Butterflies can loosely be divided into 3 camps regarding genetic interchange:
The first group comprises species such as the Painted Lady Vanessa cardui, the Small White Pieris rapae and the Pea Blue / Long-tailed Blue Lampides boeticus which are migratory in behaviour and cosmopolitan in distribution. Their nomadic nature brings them into fairly regular contact with distant "cousins" of their own species, so genetic interchange occurs frequently. A Painted Lady in Australia therefore is genetically almost identical to a Painted Lady in Europe, Africa, Asia or North America. Accordingly all races are designated as Vanessa cardui, and there are no recognised subspecies.
The second group comprises of endemics - species which are native to and confined to a limited area such as a particular island or mountain range. Examples include Calisto confusa which is found only in Haiti; Baronia brevicornis, found only in deciduous scrub forests of s.w. Mexico; Eresia sticta which is restricted to Costa Rica; and Henotesia comorensis - a butterfly confined to the Comoro Islands north-west of Madagascar. By definition endemics have no other races of their own species with which they can interbreed, so there are no subspecies.
The vast majority of butterfly species fall into the third group, which comprises those species which are quite widespread in distribution, but whose populations, due to changes in climate or vegetation have become isolated from each other for hundreds or thousands of years. Such populations have little opportunity to interbreed, so genetic interchange is minimal, and accordingly each isolated population develops its own characteristics. The Scottish race of the Large Heath e.g. lacks ocelli on the wings and is known as Coenonympha tullia scotica, while the race from Bosnia-Herzegovina has very prominent ocelli, and is recognised as a different subspecies Coenonympha tullia lorkovici.
The subspecies phenomenon is particularly prevalent in South America, where areas of rainforest have during several periods of the Earth's climatic history become isolated as a result of glaciation or desertification. The result of this long term separation of populations is particularly noticeable in the genus Heliconius. In the case of Heliconius erato there are no less than 29 subspecies, each with a different pattern. Each subspecies of erato corresponds in colour and pattern with one of the 29 subspecies of another Heliconius species - H.melpomene.