^ Insects injurious to corn. 



317 



to have taken it into his little head to perform this march at the same 

 time. This marching of the worms in an army is brought about purely 

 and simply by the scarcity of food in the place they had thus far been 

 feeding. In these marches we find millions of worms massed together 

 and all moving over the ground in the same direction, and it is this 

 habit that has given these insects the comrnon name of the army-worm. 

 No one who has not seen an army of these worms traveling in search of 

 a fresh supply of food can form any conception of the vast numbers, 

 and of the destructive work that these insects are capable of causing. 

 At such times the insects seem to be unusually hungry, and will utterly 

 destroy nearly every green vegetable 

 substance in their line of march, es- 

 pecially any members of the grass 

 family, which, of course, includes our 

 corn, wheat and other grains. 



When these insects encounter a field 

 of wheat or a corn field, they devour 

 practically every green leaf and cut off 

 the heads of the wheat. An ordinary 

 marching army of these insects will 

 completely destroy two acres of wheat 

 or early, corn in one day. When they ^jg gg.-Larva of Army-worm. 

 attack a certain field, they usually f^^^Riieylf ""''"' '''''"'^' ''''' 

 march forward as fast as they are able to devour the plants. It is usually 

 th'_ case that these army-worms develop in low places about the meadows 

 or fields where the plants are more thrifty, and should their number not 

 be unusually great, they confine their feeding to this locality ; but where 

 they occur in immense numbers, as soon as they have obtained about half 

 their larval growth, their appetites become so ravenous, and they devour 

 so much more than they did previously, that the plants in this particular 

 area are not sufficient to supply their food. It is in such cases, then, 

 that the well known migration occurs. Whether the larvae have migrated 

 or not, when they become full grown they enter the ground a little 

 ways below the surface, and wriggle their bodies back and forth in 

 order to pack the earth and make a little cell, and then presently change 

 to pupae. The larvae usually require about twenty-five days in order 

 to become full grown, and the pupae stage usually lasts about seventeen 

 days. At the expiration of this time the adult moths emerge from the 

 pupae. Hence in central Missouri we find these larvae, as a rule, march- 

 ing about the first of June. At this time the corn is young and the wheat 

 plant is in the milk stage, and should an army of these worms encounter 



