dragonflies are best netted by sweeping up and from behind the animal.

Handling

Grasp the insect at the base of the wings, gently closing them between finger and thumb. This will not hurt them an you can release by placing on a suitable perch and letting go.

Photography

The best times to photograph dragonflies and damselflies are early morning and late afternoon when temperatures are below those required for flight. Chasing after highly active animals during the hotter parts of the day generally does not yield good results, though some success may be had with a good zoom lens. Days of mixed cloud and sun can be productive as animals settle while the clouds pass over, don’t forget to leave them settle for a few minutes before trying to approach to take a photo. Searching low lying branches and shrubs near to breeding pools can also yield results.

Estimating Numbers

Where numbers of animals are low, direct counts for each species may be attempted. Where numbers are higher, estimating according to count codes may be more realistic e.g. A=1, B=2-5, C=6-20 etc… In mixed species groups or damselfly or dragonfly, the total count for each species may be extrapolated by catching and identifying a representative sample (e.g. 10%) of the animals.

 

Dragonfly anatomy

Damselfly anatomy

Identifying Dragonflies & Damselflies

Boys & Girls

Males and females of dragonfly and damselfly species may differ markedly. Generally, it is best to focus on males initially for identification purposes as they are more colourful and more clearly marked. When surveying, males are more likely to be found closer to the water and therefore it is recommended to focus your search within 2m of the water’s edge (where it is safe to do so), and 5m over the surface of the water (visually).

Females tend to have more drab colours and are more easily confused with other species. The further you are from the water’s edge, the more less likely you will find males and more likely you will find females.

 

Exuviae & Tenerals

Exuviae are the larval casings left behind by newly emerged adult dragonflies and damselflies. The exuviae retain the larval form and can be identified to species. They are generally found on vegetation at the water’s edge but can be difficult to locate. Exuviae are best stored wet in 70% alcohol for identification purposes.

Tenerals are the recently emerged adults. They tend to have shiny wings and are lacking the colour of the mature adults. Tenerals are also far more delicate than the mature adults and should never be handled or netted.