Friday, 25 August 2006

Rare caterpillar found at Holkham

The National Nature Reserve at Holkham is an excellent place to visit in search of wildlife. The combination of habitats (such as dunes, inter-tidal sands, grazing marsh and pine woodland) allows the development of many very different communities of animals and plants. During the winter months, visiting shore larks and snow buntings can be seen on the saltings, while huge flocks of geese crowd onto the grazing marsh. The summer warmth brings natterjack toads, spotted flycatchers and a whole host of buzzing, chirring and clicking insects. The heat also attracts the tourists and Lady Anne’s Drive soon hosts two long lines of parked cars, the sun on their windscreens creating the illusion of two great glasshouses stretching out towards the pines. Fortunately, Holkham is a large site and, with the lure of the sea, it is very easy to leave the crowds behind and lose yourself in the solitude that the reserve has to offer.

Bedstraw Hawk-moth, Holkham

Just the other weekend I visited Holkham with two friends whom I had not seen in a long while. It was the perfect venue for a gentle walk and provided an ideal opportunity to catch up on each other’s news. Skirting west alongside the landward edge of the pines, we soon reached the George Washington Hide and followed the boardwalk out onto the dunes. Common blue butterflies were on the wing in the shelter that the dunes provided, and alongside these were graylings, dark green fritillaries and dozens of gatekeepers. Scanning the ground for beetles and other invertebrates soon turned up our most interesting find of the day – a bedstraw hawkmoth caterpillar. This pale, straw-coloured caterpillar was a sizeable beast – the length and thickness of your middle finger. Complete with a series of ‘eye-spots’ along the flank and a red ‘horn’ on the rear end, I recognised it as a hawkmoth caterpillar, but one that I had not seen before. Photographs were duly taken and, once home, these were compared with various illustrations before my tentative identification was confirmed by a number of experts.

The bedstraw hawkmoth is a migrant species, albeit a fairly regular one, and so was not something that I would necessarily have expected to encounter as a caterpillar. Most records tend to come from the eastern counties and, in particular, from coastal localities. Adults usually occur between May and August and may be taken at light traps but the caterpillars themselves tend to be found from July to September. They feed on various bedstraws and willowherbs before overwintering just below the surface of the soil. At various times in the past, temporary populations of this moth have become established in North Norfolk. This latest record may suggest that one such population exists today at Holkham.

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