The abdomen is usually held straight, but can also be curved round under the insect,
which may well explain the widespread (but completely false) belief that dragonflies
can sting.
They can. incidentally, give the unwary captor a slight nip with their mouthparts! The
shape and patterning of the abdomen is usually very important for identification, but
there are two sources of confusion in this. One is that the males and females of most
species have different colouration (usually the males have brighter, and more
contrasting colouration), and there may be several different colour-forms of the same
species (often restricted to one sex). Ischnura elegans (the Blue-tailed Damselfly) is
especially variable. The other source of confusion is that when they first emerge,
dragonflies do not immediately take on their full adult colouration. 'Immature' (teneral)
adults should not be used by the beginner for purposes of identification where
alternative, fully mature specimens are available. Ageing specimens, too. can undergo
gradual colour-changes (sometimes females approach the male colouration, as in some
Sympetrum species) which can be confusing to the beginner.
Dragonfly colouration is an interesting topic in its own right, there being three basic
ways in which colour-effects are produced. Generally the colours are produced by
pigment situated either within or just below the outer cuticle of the body. In other cases,
the distinctive 'metallic' colours are produced by the structure of pigment-grains which
split up incident light producing what are known as 'interference-effects'. The third
mechanism of colour production is the exudation of a pale blue (or white)
'pruinescence' (rather like the bloom on a plum) onto the outer surface of the body. This
accounts for the pale blue colouration of fully mature males of such species as Libellula
depressa (the Broad-bodied Chaser) and Orthetrum cancellatum (the Black-tailed
Skimmer).
The abdomen also carries the main reproductive organs in which, again, the
dragonflies are unique in the insect world. As we shall see. the mating position of
dragonflies is distinctive. At the hind tip of the abdomen are the anal appendages.
Females of both dragonflies and damselflies have one pair of appendages. Male
damselflies (Zygoptera) have two pairs ('superior' and 'inferior'), whilst male dragonflies
(Anisoptera) have one pair of superior and a single inferior appendage. The shapes and
sizes of these appendages are distinctive for each species, and they are indispensable for
the definitive identification of some species. The males transfer sperm from the sperm-
duct near the tip of the abdomen to a set of 'accessory genitalia' situated on the ventral
surface of the abdomen on the second and third segments, and it is from here that the
female acquires the sperm for the fertilisation of her eggs. The females also have a set of
structures (ovipositor) for egg-laying towards the tip of the abdomen on the ventral
surface.
The Classification of Dragonflies
Dragonflies in the widest sense of the word together make up the insect order
Odonata. This order is further subdivided into two groups of species. The generally
smaller, more delicately built species, in which the fore- and hind-wings are similar in
shape, and in which the typical resting position is with wings 'folded' along the line of
the body are known as the 'damselflies'. Zygoptera. The larger, more robust species, in
which the fore- and hind-wings are differently shaped, and in which the resting posture
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