244 NORTH AMERICAN INSECTS. 
Saw-wasps (‘Tenthreds). 
These insects are distinguished by the double saw at the 
extremity of the hind body, with which all the females are 
provided, and with which they cut, like a carpenter, little 
slits in the stems and leaves of plants, into which they drop 
their eggs. The larve of the Saw-wasps exactly resemble 
caterpillars, and they feed upon the leaves of those plants 
upon which their mother had glued her eggs, that is, upon 
which they were born. ‘They cast their skin four times, 
and, when fully grown, some species go into the ground in 
order to make their cocoons; while others metamorphose 
and fasten their cocoons on the stem of a plant, like the 
caterpillars of butterflies. 
The Exrm-tree Saw-wasp (Cimbex Ulmi) 4s one of the 
largest insects of this family. It is about one inch long, 
and its wings expand about two inches. Its head and tho- 
rax are black, the hind body blue, the antenne of a nankeen 
color toward the top and dusky at the base, the feet pale 
yellow, and the legs black. The female may be seen de- 
positing her eggs, early in June, upon elm-trees, the leaves 
of which serve as food for the insect and her offspring. 
The caterpillars which issue from these eggs are of a green- 
ish-yellow color, and have twenty-two legs. When fully 
grown, they descend from the tree, conceal themselves under 
the fallen leaves on the ground, and there spin their cocoon, 
within which they remain during the whole winter, and 
until the following May or June, when the perfect insect 
makes its exit. 
The Wood-wasps are the most destructive insects of this 
whole order, and often do great injury to our forest, as well 
as our ornamental and fruit trees. Perhaps the most con- 
spicuous insect of this species in this country is 
The Piceon Tremex (Zremex Columba), Fig. 69. This 
insect is more than one inch long, and, like the whole fam- 
