WOOLY BEARS. 81 
bers of them. Without the assistance of these beneficial 
insects the caterpillars would multiply to such a degree as 
to be soon beyond our control. This species is illustrated in 
Fig. 78. 
Fig. 78.—Spyilosoma virginica Fab.: a, caterpillar; b, pupa; c,adult. After Riley. 
THE FALL WEB-WORM. 
(Hyphantria cunea Drury). 
This is getting to be a very destructive insect in Minne- 
sota, which at present seems to be confined to plum-trees. 
Both the wild and cultivated varieties are infested, and 
toward the middle of August they are disfigured by large 
nests made by colonies of these caterpillars. When we in- 
vestigate these bulky nests, which show no regularity of 
construction like those of the tent-caterpillars, we find them 
composed of numerous smaller nests, of which the older ones 
are more or less filled with excrement, old skins, and the 
white head-plates of the caterpillars. Sometimes we find in 
them also the egg-shaped cocoons of hymenopterous para- 
sites. The caterpillars are not as social in their habits as 
those of the tent caterpillars, and they do not come and go 
to their nest in regular armies, but rather protect themselves 
when feeding by simply building a shelter over their food. 
Fig. 79, on Plate XXII, shows one of these nests. 
