Abstract
It is more than 25 years since the last review of the status of mayflies (Ephemeroptera) and stoneflies (Plecoptera) in the United Kingdom (UK). The previous review used the British Red Data Book criteria to assign conservation status to five mayfly and seven stonefly species. The criteria used for assigning the threat status in these publications had the categories Endangered, Vulnerable and Rare, which were defined rather loosely and without quantitative thresholds. The application of these categories was largely a matter of judgment, and it was not easy to apply them consistently within a taxonomic group or to make comparisons between groups of different organisms. The present review has been undertaken to provide an up to date assessment of the status of mayfly and stonefly species in the UK. The IUCN Guidelines have been revised and subsequently updated, and new information on distribution and trends is now available, making it timely to revise the status of all mayfly and stonefly species. Over 275,000 distribution records covering 51 mayfly and 34 stonefly species were analysed and new status assessments provided for these species. This process resulted in one species of stonefly and two species of mayfly being listed as extinct in the UK and a further seven species listed as being at risk of extinction, compared with five species in the previous review. A further 10 species did not have sufficient information to confidently assess their status. Twentysix species were highlighted as being either Nationally Rare or Nationally Scarce. This represents a significant increase upon the previous review when only nine species were highlighted as being Nationally Rare/Scarce.