io8 TRUE TALES OF THE INSECTS. 



genus Caloptenus also belongs to Acridiides. Several 

 species of this genus are injurious in North America, 

 but the migratory habit and great destructive power 

 belong essentially to the Rocky Mountain Locust, the too 

 famous Caloptenus spretus. While none other compares 

 with it there in the vastness of its movements, or the 

 injury which it inflicts, it, nevertheless, is a comparatively 

 small, inconspicuous species, its slender brownish body 

 seldom exceeding an inch and a quarter in length. We 

 ascertain plainly from the above facts that the migratory 

 species of Acridiidse are not limited to any one genus or 

 group of the family ; and it is evident, therefore, we must 

 look to something else than such anatomical character- 

 istics or differences as distinguish the groups for the 

 cause of the migratory instinct. 



We should bear in mind this equally well established 

 fact that locusts of the migratory species exist in countries 

 without giving rise to swarms, or causing serious injuries; 

 thus P. cinerascens is always present in different localities 

 in Belgium, and does not give rise to swarms. 



Occasionally individuals of these migratory species 

 penetrate to our shores. In 1869 specimens of Schisto- 

 cerca peregrina occurred in various parts of the country, 

 having in all probability arrived by crossing the German 

 Ocean, and P. cinerascens and P. migratorius have been 

 met with ; but Britain is now exempt from the ravages 

 of locusts. 



