No. 637] 



PARASITISM 



'17) to be parasitic, and a few other families nearly all of 

 somewhat doubtful affinities. Thus of the nearly one 

 hundred families included in the order, between forty 

 and fifty are composed either entirely or almost exclu- 

 sively of genera with parasitic habits, the remainder 

 being phytophagous or predatory with isolated cases of 

 parasitism, among both the predatory series, and one of 

 the phytophagous ones. 



Considering these larger groups, the suborders and 

 superfamilies, more in detail we find that the most prim- 

 itive of all kno\ra Hymenoptera, the suborder Chalasto- 

 gastra, are phytophagous. Of these, about a dozen 

 families, comprising the sawflies or superfamily Tenthre- 

 dinoidea, are almost exclusively defoliating forms, feed- 

 ing in their larval stages on the leaves of various flower- 

 ing plants. Another family, the Siricidae, feeds inter- 

 nally on the tissues of woody plants, and, at least so far 

 as food-habits are concerned, there are two other fami- 

 lies which form a transition between the saA\^ies and 

 wood- wasps. It is in the groups above these that the 

 parasitic habit appears, and with the possible exception 

 of one family, the Oryssidae, to be mentioned later, all 

 these groups are usually associated as a second suborder, 

 Clistogastra, contrasted to the more primitive Chalasto- 

 gastra. Among them several groups of families, con- 

 \ '^'uiently classed as superfamilies, are three extensive 

 parasitic ones : first, the Ichneumonoidea, comparatively 

 large species comprising about half a dozen families; 

 second, the Chalcidoidea, represented by small or minute 

 species comprising fully a dozen families; third, the 

 Serphoidea another half dozen, mainly very small species. 

 Together with a part of the Cynipoidea, these form the 

 enormous complex commonly known as the Hymenoptera 

 Parasitica. All are quite closely related, but rather easily 

 grouped and distinguished, in spite of certain annectant 

 and aberrant families. 



The habits of the several series are also very uniform. 



