INJURIOUS AND BENEFICIAL INSECTS OF CALIFORNIA. 



379 



THE ARGENTINE ANT" 1 

 Iridomyrmex humilis Mayr (Family Formicidse) 



(Fig. 3 80) 



Description. — The adult workers are small, dark-brown ants, living 

 in small or very large colonies. There are two other adults forms: 

 queen and male. The queen is A inch long, with the legs slightly 

 longer than the abdomen. The body is covered with silky pubescence. 

 She lays from two to fifty eggs a day. The worker is much smaller, 

 being only about half as large as the queen. There is but one caste of 

 long-lived workers. The male is a little larger than the worker, vary- 

 ing from ^ inch to ^ inch in length. The thorax, like that of the queen, 

 is noticeably enlarged, supporting four wings, the abdomen small and 

 the head short and blunt. This sex appears in the spring. The eggs 

 are elliptical, very small, pearly white and smooth, with a very thin 

 membrane which allows the developing embryo to be clearly seen. 



Fig. 380. — Worker of the Argentine ant, Iridomyrmex humilis Mayr, 

 of a mandible, showing the arrangement of the teeth. Greatly enlarged. 



and detail 

 (Original) 



Life History. — The eggs hatch in from eighteen to fifty-five days. 

 The larvae are fed by attending workers for about thirty-one days 

 during the summer, before they become full grown. As the pupa? 

 develop they become darker until they approach the color of the 

 emerging adults. This stage requires about fifteen days. The entire 

 life cycle for the worker to the beginning of the adult stage averages 

 about seventy-eight days. Egg laying begins in the spring and con- 

 tinues until winter. 



Nature of Work. — The work of the Argentine ant differs somewhat 

 in the various localities, but the insect is a serious household pest in all. 

 It invades the hives of honey bees and completely destroys or drives 

 away the bees. Probably the most serious problem in connection with 

 the Argentine ant in the Southern States is the protection which it is 

 said to give to scale insects and plant lice. The ants constantly attend 

 scale insects and plant lice, and thus keep away all forms of preda- 



= 71 Newell, Wilmon, Jr. Ec. Ent. II, pp. 172-174, 1909 



Woodworth, C. W.. Bui. No. 207. Cal. Agrcl. Exp. Sta., 1910. 



Newell, Wilmon, and Barber, T. C, Bui. No. 122, Bur. Ent. U. S. Dept. Agric, 1913 



