398 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 
Egg laying begins in the earl}^ part of June. The first evidence the 
writer noticed in 1919 was on June 6, when a number of punctured 
twigs were found on several varieties of trees and shrubs at Chevy 
Chase Circle, but no particular search was made for them earlier 
than this date. B3' June 10 egg laying was at its height. The females 
could easily be watched at work, taking flight only from actual in- 
terference. They usually select twigs of last year's growth, but often 
use older ones or green ones of the same season. In the majority of 
cases the female works outward on the twig ; but if this is a rule, it 
is a very loosely observed one, for many work in the opposite direc- 
tion. 
Each nest is double ; that is, it consists of two chambers having a 
common exit, but separated by a thin vertical partition of wood 
(pi. 4, D and F). The eggs are placed on end in the chambers 
in two rows, with their head ends downward and slanted toward the 
door. Generally there are 6 or 7 eggs in each row (E), making 24 
to 28 eggs in the whole nest, but frequently there are more than this. 
The wood fibers at the entrance are very much frayed out by the 
action of the ovipositor and make a sort of fan-shaped platform in 
front of the door, where the young shed their hatching garments 
on emerging from the nest. The series of cuts in the bark eventu- 
ally runs together into a continuous slit, the edges of which shrink 
back so that the row of nests comes to have the appearance of being 
made in a long groove {A, B, C). This mutilation kills many twigs, 
especially those of oaks and hickories, the former soon showing the 
attacks of the insects by the dying of the leaves. The landscape of 
oak-covered regions thus becomes spotted all over with red-brown 
patches which often almost cover individual trees from top to bot- 
tom. Other trees are not so much injured directly, but the weakened 
twigs often break in the wind [ind then hang down and die. 
An ovipositing female finishes each egg nest in about 25 minutes; 
that is, she digs it out and fills it with eggs in this length of time, for 
each chamber is filled as it is excavated. A female about to oviposit 
alights on a twig, moves around to the undersurface, and selects a 
place that suits her. Then elevating the abdomen, she turns her 
ovipositor forward out of its sheath and directs its tip perpendicu- 
larly against the bark. As the point enters it goes backward, and 
when in at full length the shaft slants at an angle of about 45°. 
The following detailed observations were made on a female who 
had already finished several nests of a series. In beginning the new 
nest she first made three partial insertions of the ovipositor, draw- 
ing it out entirely after each slow penetration. At the end of the 
first five minutes she finally worked it in to its full length. Then, 
during five minutes more, it was pulled out and worked in again 
