Royal terror - the Purple Emperor

The Purple Emperor is the holy grail of British butterflies, a truly magnificent creature capable of drawing an impressive crowd of loyal subjects all seeking an audience with His Royal Highness. The attraction stems from the Emperor’s stunning good looks combined with his quirky behaviour and elusive nature, which has driven enthusiasts to extreme lengths in their quest to lure him down from the treetops.

The iridescent sheen of royal purple is only present on the wings of the males, and then only when the light catches them at just the right angle. The larger Empress is less colourful but just as luxuriant in her chocolate brown robes. 

Both have intricately patterned under-wings featuring a large, orange eye-spot that mimics the piercing glare of the fearsome goshawk.  This provides an effective defence against would-be predators when the males come down to the ground to probe for essential minerals, their wings folded upright and ‘eyes’ on the lookout as they feast on mud and animal dung.  

Mating Purple Emperor butterflies © David Plummer

They follow a regular daily routine, usually descending for morning minerals between 10am and midday, and the Emperor’s fondness for fox poo and other unsavoury options has inspired the use of a range of disgusting baits to tempt him into view, from rotting fish to stinky cheese and even old nappies. This tradition dates back at least 250 years and some enthusiasts now keep their own recipes a closely-guarded secret.

The rest of the Emperor’s diet consists of sugary tree sap, which he will often indulge in to the point of drunkenness before staggering back to his tree-top throne. This is where he’ll spend the bulk of the day, perched on a leaf on the look-out for a passing Empress. He is fiercely territorial and will launch a vicious attack at anything and everything that enters his air space, not just rival males but other insects and even birds, ranging from blue tits to buzzards.

These aerial dogfights can soar to 50 metres above the canopy and are often the best clues to the Emperor’s presence, so it’s worth scanning the tops of oak, ash, beech and pine for the flutter and twirl of purple wings this summer.

Published July 2020, updated April 2025