Colour polymorphism and substrate preferences of the blue-winged grasshopper oedipoda caerulescens on Jersey, Channel Islands

Many grasshopper species are known to demonstrate colour polymorphism although only a select few
have been studied in any detail. Controlled laboratory experiments and those involving nymphs have
been favoured over extensive work in the field with adult insects, limiting the comparative value of
the results. A number of species in the grasshopper family Acrididae are known to exhibit intraspecific
variation in the form of colour polymorphism and demonstrate crypsis and a preference for certain
substrates. One of these is Oedipoda caerulescens which, despite a lack of previous research, has
demonstrated these capabilities, although never in an island setting.
To investigate whether populations of O. caerulescens on the island of Jersey also demonstrate these
tendencies across and within a selection of sites I captured and photographed individuals of the species
and recorded their resting substrate. Using this approach, I found that the grasshoppers were present
in significantly higher numbers on 50-70% areas of open ground, with a preference for low level
heterogenous vegetation, supporting findings from previous studies. This was in contrast to other
grasshopper species which were more generalist in their substrate selection. O. caerulescens
demonstrated clear colour polymorphism and were segregated into colour morph categories based on
detailed image analysis. A significant relationship was found between colour morph group and location
within which they were found suggesting that morph-specific preferences are present for O.
caerulescens on the island. Morphological size of individual was also found to vary significantly across
sites, outside of the clear sexual dimorphism discovered.
By focusing on this understudied species on Jersey, at the southernmost location within the British
Isles, this study provides a more comprehensive view into the preferred habitat of O. caerulescens to
enable effective management and provide much needed information on insular colour polymorphism.
The results can then assist in local conservation measures for not only this insect species but those
sharing the same habitats.