208 Fiftieth Report ox the State Museum . 



Natural Agents Controlling the Army-worm. 



The inquiries are frequently made: Where do the army-worms come 

 from ? Will they be abundant next year ? The first question has already 

 been answered, but the answer to the second may not be so readily 

 given. The comparative abundance or scarcity of this insect, as well as 

 of others, from year to year is controlled by natural causes. The most 

 prominent of these are the relative abundance and quality of its food, 

 the favorable or adverse climatic conditions, and the number and activity 

 of its natural enemies. Temperature and moisture have an important 

 bearing on the production of its food-plants, and all know that without 

 an amply supply of proper food, the caterpillars would die while young 

 or immature, and no serious injury to crops would result from their 

 presence. Weather conditions have also marked effect upon insect 

 growth and development. Cold and wet serve to impair lepidopterous 

 life, and when such prevails while the insect is in its tender larval stages, 

 great mortality is the result. Hibernation is a severe ordeal for many 

 insects, and alternate freezings and thawings, to which they may be sub- 

 jected, may terminate many insect lives. It is only when the climatic 

 conditions in connection with other controlling causes are favorable 

 to the rapid growth and multiplication of the insect, that the ravages of 

 the army-worm reach the ruinous extent of the present year. Such com- 

 binations can not be predicted. They very rarely occur in consecutive 

 years. The theory has been advanced, that a dry season followed by 

 a wet one, is likely to be an army-worm year, and it is apparently borne 

 out by records made. But the attempt to predict the abundance of the 

 army-worm solely from the amount of rain-fall for the year, ignores the 

 important part that the predaceous and parasitic enemies of this insect 

 have in its control. 



The army-worm is also subject to a deadly bacterial disease, which may 

 be fatal to large numbers. In the western portion of the State, 25 per 

 cent, were killed by it in some localities (Lowe, loc cit., p. 128). Unfortu- 

 nately, the disease is only effective, it is believed, under certain conditions, 

 and these are rarely favorable in nature to any extended action, or even 

 to artificial propagation. 



Predaceous Enemies. 



Fortunately for the farmer, the army-worm has a large number of foes 



that prey upon it. Swine are said to eat them greedily, and to prefer 



them to corn. Shrews, skunks, and weasels, are reported as consuming 



large numbers. Domestic fowls, especially ducks and geese, are valuable 



