The word “Dragonfly” is a wide term used for insects in the order Odonata, which encompasses both the Damselflies and Dragonflies. True Dragonflies have their own distinct suborder Anisoptera (meaning “unequal wings”). Odonates are considered an ancient insect group; fossil records date back to the Triassic period approx. 252 million years ago! The distribution of Dragonflies worldwide is far reaching – they’re found on every continent with the exception of Antarctica. There are approximately nine families in the suborder Anisoptera, with 3,100 species recognised internationally. The region with highest biodiversity for this group is in the Tropics due to its warm climate. In Ireland, there are 14 native species in our wetland habitats, with five additional vagrant species that migrate during the seasons.
There are 30 species of Odonata in Ireland; 14 of which are true “Dragonflies” from the Anisoptera suborder. Five of the total Odonata species are vagrants, i.e.they are migrants that travel to different countries during the seasons.
When flying or resting amongst the vegetation, dragonflies are recognised for their bright iridescent and metallic colours that flash in the light. Dragonflies are distinguished by their thick abdomens, large compound eyes that give them acute vision and long wings on the back of their thorax for efficient flying. Their iridescent bright green and blue colours allow them to camouflage easily in the environment.
Another characteristic feature which distinguishes Odonates is their reproductive stage. Males get the attention of the female by a “dancing” display of its wings and exerting its territory. If this is successful, the male attaches itself to the female’s thorax with its legs and holds its abdomen to the back of the female’s head. Next the female brings her abdomen under her body in a circle to receive the sperm from the male’s secondary reproductive organ (called the vesica spermalis) found on the tip of his abdomen. This position is known as the “Copulatory Wheel” and is the first stage in the reproductive process. During this stage the male might remove any sperm in the female’s abdomen belonging to other males using a sharp scraper on the tip of his abdomen. Once this is complete and the sperm is transferred to the female, the couple then fly in a straight line while still attached, known as the “tandem position”.
The female then begins egg laying. There are two ways in which females lay their eggs: Endophytic laying where the female uses sharp, piercing ovipositors to deposit eggs within the leaf tissue or rotting wood and; Exophytic laying where the female’s abdomen tip is repeatedly submerged in water, depositing the eggs within a jelly like substance for protection and to retain moisture.
Hatching times vary for many species of dragonfly; they can either be within 2-5 weeks or for some dragonflies such as the Emerald Dragonfly, Chasers, Skimmers and Darters it can be next spring before young nymphs emerge.
The life cycle of dragonflies composes of the egg, nymph and adult stages. Dragonflies undergo a process called hemimetabolous, in which they do not have a pupa stage but undergo development through various nymph stages before arriving at adulthood. As a result, the nymph stage is the longest development stage, lasting usually two years during which a dragonfly will moult up to 14 times, before reaching adult form. Dragonfly nymphs have inconspicuous coloration of brown, green and black to camouflage from aquatic predators.
Dragonflies often act as bioindicators of the surrounding freshwater environment. Changes to water conditions such as pH levels (too acidic or basic) and heavy nutrient loading (termed eutrophication) of carbon and phosphorus can negatively impact their survival. As a result, dragonfly species abundance in wetland habitats is a useful tool for scientists to monitor the health status of freshwater habitats.
Dragonflies are voracious predators and feed on small aquatic larvae or invertebrates during their nymph stage. As adults they use their forward positioned legs to capture prey on the wing. In fact, they are fast and agile fliers, capable of racing speeds of 36 km/hr. By preying on smaller insects, dragonflies maintain population numbers and reduce rapid growth of small insects by feeding on them. This in turn prevents swarms of insects infesting the land and provides food for other animals in the food web.
Next time you find yourself by a freshwater system keep an eye out for an iridescent flash of colour and appreciate the beauty of the dragonfly.
