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 Tenthredinidae 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.) f ema les 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. 
