PARASITES-COLLECTING 59 



From this latter list it will be seen that each para- 

 sitic fly preys upon more than one species of larva, 

 also that almost every species of larva is victim- 

 ized by more than one parasite species. It is also the 

 case that a larva may be attacked by both Diptera 

 and Hymenoptera., and by more than one species of 

 each order, and it is by no means certain that we have 

 yet found out all the species parasitic on even the 

 well-known caterpillars and eggs. For instance, it was 

 only in 1895 that Apanteles C07ig regains, Say, a hyme- 

 nopterous fly, was recorded as attacking AmpM'on 

 lies' sus^ though it was well known to live upon Ampe- 

 loph'aga mg'ron, Dol'ha hylce'us^ Frotoparce celeus, 

 P. Carolina^ Sphinx plehe'iiis, and Ceratomia catalpce. 

 One of Us found the yellow cocoons set close together 

 like a crust over the caterpillar's back, and sent them 

 to Dr. Ashmead to be identified, for we had never 

 happened to find them on any caterpillar before. Dr. 

 Ashmead wrote that Ampluon nessus was " a new host " 

 for this fly. 



It is a good plan to kill any flies that emerge from 

 a pupa or larva, and keep a specimen, keeping also a 

 record of the name of its host. This record may be 

 numbered like the specimen. A beginner cannot 

 know whether he has an old species or a new one, a 

 common host or one not known as host of that fly, 

 and some one may want that information some day. 

 We have learned by sad experience that some of the 

 most valuable chances come to those who do not know 

 enough to appreciate their value and therefore fail to 

 benefit by them. 



Very early in our work, when we were studjdng 



