 |
| A.imperator ovipositing |
One of the largest dragonflies in Europe, the Emperor
Dragonfly Anax imperator has a range
from North Africa to the North Sea coast and most of the south of the British
Isles, and reaching east into the Ukraine.
There are around 30 species of Anax worldwide, mostly in the Old World, but there are some in
North America and there is one species native to Hawai’i. The genus belongs to
the widespread family Aeschnidae, hawker dragonflies. Hawkers get their name
from the behaviour – they catch and usually east their prey in flight and are
powerful fliers. Dragonfly genera can usually be identified by behaviour –
chasers and darters generally hunt from a perch.
 |
| A.imperator male |
All dragonflies are predators and as adults feed on smaller
insects, usually mosquitoes and flies but the larger species like Emperors will take
butterflies or even small species of dragonflies and damselflies. As aquatic naiads
they feed on smaller aquatic life and the larger nymphs may even take tadpoles
or small fish.
Dragonflies and Damselflies – the Odonata – are one of the
oldest lineages of flying insects. The oldest relatives of modern dragonflies
are known from the Carboniferous around 300 million years ago, these are the
griffenflies, “giant dragonflies” which in some species are believed to have
had a wingspan of around 70cm. How they managed to support such a gigantic size
with the high metabolic rate of dragonfly lifestyle is not certain, but it
probably is related to the higher oxygen levels of the atmosphere during their
reign, which at its peak may have reached 35%. This ended with the end-Permian
mass extinction during which global environmental changes resulted in a fall of
atmospheric oxygen levels to well below the present day level of 20%.
 |
| Anax junius |
Although dragonflies are thought of as exclusively
water-loving, water is only needed for reproduction. Once they have emerged as
adults they may hunt over other habitats entirely, hunting around trees in
woods, over fields, or preferring moorland heaths depending on the species. As
adults they are fairly long lived, and in the several months many species live
they can also travel long distances, as especially in tropical reasons they can
have regular migrations following the rains. They can also be found as vagrants
far outside their normal range – the North America Green Darner Anax junius has been found in the UK on
several occasions having crossed the Atlantic in the same way as many birds do.
Emperor dragonflies begin as eggs laid directly into the
water by an unaccompanied female. This last is slightly unusual – in many
species the male remains attached by his claspers to the female while she lays
her eggs in order to guard her from mating again. After an incubation period of
three weeks the eggs hatch into the aquatic naiads that feed on aquatic insects
and tadpoles for one or two years before climbing out of the water to moult
into the winged adults.
 |
| Teneral A.imperator |
On leaving the water the naiads may travel as far as 30m
from their pool and 5m up a tree before shedding for the last time and
appearing as an adult. With these large dragonflies even after emerging they
take one or two weeks to attain the full colours and becoming able to reproduce.
Males are very territorial and spend most of their lives in flight during the
day, even feeding on the wing.
 |
| Male A.imperator patrolling the pool where the female at the head of the post was egg laying |
(Green Darner, Emperor emerging photos from wikipedia, others are my photos)
