Any Westbury Society News

Butterfly of the Week 27th May 2020


Small tortoiseshell: This familiar butterfly hibernates as an adult in September or October in sheltered places in woodlands and woodpiles or in our garages, barns, lofts, and church rooves, where its dark shape, with antennae folded back, can be a familiar sight. On sunny days in January or February they may wake and fly for a short while but soon return to hibernation. In March, as it warms up, they leave hibernation and seek mates and suitable patches of nettles. They are quite fussy about the choice of location and the growth stage of nettle patches. These butterflies are strong fliers and may travel a 100 or more miles in their lifetime. Many are somewhat migratory in that the spring and early summer adults fly generally NNW and the second generation from mid-August fly approximately SSE. There are influxes from the continent each year, but it is believed that most small tortoiseshells are ‘homegrown’ unlike red admirals and painted ladies. After mating the female lays several batches of 60-100 eggs on the undersides of young nettle leaves. The caterpillars hatch quite soon and feed communally and build a somewhat protective web. Once that bit of nettle is eaten out the larvae will move on and spin a new web. When ready to pupate, they will wander away from the nettle patch or find a suitably sheltered spot within it, to form their suspended pupae. In less than a month adult butterflies emerge – which is happening here and now at the end of May! Most in our part of the world go on to find mates and lay eggs which will become the second generation. These are the butterflies we see on our Buddleia and Michaelmas daisies in the autumn. They are feeding up on nectar before finding hibernation sites in September or October to pass the winter. A few of this first generation may go straight into an early hibernation as they would nearly all do in Scotland. Small tortoiseshells are nowhere near as abundant as they used to be, particularly in the south of England. The reasons for this are rather unclear but climate change may have favoured a tachinid fly that lays its eggs on the nettle leaves that get eaten by young caterpillars. These eggs then hatch inside the caterpillar and eat it out from the inside without killing it until the fly’s development is complete when it leaves the dead caterpillar to form its own pupa, from which comes a new fly. Other circumstances, like the summer drought of 2018, have meant there were few suitable nettles for this first generation to lay eggs on in June to provide the second generation that are the autumn butterflies that will go into hibernation. If the season becomes really advanced many may try for a third generation which fails completely because suitable nettles and nectar sources are not available. The factors affecting how many small tortoiseshells there are in our gardens, and in the wider countryside, from year to year, are clearly complicated.

Photos: Mick Fletcher, John Ball, Peter Bright

Cream-spotted tiger moth

A local, mostly southern species that usually flies at night but, as in this case, can be diurnal immediately after emergence. Second year running in our garden.

Butterfly of the Week 20th May 2020


Red Admiral: This spectacular butterfly probably got its name from the ‘royal navy ensign colours’ of its wings rather than being a corruption of ‘admirable’ which it also undoubtedly is! It is a butterfly which traditionally did not survive British winters and so our butterflies came in several waves of immigration – first from North Africa and Southern Europe, then from Spain and Portugal and lastly from Eastern Europe. The offspring of the butterflies that came to the UK do, to some extent, head back south again. The variable numbers of this butterfly in the UK each year reflects the size of these several immigrations. With milder winters it may be that there will be some homegrown butterflies as they can be seen flying in any month of the year. Unlike Peacocks and Small Tortoiseshells, they do not go into proper winter torpor for hibernation. It maybe that caterpillars and pupae can also survive our winters in increasing numbers, which provide some of the early butterflies seen in March and April. The main food plant is stinging nettle and eggs are laid singly on the top surfaces of suitable nettle leaves. The caterpillar constructs a tent out of the leaf so remains hidden for its whole life. New tents are made as it grows and finally forms the pupa inside a tent made from a folded nettle leaf. Do try looking for them on nettles. There are no distinct generations with so many immigrants coming in widely variable numbers throughout the summer, but all the life stages can be found in most months of the year. In autumn they can be seen feeding up on the sugars in ivy flowers or rotting fruits before heading south. There is considerable interest in just how much they are now overwintering in the UK successfully, so records in December and January would be particularly interesting.

Photos   John Ball    Robert Maxwell Wood

Butterfly of the Week 13th May 2020



Brimstone: That this butterfly is the origin of the word ‘butter-fly’ with its abundance and colour, flying early in the year, is a lovely story. Brimstones over-winter as adults in woodland and hedgerow places such as amongst ivy. They can appear at any time in January or February flying on warm sunny days but will inevitably return to hibernation. They emerge properly in late March and April and will wander widely in search of mates, and for the females, in search of purging buckthorn around Westbury and alder buckthorn in parts of the country with more acidic soils. The males are bright yellow and unmistakeable, while the females are a much paler greenish cream colour – resembling large whites in colour and size. However, once they settle, with wings always closed, the lack of black wingtips and the pointed shape of the wings make them easy to recognise. Having found a suitable buckthorn shrub, the female will flutter around until exactly the right places have been found and then lay one egg in each of them. These eggs hatch to produce a green caterpillar which can be found quite easily by looking closely at the leaves of a buckthorn bush. The pupa is formed on the underside of a leaf and has the appearance of a folded leaf. By the end of June the adults that flew in April and May will have died and during July and August the new generation of adults will have emerged from their pupae and will be feeding up on nectar from flowers, often purple or blue, such as knapweed and buddleia, before going into hibernation for the winter. There is just this one generation a year.

Photos Peter Bright

Azure blue damselfly

Another species to emerge this month, the Azure Blue damselfly is more often met with in garden ponds than the Common Blue, which prefers large ponds and lakes. Not easy to distinguish, but the Azure Blue has blue shoulder stripes narrower than the black lines below them, unlike the Common Blue. This is a male, the females are usually more greenish on the back.

Butterflies of the Week 6th May 2020



Large and Small whites:  These are the ‘Cabbage Whites’ that are a gardeners’ nightmare. There are two separate species the Large and the Small. They both over-winter as pupae formed at the end of August or beginning of September and emerge in April the following Spring.

The Large White lays eggs in batches, particularly on the leaves of domestic Brassicas, up to 150 at a time. They hatch into caterpillars that feed particularly on the outer leaves of ‘cabbages’ and, being so exposed, their bold black and yellow colouring indicates to predators their unpalatability. There is some help for gardener’s in the form of the ichneumon wasp, Cotesia glomerata. These wasps lay between 15 and 80 eggs into young large white caterpillars. These wasp larvae feed on the caterpillar’s fat reserves without killing it and finally, when fully grown, break out of the now dead caterpillar forming a collection of yellow cocoons around the corpse.

The Small White lays its eggs singly and the caterpillars move onto the underside of leaves in the heart of the plant doing considerable damage. Being green in colour and being on the underneath of leaves makes them well camouflaged. In the same way as for the large white there are a variety of parasitic wasps (including Cotesia rubecula) that lay eggs inside young caterpillars.

To tell these whites apart look at the front edge of the forewings. In the Large White it goes all the way around the point of the wing as unbroken black. In the Small White the black is almost entirely on the front edge of the wing. Large White females and males and females of Small Whites have two more or less conspicuous black spots on the upper surface of the forewing. Male Large Whites have no such spots. Generally, the Large Whites are distinctly larger than the Small Whites, but they can each vary being extra small or large in size. You might think of Large Whites as being Peacock sized and Small Whites as being Small Tortoiseshell sized.

For both these Whites there are 2 generations each year with the butterflies flying in April and May laying eggs that become the butterflies flying in July and August whose eggs will go on to produce the overwintering pupae.

Photos   Peter Bright   Mick Fletcher


Broad-bodied chaser

Male broad-bodied chaser (females are brown), the second of our damsel & dragonflies to appear in spring. Males patrol ponds and aggressively chase way other males that appear.

Weather data for March and April 2005 to 2020. Lynch Lane, Westbury-sub-Mendip

2020.4.5 March max min rain data 2006 to 2020

2020.4.30 April max min rain data 2006 to 2020

Westbury Butterfly of the Week 29th April 2020


Green-veined white: It looks like a cabbage white but isn’t. They over winter as pupae which emerge in April and lay their eggs on wild relatives of cabbages – garlic mustard, charlock, lady’s smock and other wild brassicas. In gardens they may use nasturtiums and Alyssums. The offspring of the butterflies flying now emerge in July or August and their offspring, in turn, will become the overwintering pupae. The butterfly is the size of a small white but on the upper side of the forewings the black on the wing tip goes round the point of the wing. In the small white it is only on the front edge. The underside of the hind wing has veins heavily dusted with black and yellow scales giving the ‘green veins’ in its name. Compared to the ‘cabbage whites’ both large and small, they are much more commonly seen out in the wider countryside though they do pass through gardens on their wanderings. The whites seen on the top of Mendip are more LIKELY to be green-veined whites whereas in your garden cabbage patch, it is the other way round. See Butterflies of the Week for 6th May.

Photos John Ball   Peter Bright

Butterfly of the Week 22nd April 2020


Holly blue: This little piece of flying sky is a butterfly of woods, hedgerows and gardens. The female has broad black borders to the wings, while those of the male are clear blue and resemble the common blue. It can be distinguished by the silver with small black spots undersides of the wings whereas the common blue has the underside brown with black and orange spotting. More useful is that the holly blue, being a butterfly of trees and bushes, flies much higher than the common blue that is a butterfly of meadows and stays close to the ground – usually!    The holly blue is unusual in having two generations a year where the caterpillars of each generation have different food plants. The adults flying now, in the Spring, have emerged from pupae that have overwintered. After mating the females lay eggs on the flower buds of holly. The caterpillars will eat the flower buds and such damage can be seen. After two or three weeks as a pupa hidden in leaf litter the adults emerge. This generation emerges in July and lays eggs in the flower buds of ivy. It is the pupae from these caterpillars that will over winter. This butterfly should, really, be called the holly and the ivy blue!

Photos  Robert Maxwell Wood