16 THE ARMY-WORM. 
their presence was discovered. Some fields, that looked very 
promising in the distance proved on closer examination to 
be very badly injured by having the berries exposed to the 
drying influence of sun and wind which shrunk them badly. 
A closer inspection of all fields showed at once that the 
worms had been at work for some time; in fact they had 
eaten up all the foliage and the ground was thickly covered 
with bits of leaves and the frass or droppings. In most of 
the fields the caterpillars were not forced to migrate on ac- 
count of lack of food, as enough of it was still left to enable 
the almost full-grown worms to mature. It seems a sort of 
instinct that prompts them to move away from such fields 
and to move toward new pastures. The armies thus formed 
are not composed even of social insects such as the tent- 
caterpillar, but are more like a mass of individuals routed 
by a common enemy. All worms run away and do so re- 
gardless of their neighbors. When 
we look into the matter a little 
more carefully we find, as a gener- 
al rule, that it is not simply hun- 
ger that prompts them to wander, 
but that they are frequently har- 
a of Beh etl Hepes assed by numbers of parasitic in- 
worm. Enlarged. After Walsh. sects, Out of ten worms picked 
up we may find at least six or more that harbor 
in their inside the maggots of flies or of small 
parasitic wasps. In one case fifty worms were picked up at 
random and forty of them showed the peculiar china-white 
and glossy eggs of a flyshown in fig. 8. The adult tachina- 
fly (Exorista leucanie Walsh.), a little larger than a common 
house-fly, could also be observed in large numbers near the 
army-worms. It would dart toward an intended victim 
and notwithstanding the fact that this always tried to es- 
cape, the fly would succeed in fastening one or more eggs 
uponits neck. The maggots hatching from such eggs pen- 
etrate into the worm and there feast upon the material 
stored up to produce the future wings and other organs of 
the adult army-worm or moth. Other parasites were also 
very numerous, but their methods can not as readily be ob- 

