155 
No beetles were taken on any night when the thermometer regis- 
tered below 52*^, except May 21, when the temperature was 62° at 
9 p. m. but fell to 46*^ before morning. A cold rain or high wind 
kept them confined at night to their day-time hiding places, and they 
were never abundant on their food plants, or flying freely, unless 
the minimum temperature was at least 60^^. They appeared in great- 
est numbers on warm quiet nights following bright sunny days. 
The beetles continue feeding during rain if a storm comes up during 
a night favorable to their movements ; and even their flights are 
not wholly suppressed by moderate rain if the weather is warm. 
Modes and Pipages of Hibernation. 
Our common w^hite-grubs hibernate, in the latitude of central 
Illinois, in the two stages of larva and beetle, and in these stages 
only. In fifty-seven collections, distributed over several years, ob- 
tained by following the plow in fall and in spring, not a single pupa 
of these species has occurred, although recently transformed beetles, 
still inclosed in their pupal cells, have been collected by the hundred. 
The pupa of Lachnostcma may possibly go through the winter now 
and then, transforming the following spring, but this is certainly 
an extraordinary occurrence in our latitude, quite insignificant as a 
factor in the life history of the species. It is also a very unusual 
thing for the beetles to come out of the ground in fall. Indeed, 
those taken from the earth and placed in breeding-cages in either 
fall or early spring, commonly bury themselves without delay. Now 
and then a single specimen may be found active in fall, but we have 
seen but one such case in the course of our several years' work. The 
beetles are evidently more resistant to cold than the grubs, and do 
not attempt, as a rule, to escape by going farther into the ground 
with the approach of winter. 
During the summer most of the grubs are near the surface of 
the soil. A small percentage may be found to a depth of eight or 
even ten inches, but the average is about three inches. In late fall 
they begin to go down as a protection against the approaching win- 
ter's cold, and may reach a depth of two to two and a half feet. In 
October and November, 1905, the downward movement of the 
grubs infesting a field of corn, part of which had been completely 
destroyed by them, was followed by digging over, on each of five 
days, several areas each three and a half feet square, and counting 
the grubs e"xposed. The following table gives the dates at which 
this search was made, the average number of grubs found for each 
square of three and a half feet, the range in depth of the grubs dug 
out, and the average depth for each date. 
