INSECT ENEMIES OF EASTERN FORESTS 297 
behaviour of the beetles while constructing it differ according to 
whether they are monogamic or polygamic. 
In the monogamic forms the female begins the burrow and does all 
or nearly all the construction work. The male may enter the new 
burrow and may assist in constructing the nuptial chamber and aid 
in the disposal of the frass from the egg gallery, but in other cases 
the only real duty he performs is fertilizing the female. The burrows 
of monogamic species have a variety of forms—simple cavities, regular 
or irregular longitudinal or transverse galleries, or forked galleries— 
and they may occur in the inner bark, in the wood, or in the pith. 
In the polygamous beetles the male begins the burrow and does all 
the early work in its preparation. Most of the males begin to leave 
the old host several days earlier than the females. They find suitable 
host material and each begins a new burrow by constructing an en- 
trance gallery diagonally through the bark to the sapwood. Here he 
excavates an irregular cavity, the nuptial chamber, and the burrow is 
then ready for the reception of one or several females, which have 
taken no part in this early work. | 
On entering the new burrow, each female begins the construction 
of a separate egg gallery leading off from the central nuptial chamber. 
The directions of the galleries, with regard to the grain of the wood, 
depend on the species of beetle. In some species the galleries have a 
general longitudinal direction, in some they may be transverse, and 
in others they may bear any relation whatever to the grain of the 
wood or bark. The completed burrow is thus more or less radiate or 
stellate in general form. The egg galleries are of uniform bore and 
are just large enough to allow the passage of the beetles. When they 
are unusually long, they may have at varying distances small alcoves, 
known as turning niches, into which the beetle may back up and re- 
verse its direction. In many galleries no such provision is made, and 
the female must back into the nuptial chamber in order to turn around. 
Polygamous beetles most commonly live in burrows of the radiate 
type but may also live in the cave type, and either type may be ex- 
cavated in the bark, the wood, or the pith. Ambrosial galleries may 
contain only females that have been fertilized before leaving the 
parent burrows, or they may contain several males and many females. 
An interesting habit shown by many monogamous species, and 
almost universal with the polygamous forms, is that of the males in 
blocking the entrance to their burrows with their own bodies, thus 
preventing the entrance of both predators and parasites. The en- 
trance of the burrows is thus rendered invulnerable to any ordinary 
attack. Many of the males die in this position, and even after death 
their bodies afford some protection to the brood within. 
From the foregoing discussion, it is apparent that the reproductive 
habits of each species are largely responsible for the type of burrow 
or engraving made by it. The burrows may be grouped in about 10 
general types, with considerable variation in each type, due to size, 
direction, and position of the component parts. 
(1) Cave Burrows.—These consist of an entrance gallery leading 
directly into an irregular cavity made by the parent beetles. In this 
the eggs are laid either in irregular masses at any part of the cave or 
in egg niches or grooves at its periphery. All the larvae may work 
together in enlarging the original cavity, or they may excavate 
