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Butterflies...flowers that fly and all but sing

Robert Frost

The purple emperor, Apatura iris, is a truly magnificent yet rarely encountered butterfly of oak woodlands across Europe, Russia and Scandinavia. Rejecting the more common butterfly sweetmeats of nectar and pollen, the purple emperor dines on the honeydew secreted by aphids in the forest canopy and is, therefore, rarely spotted by we terrestrial creatures whose eyes are more firmly fixed at ground level.

Classification

Purple emperors are the largest British woodland butterfly but are not known as common as they are rarely seen and fairly secretive. What at first appears to be a dull brown or black, (although distinctively large) butterfly will suddenly be caught in sunlight and the incredible purple iridescence of their wings will be revealed in a brilliant flash. Only the males display the characteristic purple sheen, females having duller markings which probably accounts for their ‘elusive’ status. The hind wing has a distinctive orange ringed eye and males have orange proboscis.

The males live at the tops of oak trees where they mark out a territory and then display, hoping to attract females. Eggs and caterpillars are incredibly well camouflaged, hidden high up in sallows and very difficult to find. Not something that you are going to find flitting through your garden unless you’re very very lucky!


Location
In the UK purple emperors are mainly confined to the south of the country, their stronghold being Wiltshire and Hampshire. However, recent species specific research suggests their range is quite a lot wider, but they are not easy to spot and dedicated purple emperor safaris are beginning to happen more widely throughout the southeast and south west, spearheaded by Butterfly Conservation, the leading British Lepidoptera charity. (See this link for information on this project)

Habitat
These butterflies favour large areas of woodland where there is a high but undulating canopy and plenty of sallow which is the primary food plant of the caterpillars. The woodland can be scrub (a mixture of low growing shrubs and small trees such as hawthorn, blackthorn and elder), but will need some tall standards within it. Colonies have also been known to occur in clusters of small woodlands where they can fly between the copses.

Breeding
Purple emperors require a ‘master tree’ where the males will set up a territory and display to the females which is normally an oak, but ash trees can also be used. After waylaying a female and mating with her, she will seek out a sallow and lay her eggs on the shiny upper layer of the leaf. Purple emperors are on the wing from late June to August and mating and egg laying takes place in this time.

Once the eggs hatch, the small green caterpillars proceed to decimate the top leaves of the sallow, disguised perfectly as sallow leaves themselves. They munch throughout the autumn, hibernating over the winter in cracks and crevices within the tree bark and even in the buds themselves, emerging in April to feast on the new leaves.

Come June the caterpillars have built up enough energy to pupate, and dangle off the willow twigs like fallen leaves, emerging in the latter half of the month to court and reproduce.

Feeding
The caterpillar of the purple emperor (see links below for pictures) looks amazingly like the leaves of the sallows on which they feed. The most favoured tree is the goat willow, but also the grey willow and less frequently the crack willow will home these small green horned beasties.

Adult butterflies exist on a diet comprised of the secreted honeydew of aphids, found on the leaves and bark of trees, although the emperor butterflies feed almost exclusively up in the canopy. To supplement this they will come down from the trees to feed on the choice delights of animal dung and rotting carcasses in which they find important minerals and nutrients. Apparently some surveyors have also found them particularly attracted to sweaty humans and smelly cheese!

Other Tidbits

  • In 2005 the first record of a second brood of purple emperors was recorded in Storrington, Wiltshire. This was the first time two batches of eggs hatching in one year has been recorded, one newly emerged male seen winging his way lazily along on a bright day in early October.
  • Male behaviour changes according to population density. The purple emperor can maintain very low populations, and this is one of the reasons they are so hard to spot. Only when there are lots of males vying for a female’s attention will a master tree be easy to find due to the cloud of males displaying around it. In low population areas, trying to spot a couple of males 60 foot in the air disguised by oak leaves only going to inspire the most ardent enthusiast!
  • Although under recorded due to its secretive nature, the purple emperor, along with all of our British butterflies, has been in decline over the past 50 years due to changes in agricultural practises and the destruction of woodlands.
  • Most butterfly photographers report stories of purple emperors landing on their arms, wet with sweat after having waited around at the bottom of a master tree in blazing sunlight trying to photograph one. Obviously, although a pleasant experience, trying to take a photograph when the subject is crawling about on your appendage is not an easy experience!

If you are out walking in the woods late June and July, take a pair of binoculars with you. Who knows? You could be responsible for rediscovering a colony of Purple Emperors in your area. Contact Butterfly Conservation for more details.

Sources:
http://www.ukbutterflies.co.uk/species.php?vernacular_name=Purple%20Emperor
http://internt.nhm.ac.uk/cgibin/fff/glob.pl?report=Fauna&Fauna.FaunaNo=35.0
http://www.butterflyconservation.org/species/bdata/purple_emperor.html
http://www.butterfly-conservation.org/species/master_tree_project/index.html

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