Fig 2.6 Damselfly (Zygoptera) Nymph (After photograph by A. Chalkley)
What the nymphs of dragonflies and damselflies have in common is a unique
adaptation for their carnivorous mode of life. This is the 'mask', or labium, which is a
large, hinged structure, usually kept folded up under the head of the nymph. When
potential prey approaches, however, it can be extended very rapidly, and bears
articulated gripping parts at the front end. Once captured in this way, the prey is brought
back to the mouth-parts to be consumed. In both dragonflies and damselflies. the
details of the structure of the labium are important for identification.
There is no resting, or pupal, stage in the life history of Odonata. When fully-grown
the nymph leaves the water, usually by climbing the stem of some emergent plant. This
usually takes place at night or in the early morning. The exoskeleton splits at the back,
behind the head, and the adult dragonfly gradually emerges. It is initially soft, and pale-
coloured, and it hangs from the cast-off'skin' (exuvia) or from a nearby leaf or stem until
its wings have fully expanded. After some hours, the insect is capable of making its
maiden flight.
The Ecology of Dragonflies
What has been said so far about behaviour and life-history suggests quite a lot about
dragonfly needs if they are to flourish in a given area. First, and most obviously, they
spend the early part of their lives under water, and their adult lives on land or in the air.
This means that they are dependent on a satisfactory quality of aquatic and adjacent
terrestrial environment. Moreover, since eggs have to be laid in or very close to the water
by the adults, and also fully grown nymphs have to emerge from the water, the character
of the transitional zone between land and water can also be crucial to survival.
Since dragonflies are quite ferocious (and usually indiscriminate) predators both as
nymphs and as adults, their presence at a site is a good indicator of a rich and diverse
invertebrate fauna. The smaller nymphs feed on microscopic Crustacea, insects and
other invertebrates, whilst the larger Anisopteran nymphs may take tadpoles, small fish
and other nymphs. The adults usually capture their prey in flight, and will take other
insects such as gnats, mayflies, beetles, and even quite large butterflies. But in all stages
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