HYMENOPTERA 159 



Chalcis-flies (super-family Chalcidoidea) , may parasitize 

 species in many different groups, mainly of the smaller in- 

 sects. They may infest scale insects and many egg para- 

 sites belong to this division. 



Parasitic Hymenoptera of many of these groups may 

 attack other parasites. In such case they are called 

 secondary parasites. Secondary parasites may in turn 



FIG. 116. Sphinx Larva Parasitized by Braconids. 

 Pupae attached. 



be parasitized and their parasites are called tertiary par- 

 asites. It is thought that there are even quaternary par- 

 asites or forms that attack the tertiary parasites.* 



In addition to the parasitic forms, there are some 

 plant-infesting species belonging to the Chalcis-flies. These 

 may be both beneficial and harmful. The Wheat Joint- 



* "Big fleas have little fleas to bite 'em, 



Little fleas have lesser ones, and so ad infinitum." 



"So naturalists observe, a flea 



Has smaller fleas that on him prey; 

 And these have smaller still to bite 'em, 

 And so proceed ad infinitum." 



Swift. " A Rhapsody." 



" Great fleas have little fleas on their backs to bite 'em, 

 And little fleas have lesser fleas, and so ad infinitum, 

 And the great fleas themselves, in turn, have greater fleas to go on; 

 While these again have greater still, and greater still, and so on." 

 DeMorgan, " A Budget of Paradoxes," p. 377. 



