6 A BOOK OF INSECTS 



remains to ensure a firm foothold. Still more valuable is 

 the insect's power of flight. Its wings enable it to 

 voyage far and wide over land and sea in search of food. 

 It has the power to colonise, to found families in 

 promising localities, to migrate, like a bird, before 

 severities of climate. Thirdly, the insect has a noble 

 head, equipped with marvellous sense-organs and a tool- 

 box mouth. The wherewithal of a sound digestion con- 

 stitutes a fourth qualification for success. It enabled 

 insects to diversify their ways of feeding as they began 

 to increase and multiply upon the face of the earth. 

 They were able to put up with what they could get — to 

 " rough it." No spot was too barren, no food too meagre, 

 for their support. Fifthly, the systems of circulation and 

 respiration which obtain among insects are highly favour- 

 able to a vigorous, pushful life. The tissues are con- 

 stantly bathed in nutritive fluid, and permeated with 

 oxygen, the inevitable result being abundant energy. 

 Ceaseless activity is a fundamental law of insect existence, 

 as one may realise by watching a bee or an ant during 

 the hours of a summer day. Ants are known to toil also 

 by moonlight in warm weather. A tired insect exists 

 only in the fancy of the poet. 



Insects undoubtedly possess great muscular force, 

 but their feats of strength have often formed the subject 

 for unwarrantable exaggeration. " liy general reasoning 

 of a quite simple kind " (I quote from " The Cockroach'' 

 by Miall and Denny) " it can be shown that, for muscles 

 possessing the same physical properties, the relative 

 muscular force necessarily increases very rapidly as the 

 size of the animal decreases. For the contractile force of 

 muscles of the same kind depends simply upon the 

 number and thickness of the fibres : i.e. upon the sectional 

 area of the muscles. If the size of the animal and of 



