LASIOCAMPIDS. 137 
bers. The moths take no food, hence they can spend all 
their energy to search for suitable places in which to deposit 
their eggs. In this manner they sometimes fly a long dis- 
tance, and especially after a time when the great majority of 
the nearly grown caterpillars had.been killed by a contag- 
ious disease; in fact it almost seems as if the moths which 
had escaped this disease realized the danger and tried to 
avoid it and to protect their future off-spring against it by 
migrating to places where the insect, and the disease, had 
not occurred for some years. Since this disease is very apt 
to occur whenever the insects have been very numerous for 
three years in succession in any one locality, we have the 
reasonable assurance that after that period the insects 
will disappear from the locality for some time. But as 
some of the healthy moths escape they start colonies 
in new regions and as the resulting caterpillars are healthy, 
they soon increase very rapidly until they are again 
killed off by the same fatal disease. All attempts to 
breed and multiply this useful disease by artificial 
means have failed thus far, but no doubt means will be 
found in future to utilize it against these destructive cater- 
pillars. In 1898 the disease appeared in a small grove of 
trees, and the writer took numerous diseased caterpillars to 
other groves infested with healthy worms. Still other 
diseased worms were sent long distances to forests invaded 
with tent-caterpillars, and wherever introduced the disease 
broke out amongst the healthy worms, and soon destroyed 
the greater majority of them. Many other forests, as 
badly infested with these worms, showed no sign of this 
disease, and it would be more than accident if such places 
had escaped while others had not. There seems to 
be but little doubt that this diseasecan be spread artificially 
in case we can find diseased worms at the proper time. 
Two breeding cages were prepared which contained the 
eggs of healthy moths; at least in the places from which the 
eggs were taken no disease appeared in the following season. 
