There has been a considerable range expansion for Roesel's bushcricket Metrioptera roeselii in Essex since 1980, and it is often assumed that the macropterous (long-winged) form (f. diluta) has played an important role. A systematic study of the occurrence and distribution of this bushcricket in the county shows that this range expansion has corresponded with a significant increase in air temperature and the availability of tall grassland on farmland, due to the introduction of set-aside and agri-environment schemes such as Countryside Stewardship. These tall grasslands are particularly important for M. roeselii in areas of the county (e.g., the northwest) where hedgerow removal has been severe since the 1940s. This study indicates that the previous year's air temperature may be the most crucial climatic determinant of macroptery, hot weather leading to successful breeding and high population densities in the following year. These populations may then produce macropterous individuals in response to overcrowding; this may explain the occurrence of long-winged M. roeselii in years with cool and damp weather. However, this study fails to provide conclusive evidence of this due to a lack of quantitative macropter data. Nevertheless, a clear link is established between high temperatures and the early appearance of macropters, hot weather from April to July leading to accelerated nymphal development and earlier sightings of macropterous bushcrickets.