July 2009 – Like fungi, insects in general suffer from poor PR – butterflies are a notable exception…
After two or three disastrous breeding seasons, butterflies are fortunately beginning to appear in large numbers again. Thanks to their brightly coloured wings and nectar diet, these are one of the few popular insects families.
As they flit from bush to bush, one might have thought their movements were random, but recent technological advances have made radar tracking possible and the results have astounded the experts. Until five years ago it was assumed butterflies flitted relatively casually around the countryside, apparently moving randomly from flower to flower. When the BBSRC researchers began to track adult peacock and small tortoiseshell butterflies, they discovered a far more complex picture. Far from engaging in relatively random flights between flowers, many were clearly undertaking fast directed flights to potential feeding sites. Others mixed foraging with wider circling flights that appear to help them get their bearings.
Experts have known for years that many butterflies follow complex migratory movements, but it still comes as a surprise to most people that a creature as small as a butterfly can travel huge distances. Painted ladies, for example, cannot survive our winter and fly here from southern Europe every spring, while red admirals are blown in accidentally from France to breed prolifically in our nettles, only for their over-wintering larvae to be wiped out by January frosts.
Most of a butterfly’s life is spent as a caterpillar or chrysalis. Adults are quite short lived, but this is the critical point at which they can move relatively big distances – the problem is until now we haven’t been able to keep tabs on where they go or how they move. This is particularly important with rare species because if they are restricted to movements along hedgerow ‘corridors’ then each time a small, geographically-isolated population is lost, it may mean it is for good. On the other hand if they are they happy to move across open country the prospects for recolonising suitable habitat are promising.
The new tracking research is also exciting because it helps us plot global warming. Butterflies are at the edge of their range in Britain where many species struggle with uncertain damp, cool, summers and frosty winters. The run of recent warm, dry, summers in the 1990s and the first few years of this century saw ranges expand markedly. The speckled wood, for instance, used to be quite rare and confined to the south east, but is now found as far north as Scotland. Orange tips and marbled whites are currently experiencing similar expansions. At the turn of the last century they were almost unheard of in Wales and the Pennines. Now they are relatively common across the southern half of the Principality and are knocking on the door of Northumberland.