The re-establishment of the large copper butterfly Lycaena dispar batava obth. on Woodwalton Fen National Nature Reserve, Cambridgeshire, England, 1969–73

Abstract

The Dutch race of the large copper butterfly ( Lycaena dispar Haw.), was introduced to Woodwalton Fen in 1927 and with careful management survived until 1969, following an exceptional July flood in 1968 which submerged the food plants, greatly reducing oviposition. This paper records the re-establishment of the butterfly in 1970 from caged stock and the population growth in the following three years in relation to weather conditions and fen management. It is suggested that the insect is not perfectly adapted to a fen environment because it has specialised requirements in terms of size and situation of the food plant. It is at risk from drowning if floods occur before or after the hibernation period and slight changes in the growth form of fen plants, which may overshade the food plant, can influence egg production. Experimental work suggests that when the fen vegetation is modified by cattle-grazing during June and July egg production increases because the food plants are made more accessible to the female butterflies. The heaviest mortality occurs in the period from oviposition to the beginning of hibernation but there is no known management technique which will reduce this. However, after emergence in the spring, protection in muslin cages significantly increases the survival rate. It is estimated that only about 30 ha of the Fen can be maintained in a suitable condition for the butterfly to breed successfully. It seems likely that this is too small an area for the insect to maintain itself without artificial aid such as protection for some of the larvae, creation of germination conditions for the food plant, continuance of a controlled grazing regime and the maintenance of a reserve stock in case re-introduction becomes necessary.