The latest report form Michael Walter
Late summer has proved an extremely uninspiring end to the butterfly season. Bread-and-butter species, such as gatekeeper, meadow brown and ringlet, appeared in only moderate numbers, but as they faded away in the second half of August the expected flush of colourful Nymphalid butterflies (peacock, red admiral, comma and the occasional small tortoiseshell) failed to materialise. However, my disappointment was tempered by two rather exciting discoveries about a month apart, and on the same stretch of ride: a single wall brown and a small heath. What is so remarkable about those two butterflies? Both were moderately common on the reserve in the 1980s, but then declined in the 1990s for reasons unknown, with my last wall brown being seen in 2000, the small heath disappearing a year earlier. Both belong to the brown family, along with meadow browns and gatekeepers, and both have caterpillars that feed on grasses, the fussier small heaths preferring the finer-leaved species. The wall brown is a sun-lover par excellence, seeking out the warmest places to stretch its wings, often resting on bare paths and, yes, walls. Its decline in the late 1980s coincided with a series of cool, wet summers, so it is possible that its disappearance was related to climate; but why has it failed to make a strong comeback during the much hotter and drier summers we have been enjoying of late? Both species seem to prefer ground that has been broken up by livestock or disturbed in some other way so that the grass sward is laced with bare soil. At Blean all the rides in the early 1980s were largely free of vegetation, a legacy of the previous owners who had rutted the rides during winter extraction of timber and then bulldozed the surface level again each summer. When the RSPB took over, a policy was instituted of keeping tractors off the rides from autumn right through to early summer. The result was a frustratingly slow recolonisation by vegetation, the infertile subsoil that had been exposed by the bulldozers being a poor medium for most plants. Gradually the wounds have healed, but this greening-up could conceivably have made the rides less attractive to these two butterflies, although the continuing presence of many bare patches suggests that this cannot be the whole story. Whatever the truth may be, the good news is that two species once considered lost forever have rediscovered Blean Woods, and it now remains to be seen if those individuals were the vanguard of a recolonisation.
An insect that I initially mistook for a small moth turned out to be a remarkably tiny speckled wood butterfly. Some species can vary considerably in size, depending on how well they’ve fed as caterpillars, but it is also likely that the extreme drought this year has affected the development of many insects.
Sweet chestnut coppice used to cover much of the reserve, but as a non-native species with rather limited value to wildlife its dominance has been drastically reduced over the past 36 years by felling stems and killing the stumps. However, recent research suggests that an infusion of chestnut leaves has the remarkable property of inhibiting Staphylococcus aureus from producing a toxin. This may all sound a bit arcane until you realise that the bacterium in question is responsible for the notorious MRSA infections that are difficult to treat with conventional antibiotics. It has not yet been possible to isolate the active compound in the leaves but, while we still may not want to see plantations of sweet chestnut on the reserve, we should be grateful that the tree may have the redeeming quality of eventually banishing the headache of MRSA from hospitals, so safeguarding vulnerable patients.
Michael Walter
michaelwalter434@gmail.com
01227 462491
Small heath on devil's bit scabious
Wall brown