Black Hairstreak colony found in Sussex. It sounds ridiculous, an early April Fools joke perhaps, but it appears to be true.
The butterflies are certainly there, on Ditchling Common, but how did they get there? The size and spread of the population suggests that the colony must have been established a long time ago. The best suggestion at the moment is that they were introduced in the 60s or 70s and have sat there, unnoticed for the past fifty years, slowly expanding their territory.
Fifty years without being noticed, it sounds unlikely but then these butterflies have a very short flight period, they stay mostly in the tops of trees, and this is probably not a well watched site for butterflies. With reports of 90+ Black Hairstreaks counted on one day this could well be one of the most numerous sites in the country.
There were a lot of people there today trying to photograph the butterflies and the area is getting a bit trampled. I expect it will be even worse by the end of the weekend. It's a pity that we do so much damage in our pursuit of a good picture.
For me the best aspect of the visit was that the butterflies were coming down onto the bracken and also nectaring on the brambles making them easier to see. On other sites I had only ever found them in the tops of trees or down nectaring at heights of around six to ten feet.
I understand further investigation of various records is being carried out in an attempt to identify the source of the introduction. However their presence in Ditchling Common raises a number of questions. This is a species that although considered scarce and very localised, does exist over a huge range through Europe, Asia, and as far as Japan. We assume that in the UK they can only exist in the belt of land through Oxfordshire, Northamptonshire and into Cambridgeshire but why should this be. Habitat requirements do not seem to be particularly onerous and could exist almost anywhere in the south of the country.
There have been many records for the Black Hairstreak from the South of England. A number of colonies were identified in the Surrey area in the 70s and the assumption was made that these had spread from an introduction near Cranleigh in 1952 *. Possible but this is a highly sedentary butterfly. These colonies were all viable and only appear to have been lost through habitat destruction.
Perhaps the ramblings of a half informed amateur, but could there be more colonies out there in the South of England waiting to be found.
I have no qualms about adding it as number 47 on my Sussex list. People will argue the merits of introducing a species into an area where it has not existed before but these have now survived for about fifty generations and they still look to be prospering. That's good enough for me.
*(PDF) Black Hairstreak. Available from: https://www.researchgate.net/publication/275958378_Black_Hairstreak [accessed Jun 14 2018].