Ashworth’s rustic  (Xestia ashworthii)

Classified as Nationally Scarce in Britain (4).

Adult Ashworth’s Rustic moths have blue-grey forewings with variable blackish flecking. The hindwings are pale and silky in appearance (2). The caterpillar grows up to 40 mm in length. When fully grown, it has a bright reddish brown head and a dark grey body that may have a green or purplish tinge in some individuals. A double row of black dashes passes along the back (3). Younger caterpillars are mainly green (5).

In Britain, this moth is found only in mountainous parts of north-west Wales (3), where it has a wide distribution (4). It is locally common in some areas, including Caernarvonshire, Merionethshire and Denbighshire (2). It extends throughout Europe from Scandinavia to Turkey and the Caucasus, Russia (4), but is very localised (5).

Typically inhabits south-facing slopes on slate and limestone grasslands (4).

Adults of this single-brooded moth are present from mid-June to August and are attracted to light (2).The eggs are laid in July on the foodplants, which include common rock-rose (Helianthemum nummularium), wild thyme (Thymus serpyllum), harebell (Campanula rotundifolium), and a range of other plants. The young caterpillars feed for a period before going into hibernation. They emerge the following spring and begin to feed again. They are active during the day, and also at night if the weather is warm enough. Pupation takes place in May, either in the soil or beneath moss. The adult moths emerge from the pupa in June or July (3).

It is believed that over-grazing by sheep is the main threat affecting this moth (4).

Ashworth’s Rustic is a priority species under the UK Biodiversity Action Plan. The Species Action Plan aims to maintain the current range of this moth. Some of the sites supporting this species are nature reserves or Sites of Special Scientific Interest (SSSIs), and so the species receives a level of protection in these areas. Regular monitoring is required to accurately determine and keep track of the status and range of the species (3).

To learn more about butterfly and moths conservation visit:

• Butterfly Conservation:
  www.butterfly-conservation.org

Information authenticated by Roy Leverton with the support of the British Ecological Society:
http://www.britishecologicalsociety.org

• Hibernation: a winter survival strategy characteristic of some mammals in which an animal’s metabolic rate slows down and a state of deep sleep is attained. Whilst hibernating, animals survive on stored reserves of fat that they have accumulated in summer. In insects, the correct term for hibernation is ‘diapause’, a temporary pause in development and growth. Any stage of the lifecycle (eggs, larvae, pupae or adults) may enter diapause, which is typically associated with winter.
• Pupa: stage in an insect’s development when huge changes occur, which reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis.
• Pupation: the process of becoming a pupa, the stage of an insect’s development, when huge changes occur that reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis.
• Single-brooded: Also known as ‘univoltine’. Insect life cycle that takes 12 months to be complete, and involves a single generation. The egg, larva, pupa or adult over winters as a dormant stage.

1. ITIS, the Integrated Taxonomic Information System (September, 2009)
   http://www.itis.gov
2. Skinner, B. (1984) Colour identification guide to moths of the British Isles.Penguin Books, Harmondsworth.
3. Carter, D.J. (1986) A field guide to caterpillars of butterflies and moths in Britain and Europe.Collins, London.
4. UK BAP Species Action Plan (October, 2003)
   http://www.ukbap.org.uk
5. Leverton, R. (2004) Pers. comm.