Butterflies are rising in number and variety. The first survey of the Northern and Middle Blocks in 2005 recorded 13 different species; by 2020 we had 25. Surveys of the Southern Block, begun in 2012, increased the tally of butterfly species for the whole of Knepp to 37. The most recent addition to the list is grizzled skipper, a species that is declining in England.
Some of them are new arrivals, like the marbled white (first recorded here in 2005), the small heath (associated with many more habitats than its name suggests) and the dark green fritillary (first recorded here in 2015). Some – like green-veined whites, Essex skippers and, of course, purple emperors – have exploded in numbers. In 2015, Neil Hulme of Sussex Butterfly Conservation counted 790 small skippers – a spectacular increase from the 62 he counted the previous year which was, itself, a great year for butterflies.
Brown hairstreak is another species thriving in the Southern Block. Egg searches along the suckering growth of the blackthorn help monitor the numbers, where a huge increase of 1600% was seen in 2016 and resulted in an increase in the number of adults spotted in 2017. Usually a tricky species to see, this surge in numbers provided a real spectacle for visiting lepidopterists.
Knepp is one of a few locations in West Sussex for the declining white-letter hairstreak, a species which took a huge nose-dive in numbers as a result of Dutch elm disease. A diminutive species found in small colonies can be found in five locations, on old hedgerow elm, at Knepp.