Most observers of dragonflies and damselflies restrict themselves to the final life period of the insect, which is when they are on the wing. This is understandable as this is when they are visually most appealing and obviously active. However, for most species breeding in the United Kingdom, a greater part of their life is spent under water.
The study of larvae allows the keen observer to extend the dragonfly and damselfly study season. Netting during the winter produces a poor return; larvae are most easily found from the beginning of March and most easily identified as they approach their final aquatic life phase. Up until the end of November netting can also be profitable as many early season dragonflies and damselflies have by this time, achieved significant size which allows for positive identification.
The study of larvae equips one with the skills to readily identify exuvia, the shed larval skin, often to be seen amongst emergent water side vegetation. Records of exuviae, their location, species and numbers are most eagerly sought by wild life recording bodies as they provide objective evidence of dragonflies and damselflies living out their full life cycle at the declared location.
The collection of exuviae requires little by way of equipment, only a few plastic tubes with blank labels on them, to write on the location and date, to negate the risk of forgetting what was recovered from where. Netting requires a little more investment in equipment.
Some practitioners wash the netted sample several times passing the sample between two white buckets removing detritus and as much silt as possible before placing the washed sample in a shallow white tray. The net, buckets and tray can be obtained from suppliers of ecological equipment, I get my buckets for free, from the local pub, they contain the oil used for cooking and are only thrown out when empty. The pub buckets come with a lid which can prove very useful. For a white shallow tray, those used for emulsion paint applied with a roller will do very nicely when empty and washed clean.
Another technique is to lay out a sheet of pale coloured plastic by the bank and just empty your netted sample complete with detritus onto it, now watch over it for a couple of minutes to see what crawls out, placing any dragonfly larvae in the shallow white tray, which of cause contains clean water. Other practitioners dispense with every thing except the net placing one hand under the netted sample and looking directly into the net to see what if anything can be seen climbing to the surface.
For most species of damselfly the caudal lamellae are a valuable aid to species identification. A word of warning, both size and colour can exhibit a wide range of variability for any species where banding is a declared feature. If still present the caudal lamellae of damselfly exuviae will be tightly packed together in a crumpled mass.
They can be easily separated. Take one hollow ground microscope slide and place the dissected caudal lamellae cluster into the hollow ground area and with an eye dropper add a small amount of water. Place to one side to soak for about two minutes. Then with a small artists brush separate out the individual lamellae retaining the median for inspection but in the case of Lestes species an outer is more commonly used.
Though it is possible to identify this group in the field it is recommended that as many key characteristics as possible are used to determine species identification. Exuviae readily lend themselves to being removed from site to a study location where x10 magnification can be employed and sample dissection easily achieved.
What follows is not a definitive key. The text and images only feature those species commonly encountered south of the Reading / Newbury M4 corridor. The intention is to help those intimidated by published keys to get started.