It is the end of September, there are fewer butterflies on the wing, yet on my walk today I am accompanied by a Clouded Yellow. It is one of our migrant butterflies coming all the way to our shores from North Africa and Southern Europe, and can be seen almost anywhere in Britain feeding on clovers and common birds-foot trefoil.
Here in Dorset, they mostly frequent chalk downlands where they mate and lay their eggs. In late summer their numbers increase as the new British-born butterflies mingle with the succession of newcomers. Unable to survive our cold, damp winters it is still unclear whether the new generations of Clouded Yellows born over the summer return home like other migrant butterflies such as Painted Ladies and Red Admirals.
Looking at their fine features and paper-thin wings, it is hard to imagine how such a beautiful, delicate creature can navigate such large distances and be at the mercy of the elements. Winged migrations are indeed one of nature’s miracles – I wonder what tiny compass guides these fragile beings over land and sea, and what innate determination resides in their DNA, for there is no opportunity for them to learn from older experienced individuals.

Research suggests that butterflies use the shortening or lengthening of the day as a cue to their travels. The caterpillars that grow when the days are lengthening become adults who fly north, but those born when the days are shortening know they need to fly south to find a food source for their own offspring. Although difficult for science to determine, butterflies seem to use the sun’s position to orientate them but at night, just like birds, it is thought they switch to using the earth’s magnetic field.

The theory is that birds, butterflies and even migratory fish have nanoscopic cells that produce a substance called magnetite in their beaks, antennae or noses. Whatever they have, their navigation is so precise it allows them to return to the same area, or even nest site, year after year with a skill and an intelligence we find difficult to fathom.
Walking home, I wonder whether we also have a hidden desire to migrate to warmer climes, or to where the living is easier. There is an autumnal chill in the air and the nights are rapidly drawing in – how nice it would be to head south too.
Passing the church my eyes are drawn skywards, and there, circling above the tower, is a lone swift. Feeding on insects, and sleeping on the wing, swifts begin their journey to central Africa in mid-July before the night air becomes too cool for their food source. This young swift is late to leave and far behind his flock. I wish him luck on his long journey and look forward to the day when I am in the warm sunshine watching him circle above our church tower once again.
n Dr Susie Curtin (email curtin.susanna@gmail.com)