154 SCHOOL ENTOMOLOGY 



Ants have, aside from their philosophical interest, a 

 considerable importance as economic insects. Some are 

 destructive to vegetation, others are indirectly injurious 

 because of their assistance to plant-injuring aphids, still 

 others are household pests and are injurious to foods and 

 stored products. The injurious species are most promi- 

 nent in tropical and sub-tropical countries, where it is 

 often almost impossible to protect stored products from 

 their attacks. Ant colonies, in houses, may be destroyed 

 by the use of a poisoned syrup and they may be kept 

 from tables and cupboards by so-called "Ant tape." (See 

 page 219, Part II.) 



101. Terebrantia. The Boring Hymenoptera may be 

 known by the possession of two-jointed trochanters on 

 the hind legs as well as by the lack of the sting in the 

 females. They embrace many forms and their food habits 

 are even more variable than their structures. They 

 are roughly classed as plant eaters and as parasitic 

 insects, but this classification is not entirely satis- 

 factory, because some members of the parasitic groups 

 attack plants. The plant-eaters include the Horn-tails or 

 Wood wasps (Siricidce) , the Saw-flies (Tenthredinoidea) , 

 the Gall-flies (Cynipoidea), and in part the Chalcis-flies. 

 (Chalcidoidea) . The parasitic forms are grouped as the 

 Chalcis-flies, the Ichneumon-flies (Ichneumonoidea), and 

 the Proctotrypids (Proctotrypoidea) . Many members of 

 these groups last mentioned are very difficult for anyone 

 but a pecialist to recognize. 



102. Horn-tails and Saw-flies. The Siricidce or Horn- 

 tails are named from the peculiar short, stout and 

 prominent boring organ borne by the females. They are 

 comparatively large in size, and have no constriction 

 between the thorax and abdomen. The latter character 



