64 INSECT RECORD FOR 1899 



A series of observations made upon a large number of nests 

 just before the period of pupation showed that more than 

 ninety per cent of the caterpillars present had been killed by 

 this disease. As a result there were few caterpillars crawling 

 along the roads in early June, although during previous sea- 

 sons great numbers were to be seen at that time/' It is pos- 

 sible that in other localities the destruction may have been 

 largely brought about by parasites. 



This sudden decrease in numbers is an illustration of what 

 commonly takes place with most of our noxious insects when 

 they have been extraordinarily abundant for several seasons. 

 The causes that bring about the decrease are not always the 

 same, and definite knoAvledge of them is seldom obtained. 

 It is probable that a predisposing cause is the lessening of 

 vitality because of the limited food supply, and many sorts of 

 parasites are nearly always at work to keep the pests in check. 

 After such a sudden check only a few of the insects remain; 

 these continue to feed and to breed, gradually increasing from 

 season to season, until after a series of years the insect again 

 becomes destructively abundant. 



The point which needs especial emphasis, however, is that 

 the best time to fight an insect is when it is thus at its lowest ebb. 

 Thus when these caterpillars are as scarce as they were in 1899 

 every colony destroyed reduces by so much the recuperative 

 powers of the species; it is the time for the stitch that shall 

 save m.any more than nine. Each caterpillar that matures 

 into a female moth will lay two hundred or more eggs for the 

 next season's crop, and about half of the progeny of these eggs 

 will in turn develop into other female moths that will lay two 

 hundred or more eggs, and so the increase will continue in 

 geometrical progression until in eight or ten years the pests 

 will again become destructively abundant, and people will 

 begin to destroy them. But they should instead destroy them 

 during these years of scarcity, when every colony destroyed 

 means as much as the destruction of a hundred colonies ten 

 years hence. 



During the abundance of these Tent Caterpillars certain 

 birds — especially the Baltimore oriole and the cuckoos — ^had 



