Looking at the skins of dragons

One of my tasks over the coming months is to go through the many hundreds of damselfly cases that have been collected as part of our reed warbler study. The warblers feed their young on a range of insects, damselflies included, and we need to secure a measure of how the availability of these changes throughout the reed warbler breeding season. The cases are collected from a standardised area of reed bed on a weekly basis, a task that can take several hours of careful searching.

As you probably already know, damselflies spend a greater part of their lives in water as larvae, emerging only when they are ready to transform into an adult. At our site, with its extensive fringing reedbeds, much of this emergence takes place on the reed stems themselves, the larval damselfly hauling itself out of the water ahead of the transformation.

The delicate case left behind after emergence is known as an exuvia (plural exuviae) and this forms a perfect replica of the larva, still showing a series of features that can aid identification. Thanks to the incredible efforts of Steve Cham, we now have two guides dedicated to the identification of dragonfly and damselfly larvae and exuviae, Simple to use and full of illustrations the guides are going to be well-thumbed this year as I work my way through the hundreds of sample tubes packed with specimens.

These are not be the only samples to be tackled this season, as we also have measures of the availability of other insects, notably small flies, collected via a series of pan trans. These traps, which take the form of yellow bowls placed on posts and which are filled with water, sample flying insects using the reed beds. Not only do we plan to examine the seasonal availability of potential reed warbler prey but we also want to look at how it varies across the site. This should enable us to relate characteristics of individual nesting attempts to prey availability and to establish whether some parts of the site are better for breeding reed warblers than others. The answer to that question is some way off, however, not least because we have all these specimens to go through first.

Changing times for dragonflies

Last summer was, by just about every measure, a poor one for our wildlife. Bird populations took a hit from a poor breeding season, butterflies were notable by their absence and many of our invertebrates fared badly under the cold and wet conditions. Such poor summers are, one would hope, the exception rather than the rule, so there is the opportunity for things to bounce back if they have a better breeding season this year. It is important, however, to view such short-term impacts against the long-term pattern of a changing climate and increasing pressures on the land. Some species will benefit from a changing climate but others will lose out and there is already evidence of differences in how well particular species, or groups of species, are likely to fare.

As a group, dragonflies appear to be doing well and they may be one of the winners from a changing climate. A number of species are expanding their breeding range northwards across Britain and others are in the process of colonising our region. Species like the small red-eyed damselfly, which first reached Britain in 1999, are now well established and spreading. The southern emerald damselfly, which exhibited a major influx at Winterton last September and which has been recorded from the site in six of the last 13 years, was noted egg-laying here in 2012. It has already bred at sites elsewhere in south-east England, most notably at Cliffe in Kent. The willow emerald is another recent colonist, now established across parts of Norfolk and Suffolk.

There are several other dragonflies that reach our shores from time to time, originating from populations breeding elsewhere in Europe and often far to the south. Such arrivals underline the dispersal powers of these often robust insects and the pattern of migration exhibited by some species. A good example of this comes in the form of two Suffolk records of large white-faced darter from 2012. This species has a relatively southern range compared to related species, and most populations tend to be rather small. An unexpected and rather large movement of this (and related species) was noted in 2012, with individuals recorded from sites across north-west Europe, including the British records from Dunwich Heath and Landguard. Such movements are likely to result from a good emergence, coupled with favourable weather conditions, that deliver individuals to areas beyond their normal range. If individuals arrive in good numbers at sites where suitable habitat is available then there is a chance that breeding may take place and the species become established. Under a changing climate, warmer conditions in Britain may further favour the establishment of more species with a formerly southern distribution, so it is very much a case of watch this space.

Transformation

I have been fascinated by the transformations of butterflies, moths and dragonflies since childhood; that one body form can be turned into something completely different is amazing. While the changes in butterflies are striking enough, it is those of the dragonflies that I have always found the most interesting. The transition from an aquatic larva to a winged, non-aquatic adult is truly remarkable. In some ways the metamorphosis of a butterfly appears to be a passive process, the larva settling down in a sheltered location to become a pupa from which an adult will ultimately emerge, often many months later. In dragonflies it feels so much more active and immediate, the adult emerging from a larval form that has itself only recently emerged from the water. Of course, this is an illusion in the sense that it is the adult itself, held within its old larval skin, which drags itself from the water to clamber up a suitable stem.

Many of the British dragonfly species (and I include damselflies under this broader title) emerge from mid- to late-morning, which offers the interested observer with the opportunity to witness the breathtaking series of behaviours which deliver the winged adult into the world. A few of the larger species, however, leave the water at dusk, completing their emergence by the early hours. Most individuals select an emergent plant as their place of transformation, clambering up to a position well clear of the water. Once a suitable position has been found, the larva attaches itself head up and then proceeds to swing its body about in a characteristic and jerky manner. It is thought that this behaviour, which also includes various circling leg movements, allows the dragonfly to determine that it is securely attached to its support and also that there are no obstructions close by that might hinder the expansion of its wings. If the wings push up against an obstruction during their expansion phase then they can be severely damaged.

The first stage of the transformation involves a switch from aquatic respiration to aerial respiration. The cuticle then splits and the head, legs and thorax are pulled clear of the larval skin. This appears to be a demanding process because it is invariably followed by a long period during which the insect remains immobile and resting. The abdomen is then withdrawn from the skin and the process of expansion begins, with both the wings and abdomen very slowly increasing in size. Once the process of expansion is complete, the now fully formed adult remains on its support until it is ready to take to the air for its maiden flight, leaving behind the larval skin and all evidence of its once aquatic lifestyle.

Dragonflies need your help

There have been a few chilly mornings down on the fen over recent days; the air crisp but the clear blue sky heralding what will be a warm day ahead. Here and there on the lush growth are the fragile forms of dragonflies and damselflies, the first of this season’s new generation, struggling to warm up before they can venture forth. These primitive forms seem sluggish at this time of day but once their bodies are up to temperature they will become the insect masters of the air, voracious predators with a formidable reputation.

Roosting overnight in the vegetation has clear advantages, not least the avoidance of most predators. However, the limp bodies of many dozens of damselflies hang contorted in the webs of a myriad of spiders. A closer inspection reveals these to be Azure Damselflies. The emergence of these tiny creatures must represent a seasonal bounty for the spiders. Elsewhere on the fen, along one of the more sheltered rides, are Hairy Dragonflies, a species of early spring and one of the first to be on the wing. The males have fine white down on the top of their thorax, between the huge eyes and the powerful wings. These are robust creatures, the males actively patrolling low over the vegetation.

Seeing these dragonflies is all the more important this summer because the British Dragonfly Society has just launched a new National Dragonfly Atlas. Fieldwork will continue over the next five years with the aim of building up a picture of how our various species of dragonfly and damselfly are doing. It is fair to say that a new atlas is urgently needed. Changes in the quality of wetland habitats, coupled with global warming, mean that we really need a new stock take of these wonderful creatures. Several new species have established themselves here since the last atlas and others have declined in number, maybe by more than we realise. The beauty of the new atlas is that anybody can get involved. This means that any records that you can collect of dragonflies can be fed into the atlas. All you need to do is record which species you saw, when and where you saw it and then submit this, together with your contact details, to the British Dragonfly Society (www.dragonflysoc.org.uk). Of course you need to be able to identify which species you saw. If this is something that you are unable to do, then simply take a photograph of the dragonfly and send this in with the other details. Experts at the society will be able to identify it for you and then add the record to the atlas. Now where did I put my notebook?