THE AHMY WORM. 341 



mysterious instinct to convey the order for marching, else 

 why have fields been left untouched by them for so many 

 years, only to forsake their normal habits, for reasons that we 

 can only conjecture, after so long periods of time? The 

 theory that climatic influences determine the years when 

 the army worm Avill become migratory is a good one ; but 

 there are questions unanswered as to how such influences 

 operate to change them from their normal state and deter- 

 mine them to migrate, and what inducements are presented 

 by heat or cold, a wet or a drj' season, to cause them to 

 move to other lands for food than those upon which they 

 have remained for years. The means for destroying them 

 suggested by different writers are, perhaps, as good as any 

 that I can recommend, — such as ploughing deep furrows and 

 making the side of the furrow towards the field to be pro- 

 tected perpendicular, and digging deep holes about fifty feet 

 apart in the furrow, so that the worms, failing to climb the 

 perpendicular side and moving along to find a better place 

 to get over, fall into the holes, in which they can easily be 

 desiroj^ed by pouring kerosene upon them and burning them. 

 Some recommend rolling the field upon which the worms are 

 found ; but this method of destruction is by no means cer- 

 tain, as many will escape. Paris green and London purple 

 have also been used quite successfully. Harris recommends 

 that the hogs be turned in upon them as soon as the crop 

 is removed, but I fail to see the benefit when the worms 

 have gone on, as they must have done, to other fields, and 

 there is no certainty that they will coma again for years. 

 He also recommends that the chickens, turkeys and ducks 

 be turned in upon them. These will help to destroy them, 

 but will not exterminate them. The ploughing of furrows, as 

 already described, is the most sure means to stop them in 

 their march and save other fields from their depreciations. 

 It has also been recommended to burn over the fields in the 

 fall of the year, so as to destroy the old stubble and tufts of 

 grass, etc., which reconnncndation I should approve, for it 

 may destroy some of the eggs and larvte of the army worm, 

 and most certainly will destroy the pupa and larvae of other 

 insects injurious to vegetation. But Prof. Riley's advice to 

 burn over the fields in the early spring is certainly more 



