Forest Diary - Butterflies Get A Boost

Forest Diary, A boost for butterflies 

"In my opinion there is no better symbol of summer’s arrival than the delicate beauty of the butterfly, as it feeds on the forest’s array of wild flowers.

However, this year’s unwelcome spring weather has seen butterfly numbers drop substantially – with one of the UK’s rarest butterflies, the pearl-bordered fritillary butterfly, worst affected. In fact, if it weren’t for the Forestry Commission’s ongoing conservation work near Brockenhurst, we could easily have seen the last of them in the New Forest.

For the past decade, we have been committed to give the delicate insects a helping hand, as part of our continuing forest management programme across the region. Our team of keepers, foresters and volunteers has been busy creating suitable open habitats, by coppicing and opening up woodland ride edges, to boost the numbers of the threatened species.

However, this year’s weather has had a devastating effect on the small population. The year started too dry which had the effect of decimating the little violet plants that were providing a rich food source for caterpillars. This was then followed by intense rain which flooded many roadside drains, washing out the caterpillars themselves. Temperatures have also negatively impacted on development during the larval stages.

Thankfully, last year’s preferred weather conditions – combined with our conservation work – enabled the adult butterflies to lay eggs in new areas that had become suitable habitats for breeding. It is this growth, twelve months ago, that has ensured the rare butterfly can survive the current adverse conditions brought about by our unpredictable British weather.

Pearl-bordered fritillaries live in woodland clearings where trees have recently been cut down or coppiced, and where there are areas of grass, bracken and open scrub. They depend on a mosaic of open areas for movement between colonies and for food.

Our work concentrates on creating a finely balanced habitat for all their needs – even ensuring there is leaf litter along the ride edges for the caterpillars to sunbathe on after feeding and to roll in to hibernate. This project is being replicated in other areas too as we are constantly planning four to five years ahead to ensure the survival and, ultimately, the growth of these precious insects.

The pearl-bordered fritillary butterfly gets its name from the series of ‘pearls’ that run along the outside edge of the underside of its hindwing. The woodland butterfly lays individual eggs in May on dead bracken or leaf litter near to grassy areas where dog-violets (the caterpillar’s main food source) are growing. After about two weeks, the larva hatches and starts to feed. It will moult four times before it then hibernates for winter. In the early spring it comes back out to feed for the final time before its pupation, followed by its emergence as an adult butterfly, flying between late April and May."

For more information visit www.forestry.gov.uk/newforest.
Jonathan Cook, Forestry Commission Keeper