Friends and Foes 265 



leaf; or of the minute beetles, whose grubs, penetrating 

 between wood and bark, destroyed in i;8o and the follow- 

 ing years a million fir-trees in the Harz Mountains and 

 Switzerland, fifty thousand trees, chiefly oaks, more 

 recently in the Bois de Vincennes, and are causing avenues 

 of fine elms to disappear in the north of France. Green 

 fly, scale insects, slugs, wireworm, grubs, and the various 

 other plagues known to the gardener and agriculturist 

 must also be passed over, and we must go on to consider 

 by what natural means these various creatures are kept in 

 check and prevented from becoming positive enemies to 

 all vegetation, instead of merely thinning the ranks, to the 

 advantage of the survivors. 



For when one reads of flights of butterflies which take 

 days and weeks to pass, of armies of caterpillars which 

 stop the progress of railv/ay trains, and of dense clouds 

 of locusts several miles long, it is quite evident that unless 

 their increase were restricted by some very eflicient means 

 they would all more than justify the locust's boast, and 

 leave not so much as a blade of grass. 



Man is utterly unable to cope with them by any means 

 at his present disposal, and when he interferes with 

 nature's way of keeping them within bounds, he learns 

 by hard experience his own utter helplessness, and often 

 not till then. 



In the Middle Ages people seem to have had the feeling 

 that they ought to be able to control grubs and the like 

 by the mere word of command, and the chroniclers of the 

 time often give reports of the lawsuits instituted against 

 these creatures. In 1479, for example, the canton of 

 Berne was troubled with such an overwhelming plague of 

 grubs that the council petitioned the archbishop of Lau- 



