A Trio of Westbury Butterflies of the Week 8th July 2020.


Comma:  This is really a woodland butterfly that has had times in the past when it became quite rare.  However, since the 1960s it has increased dramatically in numbers and has spread northwards reaching Scotland in 2000.  It is now a familiar butterfly of woodland edges, hedgerows and gardens.  The butterfly is named for the white mark on the underside of the hind wing though on the other wing it will resemble a C which is part of its scientific name, Polygonia c-album.  The adult butterfly overwinters, presumably in sheltered places in its woodland habitat but not in our garages and outhouses.  On emerging from hibernation in late March or early April the males take up territories investigating any passing butterfly looking for females.  Pairing is believed to take place high in the woodland canopy after which the female prospects for suitably sunny but sheltered food plant.  In the past a much used foodplant was hop but now the main food plant is nettle but it has been found on a variety of plants such as currants, elms and willows.  The caterpillar feeds inconspicuously on the underside of the leaves of its food plant but by the time it reaches the last, 5th instar, its colouring has been transformed such that it now camouflaged looking like a white bird dropping.  The pupa is formed hanging amongst the vegetation of its food plant.  The adults of the next generation emerge in late May or early June.  These come in two forms – the normal darker form and a much paler form, hutchisonii.  The normal form feeds up on nectar and goes into hibernation in August.  The paler, hutchinsonii, mate and lay eggs that go through their caterpillar and pupal stages emerging in late August and September as a second generation.  These are the late season butterflies which will then, themselves, go into hibernation in late September or October.  There is, therefore, a mixture of one and two generations in its life cycle.

Photos   Robert Maxwell Wood    Peter Bright

Silver-washed Fritillary:   This magnificent, bright orange insect is close to the largest British butterfly and is certainly the largest in Somerset now.  This colouring is also why in some parts of the world this group of butterflies are called leopards. It is a butterfly of woodlands that have an abundance of violets growing around the moss-covered bases of trees, particularly oak.  Woods that are coppiced or thinned have an abundance of bramble, a favourite nectar source, as well as encouraging a good growth of violets. 

They spend a lot of time high in the canopy and feed on the abundance of honey dew on the leaf surfaces.  In some years these strong flying butterflies come into gardens using plants like Hebe and Buddleia as convenient nectar sources. The adults emerge in late June or July and may continue to fly into the middle of August.  They are fast and powerful fliers and the males patrol the woodland rides and canopy investigating any orange butterfly checking for virgin females.

If such a female is found there is a spectacular courtship flight with the male showering the female with pheromones from the sex brands on the front wings that show as dark lines along the middle two veins.  Following this the female seeks out patches of violets but having found them, then goes to a nearby mossy covered oak trunk base where she lays eggs, singly, in mossy crevices.  There is a fabulous colour variation of the females which is a deep bronze green colour called valesina.

It is possible that this dark colouration is favoured in poor summers as the butterfly warms up more quickly, but it is at a disadvantage in normal summers as the males take longer to find these unusually coloured females.  The newly emerged 1st instar caterpillar eats its way out of the egg and immediately hides itself in a bark crevice where it passes the winter.  This could be why ash and beech woods are unsuitable lacking the appropriate moss filled bark crevices.  From early April the young caterpillar comes down to the woodland floor and feeds on the nearby violets.  When fully grown the caterpillar goes up a nearby plant to pupate a metre or two off the ground.  The next generation of adults emerge in late June providing another spectacle of summer in Mendip woodlands.

Photos    Peter Bright


 Dark green Fritillary:     This is typically a butterfly of windswept limestone grasslands but is also found on bracken covered hillsides, grassy dunes and a variety of similar habitats.  It is named for the green wash on the underside of the hind wings.  They need the sward to be of medium height so that heavy grazing, or complete lack of such, can make the violets that are its caterpillar food plant unsuitable.  It should be much more widespread across the Mendip scarp than it is but, it is doing well at Ubley Warren.   Single individuals have been seen on the Beacon and even in a Westbury garden over the last few years. 

With suitable grazing and clearing of gorse there is hope that the butterfly will return to the Beacon once again.  The adults emerge in June and will fly for much of July and perhaps into early August.  They fly strongly and can cope with their windy habitat and have a special fondness for purple flowers like knapweed as nectar sources.  The males will patrol large areas searching for virgin females investigating any suitably coloured butterflies.  After mating, the females will hide while their eggs mature and will then search out the violets growing in suitable places before laying near to them.  As with the Silver-washed Fritillary, the newly hatched caterpillar immediately finds a hiding place in which to hibernate.  Towards the end of March in the following year the caterpillar emerges from hibernation and seeks out violets on which to feed.  The later instar caterpillars are particularly black and spiky and may be seen travelling across open spaces seeking new supplies of violets. 

The blackness presumably enables the caterpillar to warm up quickly in its otherwise exposed and cool habitat. In a very tall grass sward it may, therefore, not be able to warm up quickly enough to survive.  In the middle of May or beginning of June the caterpillars will find hidden places to pupate and the adults will start emerging again from the middle of June.

Photos   John Ball    Peter Bright  Georgina Shuckburgh

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