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Butterflies of Britain & Europe
 
Purple Emperor
Apatura iris LINNAEUS, 1758
Family - NYMPHALIDAE
subfamily - APATURINAE
Tribe - APATURINI
 
 introduction | habitats | lifecycle | adult behaviour
 
Purple Emperor Apatura iris, male, Hampshire, England
 
Introduction

The magnificent Purple Emperor is probably the British butterfly most admired and most sought by butterfly watchers, breeders, photographers and general naturalists alike. There are more stories told, and more myths about this species than any other. It is the second-largest species in Britain ( the largest being the Swallowtail ), measuring up to 85mm across the wings. The deep purplish-blue sheen on the wings of the male is produced structurally, as light is refracted by ridges on the wing scales, and is only visible from certain angles, and under certain lighting conditions.

Purple Emperor Apatura iris, male, Hampshire, England

Wishful thinking can sometimes lead less experienced butterfly watchers to mistake the White Admiral for this species. Both species are dark with white banding, both fly around oaks, and fly at the same time of year. The White Admiral however is smaller, far more graceful and delicate in flight, and has much more rounded wings.

In Europe the Purple Emperor can be confused with it's slightly smaller relative Apatura ilia, but that species has an orange-ringed black spot near the outer margin of the upperside forewing, and a narrower S-shaped white band on the hindwing.

The Purple Emperor is distributed throughout much of central Europe but is very localised in southern France, Spain and Portugal. It is absent from Scandinavia, peninsula Italy and the Mediterranean islands. Beyond Europe it's range extends across temperate Asia from the Baltic states to north-east China and Korea.

Habitats
 
In Britain the butterfly occurs as a breeding species in most of the larger woodlands in central southern England, where the larval foodplant grows along the edges of tracks. It formerly occurred over much of Wales and southern England, but is now confined largely to the counties of Wiltshire, Hampshire, West Sussex and Surrey, although a few isolated colonies occur also in Northamptonshire, Lincolnshire, Somerset and Devon.
 
Colonies are small, comprising only a handful of insects, but individual butterflies have a range that probably encompasses several hectares. The males in particular can be seen at least a kilometre away from the breeding areas, assembling at so-called master trees, of which there may be several in a large woodland complex. The master trees are usually mature oaks, but beech, aspen and conifers are also sometimes used. In each case the trees will be tall specimens, and located on high ground, typically on the brow of a hill.
 
At these master trees they indulge in spectacular "sorties" with other males, competing for the best vantage points. Groups of up to 4 males can sometimes be seen chasing in circles around the tree tops. Females are seen less often. They visit the master trees to find mates, and thereafter disperse to the egg-laying sites.
 
Lifecycle
 

The conspicuous domed eggs are laid singly on the upperside of sallow leaves. Broad-leaved sallow Salix caprea is used more frequently than the narrow-leaved S. cinerea.

 

In July 2005 I watched a female which in the course of 3 or 4 minutes laid about 10 eggs at various heights between 2 and 5 metres on broad-leaved and narrow-leaved sallows growing on both sides of a track in a Wiltshire wood. The eggs were laid on semi-shaded leaves in the interior of the trees. At other sites in Hampshire and Surrey, I have watched females ovipositing on low, sunlit leaves on woodland edge sallows; and at a thicket in north-east Hampshire I have seen a female oviposit at eye-level on a totally shaded broad-leaved sallow.

 

When first laid the eggs are entirely green, but after about 5 days they develop a dark purplish band near the base. They hatch after about 14 days, and the newly hatched larva makes it's first meal of the eggshell.

 

The young caterpillar is greyish-brown, and after it's first moult has 2 prominent horns on it's head. It feeds until October, entering hibernation in the 2nd or 3rd instar. It spends the winter in a vertical posture, resting on a silk pad spun in the fork of a twig of the foodplant, usually on the damper and shadier east side of the twig.

 

It resumes feeding in April, and when fully grown in mid-June is plump and green, marked along the sides with dark-edged diagonal cream stripes that perfectly simulate the veins of a leaf. Two "horns" project forward from the head, and the body is strongly tapered at the tail. It is quite unlike that of any other British butterfly or moth.

 

The caterpillar rests during daylight along the midrib on the upper surface of a leaf, and feeds on the tissue either side, leaving the midrib and leaf tip intact. At dusk it vacates it's resting place, and wanders all over the tree to feed. It lays an almost invisible trail of fine silk along it's route, and uses this as a map to return to it's "home" leaf before dawn.

The pupa, which wriggles frantically if touched, is a very beautiful shade of translucent silvery green, marked on the abdomen with short whitish diagonal dashes. It is slightly flattened in shape. The camouflage is so perfect that it is virtually impossible to locate, as it hangs suspended by the cremaster from a sallow leaf. The pupal stage lasts for about 14 days.

Adult behaviour
  

The butterflies emerge in late June and early July.

 

Although fairly widespread in central southern England, the Purple Emperor occurs at low densities, and is rarely seen unless deliberately searched for, although males have been observed on several occasions entering houses, shops or vehicles !

 

Purple Emperors spend most of their time resting high in trees, the males favouring oaks while the females more often rest in tall sallows. Females in particular may spend an hour or more on their tree-top perches, especially if the weather is cloudy or breezy. When the sun appears, even if only for a brief period, the males take flight and circle around the vicinity in search of food sources.

 

Both sexes will feed at honey dew ( aphid secretions ) where it coats the upper surface of sallow or oak leaves. Males often also feed at sap runs, or at carrion, but are most frequently encountered when feeding at fox scats or dog faeces from which they obtain essential alkaloids which are passed to females during copulation.

 

Neither sex visit flowers for nectar, although I once found a newly emerged female basking on a fleabane flower in a Surrey wood.

 

Purple Emperor Apatura iris, male, Hampshire, England

 

I once found 6 males feeding at the carcass of a roe deer that was floating in an open cesspit in a Hampshire thicket. The butterflies were so stupefied by their unsavoury meal that 2 of them remained on the carcass as I lassoed a rope around the antlers and hauled it to the edge of the cesspit to take photographs !

 

Mud-puddling typically occurs at about 8.30am on warm sunny mornings, or later if it is overcast. On cooler mornings puddling may not begin until 10.00am, and can continue until 12.30pm or later. Sometimes a male will spend an hour or more on the ground without moving. Further puddling occurs in the late afternoon at about 6.00 - 7.00pm if it remains sunny.

 

In some years, prolonged periods of dull or rainy weather occur during the flight season. Then, when the sun does briefly appear, a frenzy of courtship, mating and egg-laying takes place.

 

Copulation takes place high in the canopy, close to the master trees, in early afternoon. The pair remain joined until dusk, and probably until the following morning. Once, whilst watching a mud-puddling male in a Surrey wood, I saw a copulated pair float down from an oak, and settle on gravel. When I approached, they flew up into another oak, settling near the top of the tree. On another occasion a friend spotted a copulating pair late in the afternoon, at a height of about 6 metres in a spruce.

 

                                                       
Almost every British and European species of butterfly is declining rapidly in numbers, due in most cases to loss or degradation of habitats.
 
You can help to reverse the decline by supporting conservation organisations which purchase and manage habitats as nature reserves, and which lobby government at local, national and international levels, often very successfully, to bring about changes in farming, forestry and urban development policies.
 
Please contact the conservation organisations for advice on how you can help protect British and European butterflies and their habitats. You may be able to offer practical help e.g. by monitoring butterfly populations or helping to manage nature reserves. Donations to these organisations enable them to employ ecologists and biologists. Even if you are unable to provide such help, merely having your name on the membership list can be a powerful tool for conservation organisations wishing to demonstrate the levels of support they have for their policies.

 

 
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