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The Lulworth skipper ( Thymelicus acteon) is a butterfly of the family Hesperiidae. Its name is derived from Lulworth Cove in the county of Dorset, England, where the first specimens in Great Britain were collected in 1832 by English naturalist James Charles Dale.
The species occurs locally across Central Europe, Asia Minor and North Africa, where its population is considered stable. Its numbers have declined in Northern Europe, leading to its European status of "vulnerable". Its range in Britain is restricted to the south coast of Dorset, however it is locally abundant and its numbers currently are perhaps at their greatest since its discovery there.
With a wingspan of 24 to 28 millimetres, females being larger than males, the Lulworth skipper is a small butterfly, the smallest member of the genus Thymelicus in Europe and among the smallest butterflies in Britain. Aside from the size difference, the sexes are distinguished by females having a distinct circle of golden marks on each forewing. Due to their likeness to the rays around the eye of a Peafowl feather, these are often known as "sun-ray" markings, and they can faintly appear on males.
Variations are known to occur; in north-west Africa, the uppersides of the forewing and hindwing are darker, with hints of greenish or greyish brown. Similarly-coloured races occur in Spain, Elba, Crete, and other eastern Mediterranean islands. T. acteon christi, Endemism to the Canary Islands, displays colour variations, with the uppersides of the forewing showing defined yellow–orange markings.
The butterfly is sexually dimorphic; females have a distinct circle of golden marks on each forewing, often called "sun-ray" markings due to their likeness to the rays around the eye of a Peafowl feather. Males sometimes have these markings, though they are noticeably fainter (see Illustration 1).
In Great Britain, where the butterfly reaches the northern limit of its range, its distribution is restricted to the southern coastline of the county of Dorset. Here, both the population and range have changed little in recent decades; it is locally abundant, with the majority of colonies found on the coast between Weymouth and Swanage and on the Purbeck Ridge, a line of inland chalk hills. Two outlying colonies also exist, at Burton Bradstock and on the Isle of Portland; the cause of the colony on Portland is unknown, but has been put down to either natural colonisation or released specimens. There is evidence to suggest that the Lulworth skipper is now more abundant in Dorset than at any other time since its discovery in 1832.
Although colonies of Lulworth skippers existed in Devon, the species has, beyond single records, not be seen in the county since the 1930s. Similarly, records of occurrences exist for Cornwall, but they have not been verified as native colonies.
Habitats are primarily on unfertilised calcareous grassland; this includes chalk download, coastal grassland and undercliffs in Britain. In all of these habits Tor-grass ( Illustration 2), the butterfly's sole food plant and that on which it lays eggs, is widespread. Tall, ungrazed grass is a favoured habitat due to oviposition and larval development; Lulworth skippers have benefited from the move away from tight grazing by sheep in the last century and recently outbreaks of myxomatosis among rabbit populations, which otherwise maintain a lower grass height. However, there is evidence to suggest that minimal grazing is not detrimental to the species, and may in fact be beneficial in that it encourages the growth of flowers that act as adult nectar sources.
Upon hatching, the 2.5 cm (1 in) long larva spins a compact cocoon on the site of the eggshell. In this, it will overwinter until around the third week of April, at which point it will eat its way out by making a small hole in the side of the sheath. The caterpillar will then search for tender Tor-grass blades and feed upon them by chewing out notches from the margin. During this time, it will live separately, within a tube composed of the two edges of a blade bound by cords of silk. Fresh tubes will be made as the caterpillar grows larger. Lulworth skipper caterpillars live in the warmest zone of a grass clump, at a height of .
The stage lasts for about two weeks, from the beginning of June onwards, until late July. It is formed inside a loose "nest" of silk and grass that is spun deep inside a tussock of tor grass. Imago begin to emerge in the early middle of July and finish emerging in the middle of September. Typically, they will live for five to ten days—the normal lifespan for a non-hibernating butterfly of the Lulworth's seasonal stage. They fly only in strong sunshine and tend to form discrete colonies, with the largest containing up to 100,000 individuals.
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