Northern Ireland's Priority Species

Chesias legatella – streak

Chesias legatella

Chesias legatella (Denis & Schiff., 1775)
Family: Geometridae

The distinctive features of this little moth are its long narrow grey-brown wings and tent-like resting posture. It is on the wing from mid September to mid November near bogs, woodland areas and disturbed and abandoned ground where its foodplant, broom, can be found. A Northern Ireland Priority Species because of major declines detected elsewhere in the UK. At present such data does not exist for Northern Ireland.

In brief

  • This is a notable moth with a south western distribution in Northern Ireland
  • Has a single generation on the wing in autumn from mid-September to mid-November
  • It is attracted to light
  • A Northern Ireland Priority Species because of declines detected in other parts of the UK where it has undergone a 66% decline over a 25 year period. There is no evidence as yet that the species has exhibited a similar decline in Northern Ireland but as we are part of the UK it has been included on the Priority List

Species description
A member of the Geometridae yet unusually for that family, it rests with its wings held tent-like along the length of its body. The forewings are rounded and tapering and are generally brown with a long white streak running along the length of the wing and an elliptical central mark. The overall colour may vary slightly buy the markings remain the same.

Life cycle
Adults are on the wing from mid-September to mid-November. Eggs are laid on broom and spend the winter on the foodplant. The larvae are active May and June then pupate underground.

Similar species
It is unlikely that this moth could be confused with any other moths that occur in Northern Ireland.

How to see this species
A good place to look for this moth is Annagarriff Wood NNR in Peatlands Park. Adults may be found resting on broom after dark. The moth will also come to light often a considerable distance from the nearest broom.

Current status
Predominantly a south-western species in Northern Ireland. No-longer reported from its former sites in Londonderry and Fermanagh. Being an autumn species it is likely to be under-recorded.

Why is this species a priority in Northern Ireland?

  • Listed as a UK Priority Species and therefore on the Northern Ireland Priority List by default
  • Rapid decline (66% over 25 years 1968-2002) assessed using Rothamstead trap data

Threats/Causes of decline
It is thought to be declining in the UK as a result of many factors, including habitat change, pollution and the use of pesticides.

Conservation of this species

Current action
In Northern Ireland there are no specific actions proposed for this species. General management for Biodiversity such as leaving weedy margins on roadsides, woodland rides and in gardens will help maintain the species.

  • Occurs on some ASSIs

Proposed objectives/actions

  • Increase Rothamstead Trap network to gather data on status
  • Encourage submission of records to the Moth recorder

What you can do

  • Report all moth sightings to the Moth Recorder for Northern Ireland, Andrew Crory, or use the Butterfly Conservation Northern Ireland (BCNI) sightings web page at The BCNI database is managed by CEDaR and these records will then be used to update the Butterflies and Moths of Northern Ireland website.
  • Join Butterfly Conservation. Butterflies and Moths are in serious decline — with your support Butterfly Conservation can take action to reverse this.

Further information

The Butterflies and Moths of Northern Ireland

MothsIreland Website

The state of Britain's moths - an explanation as to how declines have been calculated

Background information on the Rothamstead Trap Surveys

UK Moths Website with an up-to-date distribution map

Bayne, E.S.A. (1964). A revised catalogue of Irish macrolepidoptera (Butterflies and Moths). EW Classey, Hampton, Middlesex.
Porter, J. (1997). The colour identification guide to caterpillars of the British Isles. Viking, London.
Skinner, B. (2009). 3rd revised and updated edition. The colour identification guide to the moths of the British Isles. Apollo Books.
Thompson, R. & Nelson, B. (2006). The Butterflies and Moths of Northern Ireland. NMNI, Belfast.
Waring, P & Townsend, M (2009). 2nd edition. Field Guide to the Moths of Great Britain and Ireland. British Wildlife.

Text written by:
Allen & Mellon