Two Butterflies of the past month

 Small Blue: This diminutive little butterfly is, along with Grizzled Skipper and Brown Argus, Somerset’s smallest butterflies. It belongs to the Blue family though its ‘blueness’ is more steely grey in males and plain brown in the females. In flight it looks silvery from the undersides of the wings being particularly conspicuous. The only food plant is kidney vetch. This plant grows well in unimproved limestone grasslands where there is some disturbance keeping the vegetation sparse providing opportunities for the kidney vetch to spread. The butterflies need some nearby scrub for the adults to collect nectar to rest and find each other. They will happily land on people to pick up the salts on our skin. Typically, these scrubby areas are in sheltered spots at the bottom of south facing slopes while the kidney vetch grows on the much more sparsely vegetated slopes nearby. The adults usually emerge in late May or early June and can be seen basking and courting on bramble or other scrubby plants.


The females then seek out suitable kidney vetch flower heads in which to lay a single egg. The caterpillars are cannibalistic so there is benefit in egg laying females to make sure that an egg has not already been laid in a flower head as the larger caterpillar will eat any smaller ones. The larvae feed in the flower head going through 4 instars and by July are fully grown. The earliest 4th instar caterpillars may pupate and go on to produce a limited second brood in early August. However, most will seek a place to over winter presumably hidden at ground level. In the following April or May, the larva will pupate and be ready to emerge in late May or early June once again. It is not a butterfly of the Wider Countryside being confined to sites managed for the kidney vetch. There are very few colonies in Somerset, but we have two of the best at Stoke Camp and Draycott Sleights. For an unusual place try the Odd Down Park and Ride car park which apparently has a thriving colony and presumably a good growth of suitable kidney vetch.

Photos   John Ball   Peter Bright


Small pearl-bordered fritillary: Like the Small Blue this is a butterfly of Nature Reserves.  In this case they are managed for the scrubby, bracken covered somewhat moist grassland and woodland edge habitats where suitable violets grow well. On Mendip the adults emerge at the end of May and into the first two weeks of June. The males will patrol tirelessly searching for virgin females. They will visit a wide variety of flowers as nectar sources. Once mated the females will seek out suitable mats of violets growing in relatively damp and lusher areas to lay their eggs. The eggs are laid singly and not necessarily on the violet leaves but sometimes just nearby.  The caterpillars go through 5 instars but by the end of the summer in the 3rd or 4th instar they go into hibernation.   The following spring, they will continue to feed and after the 5th instar will pupate by the end of April, and will emerge in late May or early June as the fresh and beautiful butterflies they are. There are a variety of sites across Mendip where they can be seen from Crook Peak, Doleberry Warren, Shute Shelf, Ubley Warren and Priddy Mineries. They have recently disappeared from the Blackdowns in South Somerset but have strong colonies in and around Exmoor.

Photos   Peter Bright


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