Violets – 7th September 2009
The Forestry Commission Scotland has now added two butterflies to its forestry strategy and they join a list of other plants and animals. One of the butterflies is the pearl-bordered fritillary that is in trouble in many parts of Britain. This attractive woodland butterfly has become extinct in some counties in England since 1997 and may well be heading that way in Wales. In the Highlands the situation is unclear but the latest distribution maps show that a number of colonies have been lost in the east of the area since the surveys of 1980 to 1994. What the Forestry Commission will be doing is to positively manage areas of woodland for the butterflies. To assess how this can be done is to look at the requirements of the butterflies. To start with they need a food plant for the caterpillars and in the case of this fritillary it is mainly common dog violet, heath dog violet and, less commonly, the marsh violet.
The common and marsh violets are common throughout the Highlands with the marsh violet, as the name suggests, being found in wetter areas. The photograph is of common dog violet taken on a wall on the edge of birch woodland near Inverness. The heath dog violet is scattered in various parts and is absent from large areas. Then there is the food requirements of the adult butterflies and these are limited as it is the spring flowers they go for as a nectar source. At one time this butterfly was known as the April fritillary as it flew that early in the year. Then many years ago the calendar was put back by 11 days so it now flies in May and is on the wing now and up until very early in July. So the nectar sources are mainly early spring flowers such as bugle, dandelion, birds-foot trefoil and bluebell.
The nectar source and the food plants of the caterpillars may be present but they have to be in the right sort of conditions. This means that they have to be in sunlight and in sheltered situations. In the past this was achieved by common and widespread forestry practices that led to an abundance of woodland butterflies. Coppicing, mainly hazel to make sheep hurdles, and fencing, created glades where the spring flowers flourished and they were warm and sheltered. The same could be achieved by regular felling on fairly short cycles. Woodland rides were wide for access and these were sunny and sheltered. Such woodland practices have died out in many areas especially where conifer plantations took over.
All these aspects will have to be implemented and there is one addition that was not found in the old woodlands. Undulating margins in glades, rides and woodland margins can give small areas where the plants are present and at some time during a day the sunshine comes in and it is sheltered from the wind. Another important aspect is that where colonies occur there would ideally be “corridors” of suitable habitat so that there can be an exchange of butterflies from one colony to another. Once the females have laid their pale yellow eggs on the violet leaves it is just the start of a cycle fraught with problems such as predation. The caterpillars feed intermittently on dense flushes of violet seedlings or fresh leaves of older plants. During the winter the caterpillars hibernate in curled up leaves and then start feeding again in March before pupating under the leaves of the violets or on nearby plants. Where the appropriate management is implemented regular transect counts can be made to assess the success or otherwise.