Insects of mesic and hydric habitats may be affected by increased frequency of summer droughts brought about by climate change, in addition to habitat degradation caused by scrub encroachment. The common green grasshopper Omocestus viridulus prefers moist grassland and is relatively rare in the County of Essex, perhaps being limited by low precipitation in southeastern England. The abundance and distribution of O. viridulus populations were compared for high- (Epping Forest) and low-precipitation areas using Geographic Information Systems (GIS) software. Populations were aggregated in Epping Forest (population isolation: 1 km), a high precipitation area (ca 69 cm precipitation/yr), and present on both well and poorly drained soils where acid grassland/wet heathland occurred. Outside of the Forest, where precipitation was generally lower (ca 58 cm/yr), populations of this grasshopper were highly isolated (isolation: 4 km) and more often present on clay soils with high water retention in winter/early summer than on well-drained soils. However, there was no significant difference in the abundance of this grasshopper within Epping Forest or outside it, and there has likely been an overall decline of 50% since 1997 for this insect in Essex Co.

The decline has partly occurred due to unmanaged scrub encroachment and loss of favorable open grassland/wet heathland habitat. Intensive grazing (particularly by large numbers of rabbits Oryctoloagus cuniculus), regular mowing, and trampling by walkers, led to the creation of short swards (< 10 cm in height) in midsummer, effectively extirpating this tall-grassland grasshopper from many of its former sites not threatened by natural succession to woodland.

Unfortunately, the predicted decline in summer rainfall may lead to this grasshopper becoming scarce in southeastern England, outside of relatively high precipitation areas such as Epping Forest. Given concern about this grasshopper it may be important to prevent further drainage of ecologically valuable wetlands and to promote appropriate conservation management of the remaining sites (such as cattle grazing in Epping Forest). Large-scale wetland creation should allow populations of this declining grasshopper to exist in a changing climate.