FIGS. 3 and 4—Mines of Corthylus punctatissimus.
It will be seen that with few exceptions, the most important of which is shown in Fig 4, all the excavations (including both the horizontal canals and their vertical off shoots) are made in the sap-wood immediately under the bark, and not in the hard and comparatively dry central portion. This is, doubtless, because the outer layers of the wood are softer and more juicy, and therefore more easily cut, besides containing more nutriment and being, doubt less, better relished than the drier interior.
This beetle does not bore, like some insects, but devours bodily all the wood that is removed in making its burrows. The depth of each vertical tube may be taken as an index to the length of time the animal has been at work, and the number of these tubes generally tells how many inhabit each bush, for as a general rule each individual makes but one hole, and is commonly found at the bottom of it. All of the excavations are black inside.
The beetle is sub-cylindric in outline, and very small, measuring but 3.5 mm in length. Its color is a dark chestnut brown, some specimens being almost black. Its head is bent down under the thorax, and cannot be seen from above (see Fig. 5).
FIG 5.—Corthylus punctatissimus.
Should this species become abundant and widely dispersed, it could but exercise a disastrous influence upon the maple forests of the future—G. Hart Merriam, M D, in American Naturalist.