Trip reports
Indoor Meeting: CONSERVATION OF BUTTERFLIES AND MOTHS
paddy g
Tuesday, 16 December 2008
With increase in altitude there is a corresponding decrease in temperature. Where the temperature rise is due to global warming, some lowland species, if suitable habitat is available, can migrate upwards. But those already limited to the high tops have nowhere they can relocate to and therefore face extinction. Nothing can be done to save such vulnerable creatures.
Winter conditions are essential to the survival of some mountain species as they are adapted to an extended larval stage, spending two years as caterpillars. They have synchronised life cycles with emergence of adults every two years. An extreme case is one variety of Greenland moth which spends eighteen years at the caterpillar stage; it probably eats once annually then slowly digests that single meal during the cold summer.
The Scottish climate is very varied with the winter temperature falling well below freezing point in some areas whereas in parts of the west coast there is virtually never a frost. Such favoured areas of the Atlantic fringe are home to some very specialised moths.
The machair grasslands of the west coast support a number of different butterflies and moths that feed principally on the plants of the machair. The persistence of the machair grassland depends on gazing by the crofters' cattle and sheep. So it is a concern that the subsidies for these animals is under review as crofters may no longer be able to afford to keep them.
One west coast species has females that are flightless as they emerge wingless from the chrysalis, mate, lay eggs and die. As its range includes South Uist it is a mystery how it managed to colonise an island. When the island of Surtsey was formed near Iceland by a sub-ocean volcanic eruption, it was colonised, plants and animals reaching it by a variety of mechanisms. One theory is that female moths reached South Uist on floating vegetation.
The small blue butterfly lays its eggs on the flowers of kidney vetch on which the caterpillars feed. This butterfly requires a special habitat where open spaces allow kidney vetch to grow, but with fringing tall gasses on which the adult butterflies can roost at night.
Fifty years ago the speckled wood butterfly was found in the Inverness area. It spread along the Moray Firth then into Donside and has now reached Deeside. It frequents shady glades and rides in woodland and on the fringes of woods, areas where the sun's rays are shielded by the canopy. The Scotch Argus followed the same pattern of spread but about five years ahead. The reason for these movements may be related to availability of habitat or to climate change.
Up to five years ago the comma butterfly did not breed in Scotland. It is now spreading northwards and three have been recorded in Aberdeenshire.
Stray peacock butterfly used to be seen in Aberdeenshire but there was an incursion in 2003. As this species overwinters as an adult it may spread northwards if enough invaders arrive and then survive the winter.
In glens, some species need the habitat that results from sheep gazing as grassland specialists prefer a short sward. The ideal regime is light grazing in summer and heavier grazing in autumn. If sheep are removed, long grasses develop whilst juniper and gorse invade. Highland cattle are used extensively in conservation as they can thrive on low-grade forage and are outwintered. On upland grasslands, red deer are the important grazers.
As with birds, varied deciduous woodlands provide good mixed habitats for butterflies and moths whereas uniform conifer stands do not.
We were treated to a delightful account of lives and changing distributions of some butterflies and moths. And we learned the difference between butterflies and moths - not very much really!