Purple emperors are one of the most astonishing successes of the rewilding project. None having been recorded here in the recent past, Knepp is now home to the UK's largest colony of this spectacular butterfly.
Second only in size to the swallowtail, the emperors were first seen at Knepp in 2010. The males display in the canopy of the oaks, marking out their territory in competition for females. They are surprisingly aggressive, and will chase away anything else that flies – including birds.
It is our emerging sallow scrub that has attracted them here. The females lay their eggs on a particular type of sallow leaf. This only occurs on a very low percentage of hybridised sallows. Large areas of sallow are therefore needed in order to encourage large populations of purple emperors. However, in our modern landscape, sallow is rarely tolerated and consequently it is unusual to see this lovely iridescent purple butterfly in the high numbers we experience at Knepp. On a single day survey in July 2018 we recorded a count of 388 individuals, double the number of the previous year which, itself, smashed national records.
Unlike other butterflies, the purple emperor has decadent tastes. Shunning flowers, it feeds on fox scat and sap runs from wounds on the oak trees, behaving more like a tropical butterfly.
Previously considered a ‘woodland’ species, the emperor’s success in the sallow scrub at Knepp is revealing new insights into its behaviour and habitat preferences.