LIFE HISTORY. 



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 dep'ositing 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 incid^ation 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 workei*s, 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 tliroughout the 

 entire period of incubation. The following table shows the variation 

 in development at dift'erent seasons, together with the a\^erage daily 

 mean temperatures prevailing: 



Table II. — Duration of the egg stage of the Argentine ant at different seasons — worker. 



' 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. 



