OAK-BORERS. 55 
through it, so as to carry the egg beyond the hair-like scales with which the body is 
clothed, some of these touching adhere to it, their attachment to the body being so 
slight. 
The eggs are of a broad oval form, and about half the size of a grain of wheat, be- 
ing the tenth of an inch in length and three-fourths as thick, of a dirty whitish color 
with one of the ends black. When highly magnified their surface is seen to be retic- 
ulated or occupied by numerous slightly impressed dots arranged in rows like the 
meshes in a net. From the fact that several worms of the same size are sometimes 
met with in a single tree, indicating them all to be the progeny of one parent, it ap- 
pears that the female drops a number of eggs upon each tree that she visits, and prob- 
ably disposes of her whole supply upon a very few trees. The size of the eggs doubt- 
less renders them a favorite article of food to some of our smaller birds. And a bird 
in discovering some of these eggs will be incited thereby to search for others in the 
same vicinity, which search being successful, will be perseveringly continued so long 
as an egg can be found upon that or any of the adjacent trees. Thus it may be that 
of the whole stock of eggs which a female deposits, scarcely one escapes being picked 
up and devoured. This appears the most probable cause of so few of these worms 
being met with, although the females are so prolific. 
The worm on hatching from the egg sinks itself inward and feeds at first on the soft 
inner bark, till its jaws acquiring more strength it penetrates to the harder sap-wood 
and finally resorts to the solid heart-wood, residing mostly in and around the center 
of the trunk, boring the wood here usually in a longitudinal direction, and moving 
backwards and forth in its burrow, enlarging it by gnawing its walls as it increases 
in size, whereby the excavation comes to present nearly the same diameter through 
its whole length. In an oak in which I met with two worms fully grown and several 
others but half grown, the whole of the central part of the trunk had been exten- 
sively mined by preceding generations of this insect and was in a state of incipient 
decay ; and I thus had an opportunity to notice the fact that none of the worms were 
lying in the decaying wood, all being outside of this, where the wood was still sound. 
Hence it is evident that it is living healthy trees which this insect prefers, and not 
those which are sickly and decaying, which latter are preferred by the European 
Cossus, some authors say, though perhaps their observations have not been exact upon 
this point, for in the instance here alluded to it would have been said on a first glance 
that these worms preferred decaying wood, since the diseased heart of the tree was 
•everywhere traversed with their burrows, and the sound wood showed few of them; 
and thus no doubt in many other cases we mistake the cause for the effect, and on 
seeing semi-putrid wood filled with worm-holes, we suppose the worms have preferred 
wood of this character, when in truth it is these holes which have caused the decay 
of the wood. 
These worms are probably three years in obtaining their growth. They cast off 
their skin several times, and after the last of these moltings their color becomes 
different from what it has previously been. 
The larva previous to the last change of its skin is of a rose-red or a pale cherry- 
red color, often with a faint yellowish stripe along the middle of its back, on all 
except the three anterior rings. It is of a cylindrical form, slightly broadest ante- 
riorly and a little flattened beneath. It is divided by transverse constrictions resem- 
bling broad shallow grooves into twelve rings, which are twice as broad as long. On 
each of these rings are a few pimples of a deep purple color, regularly placed, each 
giving out a pale-brown bristle. Four of these pimples are on the back, placed at the 
angles of an imaginary square or a trapezoid having its hind side the longest, the two 
hinder pimples being larger. Small white dots confluent into broken lines may also 
be perceived, forming a transverse square in which the two anterior pimples are 
inclosed, and other dots less regularly placed surrounding the two hind pimples 
except upon their hind side. Above the breathing pores on each side is also a large 
pimple, which, upon the four rings bearing the prolegs, has a white dot in its lower 
edge, which dot does not appear in the corresponding pimples of the other rings. A 
