LIFE HISTOKY. 
39 
Eggs are deposited at all seasons of the year. The large majority 
of them are produced during the summer, but a few are laid in warm 
spells during the winter months. The rate of deposition has not been 
determined, but one queen under observation in a cage deposited 
at the rate of 30 eggs per day, now and then suspending oviposition 
for several days at a time. 
In outdoor colonies oviposition ceases when the daily mean tem- 
perature drops below 65° F., but is usually begun again when the 
mean temperature rises above this point, regardless of the time of the 
year. 
No indication has been found of workers depositing eggs, even in 
colonies that were queenless for long periods; neither did queenless 
colonies ever rear queens from the eggs and larvae present in the nest 
at the time queenlessness occurred. 
PERIOD OF INCUBATION. 
The period of incubation varies with the season of the year, and 
in proportion as the temperature remains high or low. The shortest 
incubation period observed has been 12 days, the longest 55 days, 
and the average is about 28 days. The longer periods are doubtless 
accounted for by the entire suspension of embryonic development 
during cool weather, and it is not impossible that the viability of 
eggs may be entirely destroyed by a temperature as low as 25° or 
30° F., but on this point more data are needed. 
The period of incubation has been determined, ordinarily, by 
placing a queen and workers, but no immature stages, in an artificial 
formicary and then noting the time from deposition of the first egg 
to appearance of the first larva. This period was assumed to be the 
real period required for incubation. In other cases single groups of 
eggs have been kept under constant observation throughout the 
entire period of incubation. The following table shows the variation 
in development at different seasons, together with the average daily 
mean temperatures prevailing: 
Table II.— Duration of the egg stage 
of the Argentine ant at different 
seasons- 
-worker. 
Record No. 
From— 
To- 
Days. 1 
Average 
daily 
mean 
tempera- 
ture 
during 
po*-iod. 
Average 
daily 
mean 
humid- 
ity. 
l 
Oct. 1,1907 
Dec. 22,1907 
Mar. 14,1908 
May 1,1908 
July 20,1908 
July 25,1908 
June 30,1908 
July 24,1909 
Nov. 15,1907 
Feb. 14,1908 
Apr. 9, 1908 
May 23,1908 
Aug. 10,1908 
Aug. 12,1908 
July 18,1908 
Aug. 5, 1909 
4oh 
55" 
27 
23 
22 
19 
19 
12 
°F. 
( 2 ) 
( 2 ) 
70.3 
74 
81 
81 
81.1 
82.5 
Per cent. 
3 
4 
6 
68 9 
7 
8 
81 5 
12 
14 
1 Average days, 27.8. 
2 Cages kept in office; record of exact temperatures not available. The balance of the records were made 
in the " formicarium " and the recording instruments kept in the same room with the cages; hence the 
temperature and humidity records are correct for the exact location of the eggs under observation. 
