Anax imperator
Anax imperator Leach, 1815
Local names: Blue emperor, Große Königslibelle, Grote keizerlibel, Anax empereur, Blå kejsartrollslända
Species Information
Description
A large, common and conspicuous dragonfly. Patrolling males are easily recognised by their size, unmarked green thorax and blue abdomen with a black mid-dorsal stripe.
The thorax on Anax imperator is uniformly green, much like Aeshna viridis, but A. imperator is markedly bigger. No antehumeral stripes are to be found on either males or females. The females and immature males have a more greenish abdomen. Females might also have the same colouration as the males, with a blue abdomen. In some population this blue form is the norm among the females. The eyes are green with at most a brown hue. Female eyes have a yellow hind edge. Wings are clear with a yellow leading margin. Pterostigmas are brown.
S1 is always green, never brown or greyish (as on A. parthenope or A. ephippiger). A thin yellow ring on S2 characterises the still immature individuals (but is also present on mature males of A. parthenope). Males of A. imperator can be distinguished by the black pentagonal marking on the frons. Females has an absence of occipital tubercles.
Size
Habitat
Generally common or very common in standing waters at low altitudes, but also occurs in slowly running waters. Prefers unshaded and well-vegetated habitats. It is found in a wide variety of natural or man-made habitats such as lakes, fens, bogs, quarries and larger garden ponds.
Distribution
One of the most common and widespread species in southern and western Europe. It is still common in south-eastern Europe and parts of Turkey. It is scattered in Russia and Kaukasus. In the north its range seems to be constrained mainly by summer temperatures and it is absent from Ireland, Scotland and northern Fennoscandia. However it is currently expanding rapidly northwards with the climate warming.
Flight Period
May to October
Behavior
Restless patroller and very aggressive against any competition. Catches surprisingly large prey (like Libellula quadrimaculata) and often eats them in mid flight. Males patrol over open water, often further out and at higher altitudes than other Aeshna males.
Similar Species
Anax parthenope, Anax ephippiger, Aeshna viridis, Aeshna affinis
External Links
Genus: Anax
Anax is a genus of dragonflies in the family Aeshnidae. The name derives from from Ancient Greek ἄναξ anax meaning lord, master or king,
Identification
The Anax species are among the largest dragonflies. Almost all have a uniformly brown or green thorax, and a green, blue or brown abdomen. Anax immaculifrons, being the exception, has broad black thorax bands and a striking black-and-yellow ringed abdomen. The males, and all female aeshnids, lack auricles on S2 as well as anal triangles.
Separation from other genera
Other aeshnids have banded markings on thorax and their abdomen is basically dark with a mosaic of paired coloured spots. The males of these genera have auricles and anal triangles. A. immaculifrons may look like a Cordulegaster in flight,
but has a thicker abdomen.
Separation of the species
Flight identification can be difficult, with most characters overlapping (A. immaculifrons yet again being an exception). The colour of the abdomen, thorax and eyes vary, often with age. Young individuals might have greener body, turning more brown or blue with later age. In hand some important characters are the frons markings, male appendages and presence of occipital tubercles in females.
Anywhere near the Atlantic coast, one should look out for A.junius, an American migratory vagrant, rarely found in Europe but occasionally found far from home.
Behaviour
All species are powerful and fast flyers. Males of most species patrol effortlessly, usually a bit out over larger waterbodies. When resting, for instance during poor weather, they often rest low among waterside vegetation. They do this hanging vertically.
Family: Aeshnidae
The Aeshnidae, also called aeshnids, hawkers, or darners, is a family of dragonflies. The family includes the largest dragonflies found in Europe and North America and among the largest dragonflies on the planet.
Description
Common worldwide or nearly worldwide. Genera are Aeshna and Anax. The African Anax tristis has a wingspan over 125 mm, making it one of the world's largest known dragonflies. Most European species belong to Aeshna. Their American name darner stems from the female abdomens looking like a sewing needle, as they cut into plant stem when they lay their eggs.
The dragonflies mate in flight. The eggs are deposited in water or close by. The larvae (nymphs or naiads) are generally slender compared to those of other families, with a long and flat extensible lower lip (labium). The larvae are aquatic predators, feeding on other insects and even small fish.
The adults spend large amounts of time in the air and seem to fly tirelessly. They can fly forwards or backwards or hover like a helicopter. The wings are always extended horizontally.
The abdomen are mostly colored blue and or green, with black and occasionally yellow. The large, hemispherical, compound eyes touch in the midline. Individuals of this family have an extremely good sight, and are voracious insect predators.
A proposal has been made to split this family into Aeshnidae and Telephlebiidae.
The name may have resulted from a printer's error in spelling the Greek Aechma, a spear. The spelling Aeschnidae has been intermittently used over a period of time, but is now abandoned for the original name Aeshnidae. However, derived genus names (such as Rhionaeschna) retain the 'sch' spelling, as this is how they were first cited.