124 INSECTS 



record, and then butterflies become so plentiful that the 

 last brood of caterpillars plays havoc in our cabbage 

 fields. By this time the parasites are in evidence again, 

 and the hibernating chrysalids are as badly infested as 

 they were the year before. The parasite has accom- 

 plished its full purpose, the butterflies are not conspicu- 

 ously more abundant than they were the spring before; 

 but throughout the summer the farmer's cabbage has 

 paid the bill imposed by nature's methods. 



There is yet another factor in this connection, 

 and that is the matter of what is known as hyper- 

 parasitism, i.e., a parasite on a parasite. Not only do 

 these parasites infest predatory forms in other orders, 

 as for instance the larvae and even adult ladybird 

 beetles, but they infest primary parasites among the 

 Diptera and in the Hymenoptera, very materially re- 

 ducing their effectiveness as checks from the human 

 standpoint, but serving an important part in preserving 

 nature's balance and preventing the extermination of 

 the primary host. The terrific extent of this secondary 

 parasitism can best be illustrated by recording a 

 personal experience. I sorted out of a collection of 

 cocoons of the Cecropia moth 295 specimens that 

 were obviously parasitized. Of these seventy -six 

 specimens were infested by Ophion containing only a 

 single example to each cocoon ; the others con- 

 tained species of Spilochalcis and Spilocryptus, each 

 cocoon with a mass of at least twenty examples. Out 

 of these I bred nineteen specimens of Ophion, the 

 others dying of disease, fifty-one specimens of Spilo- 

 chalcis and 126 specimens of Spilocryptus: but in ad- 

 dition I also bred nearly 50,000 specimens of Dihrachis, 

 a secondary parasite upon the two primaries! And the 

 matter goes even further: for besides secondary par- 

 asites we may have others infesting these, or tertiary 



