Odonata enjoy two very different stages in their life cycle; aquatic larvae and aerial insects.
The cycle begins when fertilised eggs are laid by adult dragonflies or damselflies. Depending on the species, eggs are laid either in water where they fall to the bottom, or injected into mud, rotting wood or vegetation, or emergent bankside plant and reed stems. Usually the eggs hatch after a few weeks, but in some species they will hatch the following spring.
The resultant larvae live underwater from a few months to a few years dependant on species and climate – colder climates having a longer development, before emerging from the water to begin their adult life as aerial insects to begin the cycle once again.
To enable them to live underwater, just as with fish both dragonfly and damselfly larvae extract oxygen from the water using gills. The gills are internal in dragonflies but in damselflies they form 3 fan-like structures situated at the end of the abdomen, called Caudal Lamellae. Damselflies use their caudal lamellae as respiratory organs and also for swimming. To extract oxygen, dragonfly larvae are able to force water over their internal gills using muscle contractions. Damselflies however must either fan their gills or move through the water to ensure adequate supply of oxygenated water.
In common with other insects, the skin (cuticle) of Odonata is inelastic and doesn’t grow. So that a dragonfly or damselfly larva may increase it’s size, it must periodically shed it’s skin. This process is called Ecdysis and each successive moult marks the start of a new Stadium. There may be 8-15 stadia depending on species
During this time the larva is vulnerable to other predators as the larva must remain inactive as the cuticle hardens.
The final moult marks the end of the aquatic stage for the larva and must take place outside of water. The larva leaves the water by climbing an emergent plant stem or reed, and completes its miraculous transformation, finally shedding its larval skin a final time exposing its wings. The body expands and wings inflate by the pumping of body fluid around the network of veins. This process may take an hour or more.
Finding the shed larval skins (Exuvia) after emergence is useful and definitive proof of successful breeding at a site.
After a short rest while the wings and body hardens, the newly emerged dragonfly or damselfly is able to fly, but still isn’t fully matured and will generally fly away from water to find food and avoid other mature Odonata. During this time Odonata can often be found some distance away from water, and they are less territorial, busying themselves with feeding rather than finding a mate.
Once matured, which usually takes 3-7 days, adult Odonata return to water to breed, and start the cycle once again for another generation.
Adult dragonflies and damselflies have a shorter life than larvae, and usually only live a few days or weeks. Unlike larvae, they don’t grow or need to shed their skin – dragonflies and damselflies are the finished article.