To this tribe belong the Dragon Flies, the largest and most beautiful
members of the whole order.
About 1,500 species have been described from various parts of the
world, and of these about fifty are known to inhabit our own country.
Their habits are very much alike. The insect passes all the earlier
stages of its existence in water. The _larvæ_ are most voracious
creatures, and are undoubtedly the most predaceous of insects. The
apparatus by which they capture their prey consists of a peculiar
modification of the _labium_.
When full grown the _larvæ_ crawl up the stem of some aquatic plant
out of the water, and after resting there for a longer or shorter
time the skin splits open along the thoracic region, and the perfect
insect by degrees struggles out of its investment, and when the wings
are dried it starts off to continue the same scene of rapine which has
characterised its subterranean existence.
The perfect insect may be seen hawking about for insects in the
neighbourhood of pools in all fine weather during the summer and
autumn months. In dull weather, however, they usually remain at rest on
the leaves of plants and trees, etc. The eyes of Dragon Flies are most
beautiful objects when viewed under the microscope; they are composed
of a great number of facets or lenses. In one species of Dragon Fly as
many as 10,000 of these facets have been counted in each of its eyes.
Besides these compound eyes most dragon flies have additional eyes,
called _Ocelli_, which are situated on the top of the head; they are,
however, quite simple.
It is commonly thought by persons who are not naturalists that dragon
flies sting; such an erroneous idea we take the opportunity to correct.
[Illustration: Fig. 54.--Libellula Depressa.]
The _Ornoptera_ are divided into two principal families.
_Family 1, Libellulinæ._--To this family belong all the great dragon
flies, mostly thick-bodied insects. It is subdivided into four
sub-families.
To the first sub-family, the _Libellulidæ_, many common and familiar
dragon flies belong. The best known is what is vulgarly called the
"Horse-stinger" (_Libellula depressa_), an insect about two inches
long, with a rather depressed abdomen, which is yellowish-brown, with
yellow spots on the sides in the female, and coated with a beautiful
violet-blue powder in the male.
It may be seen almost everywhere, hawking for flies about rivers and
ponds, during warm weather.
The second sub-family, the _Cordulidæ_, contains four British species,
of which the beautiful _Cordulia metallica_ is the typical example.
The _Æschnidæ_ contain some of the largest members found. The great
dragon fly (_Æschna grandis_) is one of these. It is nearly three
inches long and four inches in expanse of the wings, and is of a light
rusty-brown colour with a few pale markings.
Of the _Gomphidæ_ only four species inhabit our own country.
_Gomphus vulgatissimus_ is a black insect, nearly two inches long, with
yellow bands on the thorax, and a line of the same colour along the
back of the abdomen.
_Family 2, Agroninæ._--This family contains a number of slender-bodied
insects. There are two sub-families.
The _Agrionidæ_ are a very numerous group. The typical form, _Agrion
puella_, which is a beautiful, slender creature, measures about two or
two and a half inches in expanse of the wings. The abdomen of the male
is banded with azure blue, that of the female being brassy-black.
The _Calopterygidæ_ contain only two British species--viz., _Calopteryx
virgo_ and _C. splendens_.
[Illustration: Fig. 55.--Calopteryx Virgo (Male).]