The purple emperor (Apatura iris) is not the rarest butterfly in the UK – that rather dubious accolade would go to the high brown fritillary although there are far too many other species, such as the black hairstreak, in close contention.
But the purple emperor is one of the largest and certainly one of the most impressive. It is a woodland butterfly, favouring deciduous woodlands with a dominance of oak or beech although a good supply of willow, the larval foodplant, is another requirement. Perhaps it is this habitat, the high treetops in mature woodland glades, which makes the species all the more regal as it descends and deigns to be appreciated before ascending once more.
They are found in mature woodlands through southern England with occasional colonies elsewhere in the country and, luckily, one of these is only a 40 minute drive from Grantham.
We took a drive down to Fermyn Woods on Saturday, arriving around 10am, and were lucky enough to spot a male purple emperor settled upon a damp digging to the side of the trackway within 100m of the car. The males are seen most frequently as they come to ground to take moisture, nutrients and salts from damp ground and animal droppings – a behaviour which spoils the regal image just a little.
The remainder of the time, the adults spend high in the canopies, feeding upon the aphid honeydew and this is generally where the females will stay – they could be seen occasionally breaking the canopy cover before returning and remaining on high.
The purple emperor is very darkly coloured, almost black, with patterning of white and orange on the top of the wings. The underside are a magnificent rich marbled motif of brown and white, almost as spectacular as the open wings. But when the light catches the wings of the males, the reason for their name becomes apparent as a sheen of purple washes across the wings, marking this out as one of the most spectacular butterflies you are likely to encounter.
As we walked amongst other enthusiasts watching the paths and the canopies, we saw another two in flight, along with many other butterflies including white admirals, ringlets, countless skippers and speckled woods.
The best time to see the purple emperors is around now – the peak date for sightings is given as the 13th July – and they are generally to be found on the ground during the morning when the sun begins to heat through. The ride which runs from east to west through the middle of the woods was the place to be although the woods have a network of paths which are worth exploring for their range of wildflowers including meadowsweet, perforate St John’s wort, hedge woundwort and red campion.