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Purple emperor (Apatura iris)

This is Britain's second largest butterfly and if you're ever likely to encounter one, you'll never forget it. It's an elusive species that spends most of its time in the woodland canopy.

Common name: purple emperor

Latin name: Apatura iris

Appearance

Caterpillars: bright green with yellow spots and diagonal yellow lines along sides.

Adults: large and dark with white banded wings. Males have a purple sheen, while females are brown with no purple sheen. They are the second largest butterflies in the UK (only the swallowtail is larger). Males are the size of a small bird and with iridescent purple splashed across its upper wings. 

Wingspan: 7.5-8.4cm.

Food plants

Caterpillars: goat willow is the most widely used foodplant although it lays eggs on grey willow and crack willow.

Adults: aphid honeydew and tree sap are the main food source, though they also come to ground to feed on animal dung and carion for salts and minerals. 

When to spot them

It can be spotted July to August.

Where to spot them

They are extremely elusive and occur at low densities over large areas, mainly in southern England. Despite a decline in the 20th century, it seems the purple emperor may be expanding its kingdom again, even into suburbia. South-central England is still prime territory, though.

Despite exotic looks, this species is as English as the oak tree it loves, haunting the high canopy of broadleaved woods. Your best chances of spotting them is early morning and again in late afternoon, when the males come down to the ground to feed on moisture from damp earth and animal droppings. Males also comb Salix bushes in the morning to flush out females. They later ascend into the treetops to mate.

Top Woodland Trust woods for purple emperor

We help support populations by protecting, restoring and expanding their native woodland. habitat. Try Wormley Wood, three miles north of the M25 in Hertfordshire, or nearby Tring Park, whose ancient woods and flowery chalk grassland are irresistible to butterflies. The emperor reigns too at Cadora Woods, in the Wye Valley in Gloucestershire, and at Piddington Wood in Oxfordshire, where both the brown and (seriously rare) black hairstreak are also on the wing.

Discover purple emperor in other woods too. To find woods near you, type your town or postcode into our search box.

Fascinating purple emperor facts

  • It's one of the rarest and most elusive butterflies in the UK and is sought after by butterfly enthusiasts.
  • The decline of purple emperor is thought to have been caused by the widespread and large-scale loss and fragmentation of ancient woodland.
  • Unlike other butterflies, purple emperor sometimes feed on dung, urine and decaying carcasses rather than nectar from flowers. This helps them gain vital salts needed in their diet.
  • Butterfly enthusiasts have been known to try to lure males down from the canopy with tempting treats such as banana skins and shrimp paste.
  • During July males congregate on particularly tall ‘master trees’ awaiting mates. The same trees can be used year after year.
  • Females either couple up with a male or swoop to the ground as a signal they have already mated.
  • The purple emperor is a member of the Nymphilidae family, which contains some of the biggest and most brightly coloured butterflies in the world.
  • Both sexes are almost black with white spots, but only the male has an iridescent purple-blue flash.