Ennomos subsignaria (the elm spanworm) is a North American (Canada and USA) moth which intermittently reaches outbreak densities, causing serious defoliation of hardwood forests in parts of its native distribution. 

This moth was identified as a serious pest during the compilation of a Defra list of pests of Fraxinus created during 2016. There is one interception reported in the literature from 1984 (on asparagus fern at Convent Garden market, London), but no further interceptions are known. Ennomos subsignaria is currently listed as a provisional quarantine pest (PQP). 

Untreated wood in the rough1 and fuel wood2 were identified as the most likely pathways of entry – rated as moderately likely with medium confidence. It was considered that this pest would be likely to establish in the UK if it entered. The impact this pest could have in the UK was rated as large but with low confidence as it is very unclear whether E. subsignaria would ‘outbreak’ as it does in its native distribution.