News from the Riverside – August 2019:
Everyone will recall the intensity of last summer’s heat. Fortunately we have only had a brief repeat of that for the moment although inevitably such summers will occur more frequently with climate change.
For wildlife the heat and drought conditions of last summer were a mixed blessing but many species of butterfly responded by producing good populations not seen for very many years. They are so very dependent on weather and are able to respond very quickly when suitable conditions arise.
Significantly, because last year was by and large favourable for butterflies, this year there have been good numbers too taking advantage of a reasonably warm, dry and sunny summer. Indeed starting in the spring it was clear that we might be in for a good year. Butterflies delight the eye as they move about from flower to flower in our gardens and out in the wider countryside.
Out on the Sudbury Common Lands management of thistles is very important. Some species can be very invasive so these are controlled but other species do not overwhelm the grasslands and so they have a role to play in encouraging wildlife. Species such as nodding and welted thistle prefer dryer and poorer ground where grass growth provides less feed for the cattle. On wetter ground the statuesque spires of marsh thistle can be dominant. While they are all in flower they are attractive to an enormous range of insects including butterflies which are attracted to the ample source of nectar. Once flowering is finished charms of goldfinches then feed on the thistle seed heads through the summer and autumn.
This year all through July there have been very large numbers of meadow browns, as well as small tortoiseshell butterflies on the thistles but it is the painted lady that really fascinates. These large and colourful, if somewhat faded and tatty travellers cover vast distances to reach our thistle beds. In some years very few reach our shores but occasionally they are plentiful and that is all down to the weather. They feed busily before egg laying on thistles and, weather permitting, producing a new and pristine generation about a month later.
The painted lady butterfly is the most widespread butterfly on the planet but where do these summer visitors come from? If rains are plentiful and vegetation prolific in North Africa the first generation completes its life cycle and as summer begins the butterflies head towards Europe. They are very strong fliers but only travel so far as their lives are short. The butterflies destined for our shores originate from eggs laid in Northern Spain and, in most summers, the new generation reaches our shores in varying numbers. This year there have been plenty of these fast flying ladies on wing although it may still be some years before we see a repeat of 1996 when they arrived in their millions.
Our native butterflies survive the English winters as eggs, caterpillars, pupae or as hibernating adults but until recently it was assumed that all painted lady butterflies died when our chilly autumn weather arrives. Recent research, however, has discovered that many of these butterflies rise high into the sky and head south. The painted lady is truly an opportunistic traveller seeking out suitable feeding and breeding grounds depending on the weather conditions.
Adrian Walters (Clerk to the Trustees of the Sudbury Common Lands Charity and Ranger)