www.ukbutterflies.co.uk

Quite a few silver-washed fritillaries about at Chambers Farm Wood, Lincolnshire, today, fresh and well worn. But one stood out like a sore thumb.

Valezina

Yup. They refer to it as a form rather than an aberrant. They are not especially rare although you tend to only see one or two every so often.

Thank you, I had been hoping for an aberrant as we've been finding quite a few there in recent years, wishful thinking, but I'll settle for this

Interestingly, the older butterfly textbooks stated that the valesina form occurs mainly in south-central England, with Hampshire being the UK valesina stronghold - this form was said to be rare further north. However, several have been seen in Lincolnshire in recent years. The gene that controls this colour form is carried by the male, but only produces the phenotype in females, so clearly the recent spread of the species northwards and eastwards has brought the relevant gene with it. Genetically speaking the gene that codes for valesina is dominant over the "normal" form, so there must be some pretty heavy selection process/processes working against the valesina form, otherwise it should be far commoner than the usual orange form!