Complexity and the Comma

Species decline and expand in response to environmental pressures in ways that are complex and not always well understood. Most of us appreciate straightforward stories… a simple cause produces a well defined effect. Complex systems don’t always work that way. There are many examples of unintended consequences as a result. The introduction of predators to control pest species has a long and unfortunate history… The expansion and decline of animal and plant populations is another part of natural history where the stories are not always simple.

A beautifully camoflaged comma butterfly feasting on apples in a Manchester garden. Note the white comma shaped mark on the underwing.

Take the comma butterfly. This attractive insect was heading towards extinction in Britain in the early twentieth century. Descriptions in journals and specimens in museum collections show that it was widespread in the eighteenth and early nineteenth century. It declined in fits and starts until it was restricted to a few localities in the Welsh borderlands and southern England by the beginning of the twentieth century. Changes in land management, unusually cold winter weather and the use of pesticides were all blamed, but in truth, no-one is entirely sure why there was such a severe decline. No commas were to be seen in the Manchester area in the early twentieth century.

The beautiful bright Hutchinsonii form of ther comma butterfly is an evolutionary response to the problem of cold northern winters

There was some expansion in the second quarter of the twentieth century, which reversed in the 1950s and 1960s and then a dramatic expansion in the last quarter of the twentieth century. By the late 1980s commas were common once again in gardens and parks around Manchester. The butterfly has now expanded across most of England and can be found as far north as the Scottish borders: a remarkable reversal of fortune! The warmer winters of the late twentieth century, together with behavioural changes and adaptations are probably significant factors in the expansion, but no-one is absolutely certain which of these is most important. This is an area of research where anyone can make a contribution. The comma is an easy species to identify and records of its distribution help to draw a picture of its fluctuating fortunes!

David Green
Phil Rispin
Dmitri Logunov

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