1 82 VIGNETTES FROM NATURE. 



their depredations, is obliged to produce an 

 enormous quantity of seeds, at a ruinous cost 

 to its constitution, most of which get eaten 

 up without doing any good at all to the 

 species. For aught we know to the con- 

 trary, these red worms may be now in course 

 of exterminating the chickweed, much as the 

 Colorado beetle would exterminate the 

 potato, or as the phylloxera would exter- 

 minate the vine, if we did not invent all kinds 

 of Paris greens and institute all sorts of 

 national quarantines to check their triumphal 

 progress. Every now and then some new 

 insect pest in this way sweeps across a con- 

 tinent, killing or threatening to kill some 

 particular species ; and when the plant which 

 it attacks is one useful to man we note and 

 chronicle its advance, which we are often 

 successful in arresting ; but when the invasion 

 is only directed against a common weed none 

 but naturalists observe its course, and even 

 they can hardly obtain the proper data for 

 estimating its advance, since nobody keeps a 



