PHASES OF LOCUSTS 



301 



that they have hitherto been regarded as different species, which 

 has naturally resulted in confusion. 



Taking the African migratory locust (Locusta migratoria 

 migratorioides) as an example, the essential characteristics of the 

 phases may briefly be diagnosed as follows (sexual differences 

 being excluded). 



The phasis gregaria is the swarming or migratory phase which is 

 so highly destructive. It is characterised in the nymphal instars 

 by the great predominance of black and deep orange-yellow 

 coloration which develops quite independently of the nature of 

 the environment. The adults have the pronotum somewhat 

 concave, rather short and prominently constricted : there is 

 clearly no marked dorsal carina. Biometrical studies show 

 difference in the size and proportion of the tegmina and hind 

 femora as compared with those organs of individuals in the 

 solitary phase, the femora being relatively shorter and the tegmina 

 relatively longer. Colour differences are of minor importance in 

 diagnosing adult individuals of this phase, and the most reliable 

 characters are afforded by ascertaining the values of the following 

 ratios. 



Table XVII 



The phasis solitaria, or solitary non-swarming phase, is relatively 

 harmless. It is characterised by the nymphs being extremely 

 plastic in their coloration, which shows a strong tendency to 



