Sword-grass moth  (Xylena exsoleta)

Classified as Nationally Scarce in Great Britain (2).

Sword-grass moth adults are large, with greyish-brown wings. The forewings can vary in colour, being darker in some individuals (3). The caterpillars are plump in appearance and can grow up to 6.5 cm long. They are bright green in colour with two yellow lines passing along the back, between which are black spots with white centres. Along each side there is a white line topped with red dashes (4). The English name 'Sword-grass' is an old name for sedge, which was believed to be the foodplant of the caterpillars in 1778 when the species was given this name (5).

Unfortunately, this moth has suffered a massive decline in the UK since the 1960s. It was once widespread but has been observed in England on only a handful of occasions since 1980. It may hang on as a resident breeding species in both Wales and Northern Ireland but is not recorded often (2). It still breeds over quite a large area in Scotland and is more regularly recorded there (2).

This species utilises a variety of habitats, but tends to occur in moorland or upland sites (2).

Adults of this single-brooded species are active in September and October, and hibernate through the winter, emerging again in March and April (1), when the eggs are laid in groups (4). Caterpillars are active both in the day and night from May to July (1). In August the pupal stage develops on or below the ground (4). The foodplants of the caterpillars have not been identified (2), but may include sorrel and dock (6).

The factors responsible for the poor status of this species are not known (2).

The Sword-grass is a UK Biodiversity Action Plan (UK BAP) priority species. The Species Action Plan produced as part of this prioritisation aims to maintain the current known populations and enhance these by 2010 (2). Suitable habitat management, increasing the available area of habitat and linking fragmented habitat patches at occupied sites have been suggested as potential measures that may benefit the species (2).

Further reading on moths:
Leverton, R. (2001) Enjoying Moths. Poyser, London.
Skinner, B. (1884) Moths of the British Isles. Penguin Books, Harmondsworth

Information authenticated by Roy Leverton.

• 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.
• Larval: of the stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
• Pupal stage: Stage in 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. Skinner, B. (1884) Moths of the British Isles. Penguin Books, Harmondsworth.
2. UK BAP Species Action Plan (December 2001): http://www.ukbap.org.uk/
3. South, R. (1961) Moths of the British Isles. Frederick Warne and Co. Ltd, London.
4. Carter, D.J. and Hargreaves, B. (1986) A field guide to caterpillars of butterflies and moths. William Collins and Sons, London.
5. Marren, P. (1998) The English Names of Moths. British Wildlife, 10: 29-38.
6. Leverton, R. (2001) Enjoying Moths. Poyser, London.