CHAPTER II 



THE HATED INVADER 



Habits of the Argentine Ant a Menace to Pacific Coast Homes 



When these household pests, the Argentine 

 ants, Iridomyrmex lmniils. have established a 

 line of travel from their nest to some place 

 where they have discovered food to their 

 liking, it is interesting to watch them going 

 back and forth. In all probability the ants 

 returning to the nest are conveying food for 

 their larvae and also for the nurses, or such 

 individuals of the colony that remain in the 

 nest to take care of the numerous infant ants. 

 However, this species of ant is so minute it 

 is impossible to determine without the aid 

 of suitable magnifying instruments and other 

 agencies whether the ants are carrying food 

 or not. 



Having discovered a place in our basement 

 where the ants had established a line of travel 

 to the apartments above, using the smooth 

 surface of the tongue and grooved board wall 

 for the roadway, I was afforded an oppor- 

 tunity for close observation of the move- 

 ments of the ants to great advantage and 

 with no discomforts. 



After watching the ants and studying their 

 actions for several days, and making some 

 experiments to test their sense of smell and 

 location, I was ready to concede as true, ex- 

 cepting in the case of some wasps, the claim 

 of certain eminent entomologists who have 

 given years to the study of these insects that 

 the ant family possess the greatest intelligence 

 of all insects. 



While traveling in either direction, up or 

 down, I noticed that both of the antennae 

 or "feelers" of the ants were continuously 

 active and were used not altogether unlike a 

 blind man hurriedly feeling his way with a 

 cane in each hand. It is a mooted question 

 as to how well some species of ants can see, 

 but it is conceded by the best authorities that 

 some are practically blind. Whether the 

 Iridomyrmex can see or not I was unable to 

 determine, but from the way they used their 

 antennae and results obtained its kind seemed 

 to be in little need of eyesight. 



The roadway or space occupied by the 

 column of ants on the wall did not exceed 

 three-eighths of an inch in width at any 

 place between the ceiling and the floor, the 

 points where they emerged and disappeared, 

 in the going and coming; and a remarkable 

 thing about this roadway was that so far as 

 the ants were concerned, it was as well de- 

 fined as any highway in the State of Cali- 

 fornia, although so far as I could see there 

 was absolutely nothing to mark its boun- 

 daries. However, by the manner in which 

 the ants ran along constantly tapping the 

 board with their antennae, hunting their way 

 and turning back into the "beaten track" 



whenever in their haste they happened to step 

 off of the course, it was presumed that the 

 roadway was recognizable through the sense 

 of smell, and what tended to confirm this 

 theory was the sinuous character of the trail. 

 While from the top to the bottom it was con- 

 fined to a single board and in no place was it 

 straight for more than a few inches, it swung 

 on long angles from margin to margin of the 

 board. These crooks and turns of their road- 

 way were followed by every ant, without 

 variation, going up or coming down, for the 

 weeks they were under observation. 



As a test of the accuracy of the conclusion 

 I rubbed a place on the wall about an inch 

 wide across the roadway with a fresh piece 

 of Spearmint chewing gum, thinking if the 

 ants were guided on their way through sensing 

 the odor of their own tracks, they would be 

 confused when they reached the spot, depend? 

 ing as I did upon the probability that the 

 pungent odor of the gum would obliterate the 

 ant odor. I chose a time for* applying the 

 gum when there were but comparatively few 

 ants working and where there was quite a 

 break in their column. Now let us see what 

 happened. When the first ants to approach 

 the spot reached a point within three-quarters 

 of an inch of the gum-scented place they 

 hesitated in their march and exhibited other 

 signs showing that they recognized that some- 

 thing had happened to their roadway. It was 

 as if they had come to a waterway where 

 their bridge had been unexpectedly carried 

 away. The ants ran along the bank, their 

 antennae working excitedly. Back and forth 

 they went, until, notwithstanding the pun- 

 gent smell of Spearmint they seemed to dis- 

 cover the narrow course that connected their 

 roadway and slowly over it they passed. If 

 the ants were actuated by sense of direction 

 only it seems to me that they would have 

 crossed the obstruction at various points; but 

 not so, the crossing was made without excep- 

 tion at the break in the trail. However, the 

 place was not found and used without con- 

 fusion and study of the situation on the part 

 of the insects. The effect of the obstruction 

 was the same upon the ants on either side. 

 All were held up here on their course 

 whether it was up or down the wall. The 

 obstruction was operative for an hour or 

 more, though after the first quarter it was 

 not so effective. Even after the first five 

 minutes some of the ants began to cross, 

 showing less hesitation and confusion. While 

 a few others ants for more than two hours 

 after were disturbed and confused to some 

 extent by the lingering scent of the Spear- 

 mint. 



