358 UTILITARIAN ZOOLOGY 



bodies of the dead insects. This latter result is said to have 

 occurred on some occasions from locusts flying in a mass into 

 the sea, and their dead bodies being afterwards washed ashore." 



Of other well-known members of the present order which are 

 to be regarded as pests may be mentioned : The Earwig (Forficula 

 auricularid), which attacks flowers and fruits; Cockroaches (our 

 common species is Periplaneta orientalis), that are troublesome in 

 houses and on board ships; and the Mole- Cricket (Gryllotalpa 

 vulgaris}) which is injurious to pasture. 



Principles regulating the Methods employed in Combating In- 

 jurious Insects. These are summarized by Ritzema Bos (in Tier- 

 ische Schddlinge 2tnd Niltzlinge) under *(i) Preventive Measures, 

 (2) Curative Measures, (3) Measures which are both Preventive 

 and Curative. It may be well once more to emphasize the fact 

 that to successfully combat harmful insects (and all other pests) 

 an intimate knowledge cf their habits and life -histories is 

 essential. There is commonly, for example, some stage in the 

 development of a particular animal which can be exterminated 

 with comparative ease and at relatively small expense. This must 

 be carefully borne in mind, or it may turn out that, financially 

 speaking, " the remedy is worse than the disease ". 



(i.) Preventive Measures. Sickly plants are in many cases 

 more subject to infestation than healthy ones, and it therefore 

 follows that all the means adopted by farmers, gardeners, and 

 foresters to promote the vigour of the forms with which they are 

 concerned assist in warding off the attacks of injurious insects, &c. 

 It is also well known that seedlings are less able to resist their 

 enemies than plants in a later stage of development, from which 

 it follows that crops should be stimulated to rapid growth at the 

 time when sprouting begins. 



One of the benefits to be derived from rotation of crops is to 

 check the ravages of various injurious insects, &c., which only 

 feed upon one or a few kinds of plant. They are often, so to 

 speak, starved out. Clean seed is another important preventive, 

 for without precaution in this direction sowing may mean a dis- 

 tribution of pests as well as plants. And as during part of their 

 existence some noxious forms are harboured in straw, another 

 preventive measure is thereby suggested. 



It is also sufficiently obvious that the natural enemies of pests 

 should be protected and encouraged as far as possible. This 



