Steven Cheshire's British Butterflies
British Butterflies: Species: Aberrations, forms and variations
A male Adonis Blue ab. krodeli.
A male Adonis Blue ab. krodeli.A normal male Adonis Blue for comparison.A normal male Adonis Blue for comparison.Find out more about the Adonis Blue.

The Cockayne collection of British butterflies held at the Natural History Museum include images of many named and unnamed aberrations.
What are aberrations?
An aberration is a variation in the wing pattern of a butterfly species which is different in some way to the normal pattern. This can occur as a genetic or environmentally induced variation of the usual form of the species. Aberrations are generally very rare. Some recur on a fairly regular basis and as a result, many have been specifically named.

How do aberrations occur?
Butterfly aberrations occur for a variety of reasons, generally, extreme temperature changes especially while the butterfly is developing during the pupal (chrysalis) stage may cause aberrations to occur. Very cold conditions can produce very dark forms of some species while heat shock (sudden temperature changes or extreme temperature) may cause dramatic changes in wing pattern and colouration.

Personal experience in the field has shown that some aberrant forms occur where butterflies appear to have deformed/damaged wings as a result of the pupa becoming damaged as the butterfly developed inside or by a minor bacterial/fungal infection during the pupal stage.

What are forms and variations?
These are common occurrences within a species and in general are a consistent variation which is often limited in its distribution. Variations may occur due to local geography, climate and population interaction.

A good example of general butterfly variation is the Small Copper Lycaena phlaeas which also has a common variation known as Lycaena phlaeas form caeruleopunctata.

Small local populations (colonies) which cannot breed with other colonies due to obstruction (by mountain ranges or human development such as roads, towns and cities) may result in interbreeding within the colony. This continued interbreeding may result in specific traits becoming more pronounced. Some traits my be detrimental to a species resulting in weakness of the colony and ultimately its demise due to a poor gene pool. Other colonies may have a richer gene pool buy still display a specific trait which does not effect the viability of the colony.

The Brown Argus, Northern Brown Argus and the intermediate 'Durham Argus' (also known as the Castle Eden Dene Argus) are forms of the same species which have evolved to be slightly difference in appearance and have slightly different life cycles due to regional isolation. However, all three forms can breed together successfully as they are the same species. The Durham Argus is known as a 'Cline'.

A cline is a term used in the study of population genetics, and is described as 'a gradual change of a character or feature in a species over a geographical area, often as a result of environmental heterogeneity'.

What's sexual dimorphism?
Males and females of the same species may differ dramatically in wing coloration from each other. Such species are said to be sexually dimorphic. In many species, sexual dimorphism is not present or extremely subtle while in others, it may only be an obvious but consistent difference in wing coloration and pattern between the sexes of the same species.

The Orange-tip has one of the most obvious examples of sexual dimorphism. The males, have orange-tips to their wings, this coloration being completely absent in the females (see photos right).

A male orange-tipped Orange-tipAbove: A male orange-tipped Orange-tip A female Orange-tip lacks the orange.Above: A female Orange-tip lacks the orange

What are androconica?
Males butterflies may only vary in wing pattern in the area known as the androconica or sex brand. These patches consist of specialised wing scales from which sexual pheromones are released in order to attract a female.

In many species, the sex brand of the male is not visible although other wing variations may allow the individual to be sexed easily. However, in some species such as the Gatekeeper (see photos right), the male sex brands on the upper forewings are clearly visible.

Androconica visible on the male forewings
Androconica visible on the male forewings
Androconica absent on female forewings
Androconica absent on female forewings

Old age
Variation may also occur over a butterflies life span. Young, freshly emerged butterflies tend to have a rich coloration and undamaged wings while old specimens may have damaged wings and their colours may have faded. This is generally due to the loss of surface scales on the wings.

A very tired Comma
Silver-washed Fritillary
Silver-washed Fritillary in old age