From Piers

 

Iris is without doubt the most variable nymphalid to grace Albion's fair shores. It is, for some (as yet unexplained) reason, extremely prone to aberrations precipitated by environmental influences.

 

 

When one considers the quantity of iris aberrations seen in most seasons as a percentage of the total number of iris butterflies observed (and determined to be of typical form), the percentage of butterflies that are aberrant has to be significant.

This is brought into sharp relief when one considers the explosion of peacocks that we shall see this summer: There shall, without doubt, be one or two 'blind' examples around (much like there were in 2009); however, the percentage of aberrants in the Peacock shall be significantly less than are found in iris during an average iris season