Dragonflies
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.
When flying or resting amongst the vegetation, dragonflies are recognised for their bright iridescent and metallic colours that flash in the light. 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.
Female dragonflies such as the Brown Hawker (Aeshna grandis) lay eggs in dead wood or debris using their sharp ovipositors. Source: Shropshire Dragonflies, 2023.
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 dragonfly life cycle comprises three main stages: Egg, Nymph and Adult Stage. Source: Carlos, 2022.
The life cycle of dragonflies compose 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.
References
Barnard, P.C. 2011. The Royal Entomological Society Book of British Insects, John Wiley & Sons, Incorporated, Hoboken. Available from: ProQuest Ebook Central. [Accessed: 10 January 2023].
Biodiversity Ireland, 2021. Irish Dragonflies and Damselflies – National Biodiversity Action Centre. Available at: https://biodiversityireland.ie/irish-dragonflies-damselflies/#:~:text=30%20Dragonfly%20and%20Damselfly%20species,species%20and%205%20vagrant%20species. [Accessed: 18/01/2023]
Bomphrey, R.J., Nakata, T., Henningsson, P. and Lin, H.T., 2016. Flight of the dragonflies and damselflies. Philosophical Transactions of the Royal Society B: Biological Sciences, 371(1704), p.20150389.
Carlos, 2022. Grasshopper Life Cycle – 3 Stages & Unique Characteristics – Learn About Nature. Learn About Nature. Available at: https://www.learnaboutnature.com/insects/grasshopper/grasshopper-life-cycle/. [Accessed 18/01/2023]
Piercy, K., 2021. When and How Do Dragonflies Mate? (Questions Answered). meadowia.com. Available at: https://meadowia.com/when-and-how-do-dragonflies/. [Accessed: 17/01/2023]
Shropshire Dragonflies, 2023. Life Cycle. Available at: http://shropshiredragonflies.co.uk/egg/. [Accessed: 15/01/2023]
Smallshire, D. and Swash, A., 2014a. Life Cycle and Biology – British Dragonfly Society. British Dragonfly Society. Available at: .https://british-dragonflies.org.uk/odonata/life-cycle-and-biology/. [Accessed: 17/01/2023]
Smallshire, D. and Swash, A., 2014b. Life Cycle and Biology – British Dragonfly Society. British Dragonfly Society. Available at: https://british-dragonflies.org.uk/odonata/dragonflies-2/. [Accessed: 17/01/2023]
Ware, J.L., 2021. Odonata. Current Biology, 31(2), pp.R58-R59.
Written by Amanda O’Driscoll
