464 Saw-flies, Gall-flies, Ichneumons, 



relationship. For example, the Proctotrypidae are held by Ashmead to be 

 more nearly truly related to the wasps and to the gall-flies (Cynipidae) than to 

 the other parasitic Hymenoptera, as the Chalcididae, Braconidae, and Ichneu- 

 monidae, with which this table groups them. The families composing the 

 superfamilies Sphecina and Vespina, as separated by the character used 

 in the key, are differently divided in Ashmead's superfamilies Sphecoidea 

 and Vespoidea, and the families Tenthredinidse and Siricidae are replaced 

 by the superfamilies Tenthredinidoidea and Siricicoidea, each containing 

 several families. I only need to repeat what I have often said before, namely, 

 that at best the keys and tables used in this book, as in most other insect manu- 

 als, to assist the student in his work of classifying insects are primarily things 

 of convenience, taking advantage of obvious but often superficial and adapt- 

 ively acquired likenesses and differences, rather than attempts to offer a 

 true genealogical arrangement of the various groups. 



The saw-flies, Tenthredinidae, are the simplest Hymenoptera ; they show 

 no such extreme specialization in habit or structure as that possessed 

 by the host of parasitic species, or by the "intelligent" groups, the ants, 

 bees, and wasps. They compose a large family, 600 species being known 

 in this country, but one of singular unity. The adults are much alike in 

 appearance, and the larvae all agree in their salient characters of structure 

 and habit. Despite the large number of our species, comparatively few 

 are known to the general observer, and these almost solely because of the 



injurious habits of their larvae. These larvae 

 are the familiar rose-, currant-, pear-, larch-, 

 and willow-slugs. They are soft bodied, 

 naked, slug-like or caterpillar-like creatures, 

 usually with six to eight pairs of prop-legs 

 besides the three pairs of true thoracic legs, 

 and are voracious devourers of green leaves. 

 They may be distinguished from lepidopterous 

 larvae by their usual possession of more than 

 five pairs of prop-legs and by their having 

 but a single ocellus on each side of the head 

 FIG. 651. A saw-fly, Allantus instead of several. The eggs are laid by the 

 basillaris. (Twice natural size.) females in little pockets cut in tender stems or 

 in the leaf-tissue, usually on the under side, by means of the famous "saws" 

 which have given the insects their vernacular name. These saws are a pair 

 of small slightly chitinous pieces, finely serrate on the outer margins, which 

 are carried by the last abdominal segment and can be thrust out and moved, 

 saw-like, up and down. The larvae, or slugs as they are often called 

 because of their shape and the slimy secretion which covers the body of some 

 kinds, usually "skeletonize" the leaves, i.e., eat away only the soft tissues, 



