270 



THE BIOLOGY OF INSECTS 



in ants, and bees, and wasps the vertical dimension of the 

 abdomen approaches, equals, or exceeds the horizontal, as 

 it does among the more highly organised members of the 

 various groups of two- winged flies — gnats, midges, and the 

 house-fly group. Similar proportions characterise most of 

 the Lepidoptera (moths and butterflies). In dragon-flies 

 also the body is, as a rule, deeper than broad ; these insects 

 have elongate abdomens which being narrow offer Httle 

 resistance to the air in swift flight ; it is interesting to 



r«^' 



Fig. 67. — a, Bed-bug (Cimex lectularius) , dorsal view, X 5 ; 6, diagram- 

 matic cross-section of Cimex to show dorso-ventral flattening ; c. Dog- 

 flea {Ctenocephalus cams), lateral view, X 12 (from L. O. Howard); 

 d, diagrammatic cross-section of Flea to show lateral flattening. 



remember that their grubs crawling on the bottom of 

 pools and streams have bodies often distinctly broader than 

 deep. 



In contrast to the flattened cockroaches, the grasshoppers 

 and locusts, belonging to the same order (Orthoptera) as 

 they, have bodies distinctly deeper than broad. These 

 insects are often strong fliers, and instead of running along 

 the ground, they spend much of their time crawling on the 

 stems and leaves of plants, whence by the action of their 



