Identification Issues
British and Irish Butterflies: an introduction to the concept of subspecies and forms.
To many beginners in the study of butterflies and moths the concept of a 'subspecies' is rather bemusing. The authoritative literature is littered with terms such as this along with 'race', 'form', 'variety' and 'aberration'. Here I shall try to explain what these mean in practical terms for the field naturalist and then describe the features that make each of the British butterfly subspecies and common forms recognizable.
An aberration (abbreviated 'ab.') is an individual variant, resulting from genetic mutation or extreme environmental anomalies, which can occur erratically within any population of a species. They are rare and are sometimes bizarre in appearance. A useful example would be that of a gynandromorph where one half is of male coloration and the other half female. In evolutionary terms such individuals are in a cul-de-sac and usually provide future generations with little, or no, selective advantages. However, for the butterfly-watcher, imagine the wonderment of finding a gynandromorph Orange-tip. From aberration we go to the next step in the evolutionary ladder to form.
A form (abbreviated 'f')is distinct in appearance from typical individuals and can occur within any population at various frequencies. The classic example is that of the Peppered Moth (Biston betularia (Linn.)). Here the typical form is white with black speckling. A form known as carbonaria Jordan is predominantly black and, during the industrial revolution of the early 19th century, this colouration gave individuals a selective cryptic advantage when resting during the day on grime-covered trees. Individuals of the typical form were easy prey for predators such as birds and the formerly rare black form became dominant in areas where industrial pollution was at its greatest. Nowadays, thankfully, soot-covered trees are rare and so, as a consequence, is form carbonaria of the Peppered Moth. In the butterflies such forms are unusual but can, in some species, occur regularly. Good examples are the 'Greenish' Silver-washed Fritillary and the 'Helice' Clouded Yellow that constitute a percentage of female individuals within the species and the 'Blind' Ringlet that can occur frequently over a number of years at some localities. Where a form is found regularly at certain geographical locations (sometimes referred to as 'races') we are perhaps on the next step of the ladder where we find subspecies.
The subspecies (abbreviated 'ssp' and sometimes referred to as 'race') is a very important taxonomic division. Here we have a form that predominates within a population, in most individuals is distinct in appearance and is genetically isolated from neighbouring colonies of either the typical form or other subspecies. Because of their isolation, and the selective environmental pressures placed upon them, they might be described as being only one evolutionary step away from being a species in their own right. Of course, such a process is ongoing and probably takes many millennia to come to fruition. Along the way there are many 'grey areas' and different authorities are sometimes at loggerheads with assignation to subspecific status. For the purposes of this project I have decided to conform with the latest opinions of the highly respected lepidopterist John Bradley (Bradley, J.D. (200) Checklist of the Lepidoptera Recorded from the British Isles). Within the British and Irish butterflies subspecies often inhabit remote areas and are on the very edge of the species' geographical range. For this reason they respond very quickly to changes in their ecosystems and are therefore extremely useful environmental watchdogs. We hope that this website will encourage its readers to visit their haunts and record their numbers.
Monitor updates on this page for descriptions of the visual differences between the British and Irish subspecies and common forms.
