Buddleia bushes
are flowering in our garden and I love their rich scent. It’s not only me that
is attracted to the plants, as their dark purple flower spikes are visited by large
numbers of bees and butterflies that collect the supplies of nectar provided by
the plants. The Buddleia benefits, as
pollen is spread by the insects when they gather this “gift”, and the bees and
butterflies gain fuel for flight and a high-energy source of food for rearing
young in bees. Both groups of insects also use the sugars in nectar as a store;
with bees producing honey and butterflies body fat.
As the insects move over the flower spikes, it is easy to look at them closely and the common Peacock and White butterflies have been joined by Commas (Polygonia c-album), which seem plentiful this year. The wings of Commas have a jagged profile and, as with most butterflies, have beautiful colouration on the upper surface of the wings and a brown colour on the under surface, with a pattern resembling bark or lichen. The ragged outline of the wings, and the patterns of their lower surface, are likely to provide protection against predation during rest, when the wings are closed. The butterflies are then camouflaged and look to me like pieces of bark or dead leaves. I say “look to me”, as our perceptions are so much governed by our own senses and we do not know how the butterflies look to their natural predators. We know that the Comma is eaten by birds like great tits,1 but presumably in greater numbers when the wings are open and the butterflies active.
A feature of the camouflage of the under surface of the
wings is the “comma” from which these butterflies gain their common name. The
marking varies from species to species, and also within species, but it is a
feature of Comma butterflies throughout the Northern Hemisphere. Why do they
have this marking? A creationist might argue that it is something for which only God
has the answer and, without wanting to sound
facetious, creationists may also feel that God created the comma as a talking
point and as a means of showing us His omnipotence. An evolutionist would have
no difficulty pointing to the selection of mutations that provide the effective
camouflage of the under surface of the wings, as the colouration presumably
enhances the survival of individuals in which it occurred. The mutations require changes in the
pigmentation of individual scales and also of the wing outline, but what were
the stages that led to the forms we see today? Does the comma provide any selective
advantage, or is it neutral? No-one knows the answers to these questions, nor
do we know why the upper surfaces of the wings have their characteristic
brightly-coloured patterns. Unfortunately, we are hampered in our inquiry by viewing Nature
with human sense organs and from a human perspective. Of course, it’s the only
approach we have and that is always worth keeping in mind, especially as humans
are so recent in the history of living organisms.
1 Nylin et al. (2001) Journal of the Lepidopterists' Society 55: 69-73
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