Butterfly spreads its wings to new areas after milder winters

Published on 29/05/2007 01:08

ONE of the most striking butterflies in the UK is colonising new areas of Scotland, according to a survey by enthusiasts.

Butterfly Conservation Scotland invited people to report sightings of the orange-tip butterfly to see how the species was faring.

Survey results are still being analysed, but the organisation has discovered that the orange-tip has spread west and north, expanding its range into the islands of Mull and Iona as well as Lochaline, west of Fort William, Cannich in Glen Affric, and Ullapool in Ross-shire.

The butterfly has been well established in England and Ireland, but until recently was largely absent from much of north-western Scotland.

It is thought the mild winter weather has enabled more female orange-tips to survive into the spring to lay eggs and the insects have gradually increased their range.

Dr Tom Prescott, Highlands and Islands' project officer with Butterfly Conservation, said: "It's really been moving north over the last 15 to 20 years. Ten years ago when we did this survey, there were a few sightings in the central belt and around Grampian. Now it has really spread into the Highlands and has become much more common. They are not migrants, they are just slowly spreading and over the years they have just been occupying more ground."

Orange-tips will spread out across an area if they can, partly because their caterpillars like to feed on garlic mustard and cuckoo flower, but there is only really enough sustenance for one caterpillar on each plant.

"The females tend to only lay one egg on the caterpillars' food plant because there's only room for one caterpillar to feed. If a female goes there and there's already an egg there, they normally won't lay," Dr Prescott said.

If they do, he said they would risk losing their offspring to a rival: "The first egg will hatch and the caterpillar will eat the egg if it comes across it."

But this gradual movement in search of a spare nesting site is limited by the temperature.

"If it's below about 11C and it's not sunny, they are just not active. You can still find the adults but they will be resting, waiting for the sun to come out and warm up," Dr Prescott said.

"They over-winter as a pupa so it is possible more of them are surviving because the winters are a wee bit milder," he added.

There are some 34 species of butterflies in Scotland and many appear to be thriving.

The small skipper crossed the border into Scotland from England last year while the peacock and ringlet butterflies have also being "doing very well in Scotland and moving north".

The checkered skipper, which is now extinct in the UK apart from an area within about a 30-mile radius of Fort William, came out in late April, when it normally mutates in the third week of May.

More info @ www.butterfly-conservation.org

www.butterflygarden.co.uk