372 INSECTS INJURIOUS TO VEGETATION. , 



sluggish in their habits, fly heavily and but little, and do not at- 

 tempt to escape when touched. Most of -them are rather short 

 and somewhat flattened. They have a broad head, which, seen 

 from above, appears transversely square. The hind-body is not 

 narrowed to a point where it joins the thorax, but is as broad as 

 the latter, and is closely united to it. The antennae are generally 

 short ; but they vary much in form ; in many species they are 

 thread-like and slightly tapering ; in some, thickened or knobbed 

 at the end ; more rarely they end suddenly with a few very small 

 joints, much more slender than the rest ; they are feathered in 

 some males, and notched in the other sex ; and sometimes they 

 are forked, or divided into long branches. Their wings cross 

 and overlap each other, and cover the back horizontally when 

 closed. But the most striking peculiarity of these insects con- 

 sists in the double saws wherewith the females are provided. 

 These are lodged in a deep chink under the hinder part of the 

 body,, like the blade of a penknife in its handle, and are covered 

 by two, narrow, scabbard-like pieces. The saws are two in num- 

 ber, placed side by side, with their ends directed backwards, and 

 are so hinged to the under-side of the body that they can be 

 withdrawn from the chink, and moved up and down when in use. 

 They vary in their form, and in the shape of their teeth, in dif- 

 ferent kinds of saw-flies ; but they generally curve upwards and 

 taper towards the end, and are toothed along the lower or convex 

 edges. Each of the saws, like a carpenter's fine saw, has a back 

 to steady it ; the blade, however, is not fastened to the back, but 

 slides backwards and forwards upon it. Moreover, the saw-blade 

 is not only toothed on the edge, but' is covered, on one side, witb 

 transverse rows of very, fine teeth, giving to it the power of a 

 rasp, as well as that of a saw. 



The female saw-flies use these ingeniously contrived tools to 

 saw little slits in the stems and leaves of plants, wherein they af- 

 terwards drop their eggs. Some, it appears, lay their eggs in 

 fruits ; for Mr. Westwood discovered their young within apples 

 that had fallen from the trees before they had grown to the size of 

 walnuts. The wounds made in plants by some kinds of saw- 

 flies swell, and produce galls or knobs, that serve for habitations 

 and for food to their young. The eggs, themselves, of all these 



