Local people can expect to see 5 to 10 species of butterflies in their garden over the season if they grow appropriate flowering plants. A few visits to our Nature Reserves may allow them to double the number.
The varied scenery of Wharfedale ensures we have a reasonable range of native species, although the Northern Brown Argus is our only rarity. This small brown butterfly can be seen in June in the upper dale, where it is well established in most places where its foodplant, the Rockrose grows.
Wharfedale hosts all of the commoner migrant species from time to time, nearly every year the Red Admiral and the Painted Lady, sometimes the Clouded Yellow, and very occasionally the Camberwell Beauty.
Study of over 50 years butterfly records compiled by the Wharfedale Naturalists Society reveals a substantial increase rather than decrease in the number of species seen, perhaps due to the effects of global warming, certainly due to species such as the Comma moving North. The incomers seem to be thriving, and a steady increase in the number of colonies is typical. For some long-term residents however, such as the Common Blue, habitat loss and degradation has meant the extinction of local colonies and there is concern over the increasing isolation of the remainder.
Estimation of the size of colonies year on year is difficult and only qualitative information may be derived from our records. An earlier review looking back over 23 years by our former president Freda Draper showed two species now common, Orange Tip (prior to 1970) and Peacock, to have been markedly scarce. Brimstone and Holly Blue were also then very scarce but are now seen yearly Alder Buckthorn, the food-plant of the Brimstone, has been planted in some numbers, helping this lovely insect become a common sight on our Sun Lane nature reserve. Good counts of the incomers Small Skipper, Gatekeeper been obtained yearly, and Ringlet, virtually unknown here in the last millennium, has become abundant. In 2003 confirmation that the Speckled Wood bred in Wharfedale was obtained for the first time, and since 2006 it has become a common sight in our dales.
Year on year more sites are being found for the three elusive Hairstreaks that are resident here, Green, Purple and White-letter. The spectacular Dark Green Fritillary, long thought to have been lost from the area, is now often seen in Upper Wharfedale and is breeding on several sites.
In contrast, the Wall, designated ‘common’ in the 1979 survey, is now rarely seen. We hope this decline is merely cyclic and the insect will recover.
Since the use of transects – walks to a set pattern to estimate numbers more accurately – is well established, five have been developed by Butterfly Conservation in Wharfedale. One is part of the Wider Countryside scheme, looking at areas chosen at random throughout the country. Two monitor important Northern Brown Argus sites near Grassington.(The newest, at Kilnsey replaces an earlier transect at Skyreholnes). The remaining transect monitors the changes taking place in a reclaimed brown-field site in Burley-in-Wharfedale and is walked by the Society.