Tuesday, 30 August 2016

Variation and form ...

Common Blue (Polyommatus icarus)

Surely one of our most beautiful insects ...





P. icarus is the most widespread member of the Polyommatinae found in the British Isles but has significantly declined with the destruction of much semi-natural herb-rich grassland through agricultural intensification. It now lives in discrete colonies on remaining herb-rich grassland and disturbed sites where its larval foodplants can be found. The primary foodplant is Bird's-foot Trefoil (Lotus corniculatus). Black Medick (Medicago lupulina), Common Rest-harrow (Ononis repens), Greater Bird’s-foot Trefoil (Lotus pedunculatus), Lesser Trefoil (Trifolium dubium) and White Clover (Trifolium repens) are also used.

Two broods are typical in the southern counties of England and one brood further north. Occasionally, in favourable seasons, there may be a third brood. In good years, adults may be seen as early as the middle of May on more southerly sites. These peak at the end of May, giving rise to a second generation that emerges in the second half of July, peaking in the middle of August. Colonies in northern England and Scotland typically have a single brood that emerges in June, reaching its peak in July. I am currently seeing freshly emerged individuals of both sexes in local Surrey and Sussex locations. Whilst the male has bright blue uppersides, the female is primarily brown, with an extremely variable amount of blue and extent of spotting. Not only can this be noted in distinct geographical populations but also within the same seasonal population. P. icarus is therefore the subject of a vast number of named and unnamed aberrations. The brown form of the female is sometimes mistaken for the Brown Argus (Aricia agestis) and vice versa.

The above images, in descending order, show (i) a male from 2015, (ii and iii) two females from 2016, and (iv) an extremely blue female referable to ab. supra-caerulea, Oberthür (1896) from St Mary’s, Isles of Scilly, 2012.

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Sunday, 14 August 2016

A matter of perception ...

Meadow Pipit (Anthus pratensis)




Often overlooked due its unfortunate reputation for being an uninteresting species, A. pratensis is one of the most widespread and ubiquitous of all UK species. However, flocks of migrant A. pratensis are always worthy of closer scrutiny since they can be a good carrier for wagtails and rarer pipit species.

In spring, A. pratensis arrives back in Sussex to breed and many more pass through heading further north. Passage can begin in late February, but March and, to an extent, April are the key months. Although some birds may remain in Britain to overwinter, in autumn, most British birds head south, with many passing through Sussex on the way. Autumnal movements gain momentum in September through October and are often very evident at coastal sites with birds moving along the coast. Confusingly, such movements can be eastwards or westwards but the latter generally predominate and are often into the prevailing wind.

Throughout Sussex it is a bird of open, extensive rough and grassy habitats, from sand dunes and salt marshes to wet grassland, heaths and unimproved chalk grassland, where it feeds and nests on the ground. Take more attention next time you see one and appreciate the fact that it is common …

References:

Scott-Ham, M. (1996). Meadow Pipit. Birds of Sussex. Sussex Ornithological Society, pp. 398-399.
Scott-Ham, M. (2014). Meadow Pipit. The Birds of Sussex. Thetford: British Trust for Ornithology (BTO) Books on behalf of the Sussex Ornithological Society, pp. 542-543.

Wednesday, 3 August 2016

The sleeper ...

Small Tortoiseshell (Aglais urticae)

Chiddingfold Forest, 2016



The beautiful Small Tortoiseshell A. urticae can turn up almost anywhere and appears in gardens throughout the British Isles. It is one of our most successful butterflies. As its scientific name correctly suggests, it is most-often seen where nettles grow in abundance; both Common Nettle (Urtica dioica) and Small Nettle (U. urens) are used for egg-laying and larval nutrition. A. urticae is also frequently encountered whilst hibernating in an outbuilding, such as a garage, shed or barn, where they may be found in the company of other individuals. Further hibernation sites include hollow trees and woodpiles. I personally experienced some fifteen individuals overwintering in an old converted tractor shed last year. They were surprisingly first seen to be entering hibernation on 31st July 2015. They stayed in this state for eight months and only occasionally showed signs of any movement.

The adult butterflies can be seen on the wing at any time of the year, even on the last days of December or first days of January if the temperature is high enough to wake them from their dormancy. However, adults normally emerge from hibernation at the end of March and start of April. There are typically two broods each year, except in the north, where there is usually only a single brood. Whether single or double-brooded, the butterfly can be a familiar sight in late summer as it imbibes nectar to build up essential fats in preparation for its period of rest.

The above images show two separate males, the first, exhibiting dorsal thermoregulation on a forestry track in early July, the second, having successfully overwintered in the adult form, resting on a log pile in early April; the antennae tucked tightly between its forewings and showing the exquisite camouflage of the underside.

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Monday, 1 August 2016

15th August 1832 …

Lulworth Skipper (Thymelicus acteon)






To the lepidopterist the name James Charles Dale (1791-1872) will always be associated with the discovery of a butterfly new to Britain, Thymelicus acteon, the Lulworth Skipper. It is recorded, that on the 15th August 1832, Dale, having journeyed around twenty miles on horseback from his home at Glanvilles Wootton, reached Durdle Door, near Lulworth Cove. Here he found considerable numbers of acteon along the cliff tops. However, it was not until John Curtis reported Dale’s discovery in Volume 10 of his British Entomology, published in 1833, and named it the Lulworth Skipper, that the discovery was announced in print.

The female (pictured above) is quite recognisable from the pale orange crescent on her forewings, which is either lacking or very feint in the male. The male is generally darker in colour and has a distinctive sex brand on its forewings. As its name suggests, the distribution of this species is centred around Lulworth in Dorset, between Weymouth and the Isle of Purbeck. Colonies are most often encountered on south-facing, sheltered slopes, on chalk or limestone grassland, where tall patches of Tor-grass (Brachypodium pinnatum), its larval foodplant, can be found. In Britain, this species is at the northern limit of its range and is rarely found more than 5 miles from the coast.

The above images, in descending order, show (i and ii) a female on its larval foodplant, (iii) a freshly laid batch of eight eggs in the dried stem of B. pinnatum, (iv) typical acteon habitat overlooking Lulworth Cove with B. pinnatum in the foreground and (v) the view looking towards the northwest from its home on Bindon Hill.

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