Genevieve Dalley, Trainee Ecologist with RSPB Scotland, is back with a new blog.
The Ugly Duckling
It’s a familiar story: the unassuming youngster undergoes a magical transformation to become a beautiful adult. The most quoted examples from the insect world are butterflies.
However, there are other creatures out there who, after sometimes years of life trapped in their larval skin, burst forth and take flight. The freshwater creatures which do this are possibly the most remarkable examples of such a lifestyle- adapted to life in water when young and life in the sky as adults. Here is a brief introduction to some of these unfamiliar wonders...
Dragonflies & Damselflies
The dragonflies and damselflies are probably the best known freshwater insects which make the incredible transition from water to air. Whilst familiar in the sky, few people are acquainted with the larval forms of these animals. Yet they can be just as beautiful.
Emerald damselfly nymph (Lestes sponsa).
As they grow, the nymphs periodically shed their skins and pump their bodies up as fast as possible before the new one hardens.
Common darters (Sympetrum striolatum): the pale one has recently shed its old skin and is waiting for the new one to harden.
When the time comes, which can take up to 5 years, the nymphs suddenly get the urge to find a suitable spot to emerge. They can travel impressive distances, sometimes crawling over land, in search of the right spot. Then they break through their old skin and heave themselves out, occasionally pausing for rest, before fully emerging. Finally, they must to pump their wings with fluid, warm up and, after years of waiting, take flight!
A blue-tailed damselfly (Ischnura elegans) pausing halfway out of the larval skin.
A golden ringed dragonfly (Cordulegaster boltonii) resting beside his old larval skin (exuvia).
The mayflies are best known for their infamously short life. However, their flying forms are just a small part of the story. To get to that stage they must first live an underwater life. At this stage they can look remarkably unrecognisable.
A mayfly nymph Electrogena lateralis
After up to two years as a nymph, the time comes to emerge into adult life. The mayfly nymph swims to the water surface and breaks free of the old skin. The newly emerged mayfly rests on the water surface waiting for the wings to dry. At this stage, many mayflies are eaten by fish or birds, never developing into full adults.
This first winged stage is known as the sub-imago, a mayfly's teenage years. After a few hours the sub-imago once again sheds its skin and the colourful adult fly emerges.
Part of the lifecycle of a Mayfly: A mayfly sub-imago (Siphlonuridae), a sub-imago exuvia (Ephemeridae), an adult mayfly (Siphlonuridae).
These creatures go largely unnoticed as nymphs and adults but they are no less interesting. A few days before emergence, the nymphs stop eating and make the final changes to their internal bodies needed to start on their adult life.
Unlike the other groups, the stoneflies simply crawl out of the water and find a sheltered spot to emerge, clinging to a piece of wood or rock. Then, the skin splits open and the adult pulls itself out, leaving the old skin behind. Adult stoneflies look pretty similar to the nymphs and are not very good at flying, avoiding it if they can – which may be why they go so unnoticed!
The life cycle of a stonefly: a nymph (Perla bipunctata), a larval exuvia (Perla bipunctata), an adult stonefly (Leuctra).
All these underwater creatures will be going through emergence throughout the summer months, so now is the best time to go looking for them! Look for the old larval exuvae on rocks, banksides and vegetation beside streams, rivers, ponds and pools. And see if you can spot the adults resting on nearby vegetation or making use of their newly unfolded wings.
The larval exuvae (old nymph skins) can be collected and taken home as a memory to the amazing creatures who once owned them. Just ensure the skin is definitely no longer occupied!
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