WHEELER— THE PARASITIC ACULEATA. 35 



with their hosts. The other class of parasitoids is represented by 

 the Aculeates which have sprung directly from their host species 

 (intraspecific parasitoids), though they may subsequently acquire 

 hosts among other species of the same genus or of other genera and 

 may in turn be the ancestors of parasitic species. 



3. The derivation of all the existing Aculeata from primitive 

 insectivorous wasp-like ancestors may account for the retention of 

 a rather uniform pattern of behavior among the parasitic species. 

 The parasites, both among the solitary wasps and the solitary bees, 

 behave in a very similar manner, though the former are reared on 

 insect prey, the latter on pollen and honey. In both groups the 

 object of the parasite is to secure the provisions accumulated by the 

 host for its own progeny. This involves a destruction of the egg 

 or young larva of the host. The social parasites, however, have 

 passed beyond this destruction of the host brood to a stage involving 

 the fostering of the host brood as a means of insuring the rearing 

 and alimentation of their own young. This change may have been 

 due in the first instance to the formation of trophallactic relations 

 between the parasite and the host brood. 



4. The origin of parasitism among the Aculeata may be attribu- 

 ted to urgency of oviposition and temporary or local dearth of the 

 supply of provisions for the offspring. 



5. In all the different forms of parasitism among the Aculeata, 

 there are traces of the primitive predatism or parasitoidism from 

 which it arose, although in some of the social parasites this is repre- 

 sented only by the aggressive or conciliatory intrusion of the re- 

 cently fecundated female into the host colony. Even the more ex- 

 treme forms of behavior, such as those of the temporary and per- 

 manent social parasites, were derived from predatory behavior like 

 that manifested by Formica sanguinca and its various subspecies 

 and varieties. 



6. Although many cases of parasitism are known to occur among 

 the Aculeata, and although many others will doubtless be discovered 

 in the future, nevertheless the total number must be small in com- 

 parison with the thousands of nonparasitic species. Contemplation 

 of such a series as we find among the ants, beginning with Formica 

 sanguinca, which is an abundant, vigorous and aggressive species 



