UNIVERSITY OF CALIFORNIA 
 
 COLLEGE OF AGRICULTURE 
 
 BERKELEY, CALIFORNIA 
 
 AGRICULTURAL EXPERIMENT STATION 
 E. J. WlCKSON, Director 
 
 CIRCULAR NO. 38 
 
 (August, 1908.) 
 
 THE ARGENTINE ANT IN CALIFORNIA. 
 
 BY 
 
 C. W. WOODWOETH. 
 
 A pest that may easily prove to be the most troublesome insect ever 
 introduced into the State has been recently discovered in our midst. 
 Specimens of this insect were collected about a year ago by Mr. J. 
 
 Fig. 1. The Argentine Ant, greatly enlarged. The actual size is shown in 
 
 small figure below. 
 
 Chester Bradley, at that time an assistant in the Entomological De- 
 partment of the University of California. The species was not recog- 
 nized by him at the time as anything unusual and only within the last 
 two months lias the presence of the A r-cnl^^anl in the State been 
 
known. The identification of the insect was made by Professor W. M. 
 Wheeler of the American Museum of Natural History, to whom these 
 specimens of ants collected by Mr. Bradley had been submitted for 
 identification. Dr. Wheeler at once made known the character of the 
 insect and the writer has just returned from a trip east, where he 
 con suited with Mr. Bradley and Dr. Wheeler and then proceeded to 
 Xew Orleans and had opportunity to study the insect in that region, 
 where it has been highly injurious for a number of years. Professor 
 E. S. G. Titus, who was the representative of the United States Divi- 
 sion of Entomology to study the pest in New Orleans, has also recently 
 visited with me one of the infested areas in this State and verified the 
 insect in the laboratory and field. 
 
 The exact locality of the collection made by Mr. Bradley has not 
 been determined. It was supposed by him to be Ontario, but very 
 careful examination of the ants of that district has been made without 
 finding this species. It has been found abundantly, however, in the 
 following northern localities, East Oakland, Alameda, San Francisco, 
 San Jose, Cupertino, and a point near Campbell. In the southern part 
 of the State Prof. H. J. Quayle has just located a small colony in 
 Los Angeles and another at Azusa and a third at Upland. 
 
 The Argentine ant is primarily troublesome as a household pest, 
 but in Louisiana it has also proven of first importance in the sugar cane 
 fields, and in the orange orchards. The writer fears that, besides 
 its other injurious habits, it may not be second in importance from 
 the orange grower's standpoint to the introduction of the white fly, 
 to which attention was called by this station a year ago, and which 
 seems to be gradually spreading over the State.* Of course, there 
 is a possibility that the insect may not prove equally troublesome 
 in all parts of California on account of our peculiar climate; but, on 
 the other hand, it may prove even more troublesome than at New 
 Orleans. Indeed, Professor Newell of the. Louisiana Crop Pest Com- 
 mission, who has given more attention to a careful study of this insect 
 than any one else, expressed to me his belief that our climate would 
 be more favorable for the ant than that of Louisiana. At any rate 
 the possibility of the insect becoming a pest in California comparable 
 to the work it has already done in Louisiana should cause us to give 
 the matter the most serious consideration. 
 
 * Prof. Titus of the Utah Agricultural College and Special Agent of the U. S. 
 Division of Entomology, teUs me that while not particularly looking for the insect, 
 lie noted the presence of t^^^ T >iite Ply, Aleurodes citri, in Chico and Visalia. 
 
HISTORY IN OTHER COUNTRIES. 
 
 As the name Argentine ant suggests, the insect was first described 
 from the Argentine Republic. It is common also in Brazil and is 
 doubtless native to the southern part of South America. No one lias 
 given us an account of the seriousness of the insect in its native 
 country. The only record we have of the insect in other countries is 
 its presence in Madeira, where it was reported as long ago as 1898 to 
 have entirely displaced other species and become apparently the same 
 sort of a pest which it has proven to be about New Orleans. It was 
 noted as early as 1891 along the wharves in New Orleans, where the 
 coffee ships from Brazil were docked. By 1895 another region five or 
 six miles up the river was noticed to be infested. In 1899 they were 
 already present at Audubon Park. By 1904 Mr. Titus of the United 
 States Department of Agriculture, who was the first to give us a full 
 account of these insects, records them from many points along the 
 railroads leading out of New Orleans, as well as a large part of the 
 town. Professor Newell this year reports them as occupying fully 
 five thousand square miles of territory, extending from New Orleans 
 southward to the Gulf of Mexico ; to the north and west one hundred 
 and eighty to two hundred miles; and east beyond the boundary of 
 the State ; and wherever the insect has become abundant it has proven 
 itself by far the most troublesome species of ant, and has practically 
 driven out all other species. The spread of the species will thus be 
 seen to be rather slow, but it completely occupies all the territory it 
 infests. 
 
 RELATION TO OTHER INSECTS. 
 
 Like many other kinds of ants, the Argentine species is very much 
 attracted by the secretions of scale insects and plant lice. Every tree 
 in New Orleans and adjacent towns is continually patrolled by these 
 ants and there seems to be very good evidence that the ants care for 
 certain of these insects in much the same way as the corn root aphis 
 is cared for in the Mississippi Valley by the common ant of the corn 
 fields. At any rate, the writer has repeatedly noticed ants carrying 
 mealy bugs and other insects of this general class, and it is well known 
 that the mealy bug so injurious to sugar cane is very much worse where 
 the ant is abundant. Exactly the same habits are observable in the 
 infested districts here in California. Some of our native species of 
 ants have been justly accused of protecting the woolly aphis, and 
 probably scale insects have been defended froimtheir parasites in many 
 
instances. In this Stale, where plant lice and scale insects are naturally 
 so injurious, this tendency of the Argentine ant to care for these insects 
 may be a particularly serious feature of the situation. 
 
 Attention has already been directed to the tendency of these ants 
 to destroy other species of the same group. Many observers have noted 
 the battles of the ant in Louisiana, which invariably result in the defeat 
 of t he other species, so that the only ant now found in the houses in the 
 infested territory is this imported species. As far as our observations 
 have gone the Argentine ant completely destroys all native ants in the 
 infested regions. This is a case of replacing one bad pest by another 
 still worse. There are a few cases, however, in which the ant has been 
 somewhat of a benefit. Professor Newell tells me that one reliable 
 correspondent reports the ants as having entirely destroyed the bed 
 bugs in the poorer sections of New Orleans, and the very annoying 
 pests known in the south as chiggers have disappeared in the neigh- 
 borhood of Audubon Park, apparently on account of the presence of 
 the ant. These slight benefits, however, in no way offset the damages 
 done by this pest. 
 
 DAMAGE TO CITRUS TREES. 
 
 The direct attack of these insects upon citrus trees is a matter that 
 can not be other than of the highest importance to California growers. 
 At the Lousiana Experiment Station at Audubon Park the production 
 of oranges was entirely prevented this year through the attack of these 
 insects upon the opening blossoms, or if these escape, upon the young 
 fruit itself. It was too late in the season for me to see the method of 
 attack when I visited New Orleans, but as described to me, it consists 
 in the insect simply boring into the center of the bud and eating or 
 injuring enough of the substance to cause its destruction. This method 
 of attacking the blossoms of plants is not by any means confined to 
 oranges, since many other kinds of flowers are also attacked. The ant 
 has entirely destroyed the cut flower industry in New Orleans. In 
 some of the orchards about New Orleans numerous methods have been 
 tried to prevent the insects climbing the trees, but even as effective 
 a barrier- as tree tanglefoot has proven effective only for a day or two. 
 The insects soon cross the bands upon particles of dust or upon the 
 dead bodies of other members of the colonies. There is a possibility 
 that our method of keeping a dry mulch on the surface of the ground in 
 orchards will prevent the formation of burrows, and therefore keep 
 our orchards fairly free from the insects, but their habit of nesting 
 among the roots of trees, and that of traveling long distances may 
 enable them nevertheless to do the same injury here as in Louisiana. 
 
HOUSEHOLD PEST. 
 
 It is primarily, however, as a household pest that this insect has 
 made itself dreaded in Louisiana. No insect has ever given the people 
 of that district so much annoyance and no insect has been so hard to 
 control as the Argentine ant. It has fully maintained its reputation 
 in the infested districts here in California. Its habits are very similar 
 to those of other species, but its ceaseless wandering and small size 
 enable it to seek out every hiding place, and whenever food is found 
 they will soon be swarming in countless numbers. 
 
 The old and well-known method of placing the legs of tables in 
 dishes of water for instance is of no avail whatever against this species 
 of ants, since the slightest accumulation of dust on the surface of the 
 water furnishes a sufficient bridge over which the ant can pass. It is 
 a very general feeder, eating anything that other species of ants attack, 
 including all kinds of food materials, and both Professor Titus and 
 Professor Newell report cases where they have directly attacked infants 
 in a most distressing manner, and are capable of biting severely enough 
 to be quite a nuisance to larger human beings. 
 
 It is much more successful than any of our native species in ob- 
 taining food. Just outside of the infested district the native species 
 are normally abundant. An area which would afford foraging ground 
 for a hundred native ants is infested by fully ten thousand of the 
 Argentine species. 
 
 STORED PRODUCTS. 
 
 The Argentine ant proves very annoying in warehouses and stores, 
 as well as in residences. Every kind of food product seems to be 
 attacked by these creatures. Fruits, dry and fresh, meal, sugar, etc., 
 are all subject to attack, and the impossibility of protecting such 
 products from attack makes it unusually exasperating. 
 
 OCCURRENCE IN CALIFORNIA. 
 
 We already have numerous species of ants in this State. The 
 family to which this ant belongs is distinguished from other ants by 
 the structure of the fact, shown in figure 2. In related ants the 
 ridges near the antennae arise from the upper edge of the clypeus. 
 The most satisfactory character for identification of the Argentine ant 
 in distinguishing it from the other members of this family is the ar- 
 rangement of the teeth, shown also in figure 2. All other species have 
 some other arrangement. The Argentine bears the name Iridomyrmex 
 humilis Mayr. One other member of this genus is found in the 
 
Southern States. Other species occur in South America, in southern 
 Asia and Australia. 
 
 Mor( Information Seeded. — We are far from certain that the dis- 
 tribution of the Argentine ant is limited to the localities mentioned 
 above. It would be very desirable to know at the earliest possible 
 moment of the presence of the insect in any locality because of the 
 possibility of eradication. Eradication is possible, and has often been 
 
 2. The Argentine Ant. Face view showing the characteristic 
 arrangement of the teeth. 
 
 accomplished with a variety of insects when taken soon enough. We 
 would like to suggest, therefore, that specimens of ants of all kinds be 
 sent in to the Experiment Station for authentic determination. We 
 will be very pleased to examine and report upon all such material sent. 
 How to Send Specimens. — Specimens may be sent through the mail 
 if enclosed in any tight receptacle. We would suggest for this purpose 
 the use of an ordinary gelatin capsule. These can be obtained at any 
 drug store. The insects can be collected by wetting the finger and 
 putting it quickly over the ants, and before they can untangle them- 
 selves they can be enclosed in the capsules. Put but a single ant in 
 each capsule, but collect two or three at least of each kind. It is very 
 desirable to have a considerable number because of the danger of in- 
 dividual specimens being damaged, three or four will be amply suffi- 
 
cient. If more than one kind is collected keep them separate and 
 give the exact locality of each. The capsules may be enclosed in a 
 small box and mailed to the Entomological Department, University of 
 California. 
 
 LIFE HISTORY. 
 
 The whole life history of the Argentine ant has not yet been made 
 out. Professor Newell has given us the most complete account of these 
 insects, and has secured a splendid lot of observations which he will 
 probably publish later. As far as his studies have gone, there are only 
 three forms in the case of this species ; — the worker ant, which is the 
 one commonly found about the surface of the ground, and the only 
 one which is ordinarily observed; the queen, or female considerably 
 larger than the worker; and at certain seasons there are often a con- 
 siderable number of winged males. Young winged females also occur 
 at times in considerable numbers. These soon lose their wings and 
 become the ordinary queens. In every nest there will be found a great 
 number of ants in the early stages. The eggs and very young ants 
 are often stuck together and are handled by the worker ants en masse. 
 Before the young grubs become half-grown they will be cared for in- 
 dividually. The ants are continually tending these young, feeding 
 them from day to day, and transporting them about from one part of 
 the nest to another to maintain heat and moisture conditions most satis- 
 factorily, and when one breaks into a nest he will observe the workers 
 busy trying to rescue these young insects. When the larvae become 
 full grown they transform into a pupal stage in which the legs and 
 other appendages of the full grown insect are readily seen, but which 
 are not capable of movement. This ant does not spin a cocoon in this 
 stage as is common in many species. Finally, just before the ant 
 emerges as a perfect insect, one can observe the color of the eyes and 
 then of the rest of the body, beginning first as a pale brown, but before 
 emergence becoming almost as dark as the older ants. Previous to this 
 time the insects are almost pure white. 
 
 Xest Habits. — The Argentine ant is a persistent nest builder and 
 dius burrows everywhere. The nest, however, is not a compact affair, 
 but consists simply of burrows often isolated from each other, often 
 deserted and then re-occupied, and there is not the sharp distinction 
 between families which is observed among so many ants. Mother 
 insects may be dwelling contentedly together ; indeed, the ants of one 
 district seem to form one large family, no matter how many burrows 
 or how many separate establishments may be founded. 
 
8 
 
 Means of Distribution. — The Argentine ant seems to be continually 
 on the move. Nearly everywhere one can see long* caravans of ants 
 occupied in transporting the young from nest to nest. In this way 
 after a colony has been established in one locality it can spread through- 
 out the surrounding region, though the rate of progress of course will 
 be small. There are no data whatever to enable us to determine exactly 
 how fast they might go by this means. It is likely however that they 
 will only go fast enough to provide for increase in numbers. They will 
 be able thus to completely occupy the territory invaded and the move- 
 ment can be considered due to the need for better feeding grounds. At 
 the time of the flight of the winged insects it is possible that more rapid 
 extension might occur, but no ants are strong fliers, and it is not likely 
 that they would make such progress as might be made in a season by 
 the ordinary migrations of a prosperous colony. The distribution from 
 one colony to another distant center is doubtless always brought about 
 by artificial means. The distribution in Louisiana is very good evidence 
 along this line. The insects are found in great abundance along the 
 Mississippi River from New Orleans southward, where they were 
 evidently carried by drift wood in which they had established them- 
 selves, and in all other directions simply along the lines of the railroad. 
 The habit the insect has of constantly moving its colonies makes it 
 very easy for a colony to be transported in toto, having established 
 itself in some box of merchandise. Potted plants or even nursery stock 
 with the earth balled would be very favorable means of transportation 
 of small colonies. Its introduction to California was very likely by 
 rail, and it is likely that it will very largely follow the main lines of 
 transportation in its distribution over the State. As far as we are 
 aware, it is necessary for enough of a colony to include one queen at 
 least, to be transported into a new region in order to establish itself. 
 Because of its habits, however, it w r ould be very easy to have this 
 accomplished since the colony brought into a region would be very 
 likely to remove from the package in which it was transported and 
 establish itself in the ground in its new home. 
 
 REMEDIES FOR ANTS. 
 
 There are a great many remedies suggested and in use for the 
 control of ants. These may be classed in three categories : first, 
 destruction of colonies ; second, the interposing of barriers ; and third, 
 ant proof construction. With many species of ants the destruction 
 of a colony is not a difficult matter, the nest being a very definite 
 structure with only a few openings, and housing all of a single family. 
 
The best remedy to be used in such a case is carbon bisulfid, and a 
 small amount of this, say a teaspoonful, placed in an ordinary anl \s 
 nest, especially when the ground is not too dry, will result usually in 
 the death of the whole colony. The opening at the surface of the 
 ground should be covered tightly, and if the carbon bisulfid is effec- 
 tive, no further signs of the colony will be observed beyond a few 
 wandering individuals that were foraging at the time the carbon was 
 applied. These are relatively short-lived, and soon disappear. This 
 method is probably the best that can be followed even in the case of the 
 Argentine ant, but because of the relative great numbers of queens and 
 the innumerable openings, the difficulty of destroying these ants in 
 any region becomes very much greater than with the ordinary species. 
 Still it is probable that colonies in the ground can be destroyed in this 
 manner. Where colonies occur however in the woodwork of houses or 
 the other buildings, or in the bark or rotten places in tree trunks, as 
 is true of this species, the problem becomes very evidently still more 
 difficult, 
 
 Barrios. — Barriers consist of substances either repellent or difficult 
 of passage. Of the repellent substances, corrosive sublimate seems to 
 have been about the most effective. It is not yet known exactly why 
 such a substance should be repellent to ants, but it has proven so and 
 is fairly effective against the Argentine species. It will not be found 
 to be completely satisfactory however. Barriers across which ants 
 find difficulty in passing' are water, vaseline and tanglefoot, either of 
 which is completely effective as long as its surface remains clean; but 
 dust particles or dead bodies of other ants will in each case finally form 
 a bridge over which the insects can pass, They are, however, suffi- 
 ciently effective to be extremely useful, as a control measure and will 
 be found very efficient for our common larger species, but least effective 
 against the Argentine ant of all the ants occurring in this country. 
 
 Ant Proof Construction. — Of course this is the best solution of the 
 problem. AVhere ants cannot be eradicated all containers of food 
 material should be made ant tight in every region where ants are 
 troublesome. This is something that is quite possible even for single 
 rooms or dwelling houses, though it will require very different methods 
 from those which are in vogue in ordinary residence construction. 
 These ants do not burrow in wood but live in cracks or in rotten wood. 
 The important thing of course is to see to it that no cracks through 
 which ants can come are allowed to remain. In wooden houses this 
 can be accomplished by a free use of putty and paint, and special pro- 
 visions about the openings such as windows and doors, and by constant 
 
10 
 
 attention to any cracks that may form through the drying or warping 
 
 of the wood. In the case of warehouses the use of concrete as far as 
 possible is thoroughly to be recommended, since this is fairly free from 
 danger of cracking in a way to admit ants. The most serious difficulty 
 "in ant proof construction is the impossibility of free ventilation. 
 
 SUGGESTIONS FOR ERADICATION. 
 
 From what has been said above it will be seen that the control of 
 this species of ant is particularly difficult and it would seem therefore 
 a very wise policy at the present time, while the species has such a 
 limited distribution, to entirely eradicate it. If this is undertaken, 
 however, it should be with the appreciation of the fact that the work 
 involved is very great even for a small colony, because in eradication 
 work only the last individual queen insect is of any importance. The 
 simple reduction of numbers will not justify the effort that would be 
 put forward. 
 
 The first work that should be done towards eradication is to find 
 a practical means of limiting the spread from the existing colonies. 
 Perhaps a water barrier reinforced with oil may prove most feasible, 
 but much experimental work should at once be provided for to de- 
 termine the wisest procedure. 
 
 The next step would be naturally the attempt to destroy all the 
 nests in one of these areas. Carbon bisulfid is the most promising 
 means to use, but here again experimental work might result in the 
 discovery of more efficient means. When these two steps are success- 
 fully taken the remainder of the work is but the continuance of the 
 campaign along these lines. 
 
 HOW THIS WORK MAY BE DONE. 
 
 There is no legal authority in the State whose duties would include 
 the eradication of a household pest unless it be in those counties 
 having County Entomologists, whose duties are whatever the Super- 
 visors creating these offices direct. As a fruit pest, however, it falls 
 in the domain of the State Commissioner of Horticulture and of the 
 County Boards. The laws, however, creating these offices — while 
 granting abundant authority and originally designed to meet just such 
 emergencies — nevertheless fail to provide the necessary means and 
 facilities for investigation which must first be made when a new kind 
 of pest is introduced before effective work can be done and which 
 must accompany the work in most cases as long as it is under way. 
 
11 
 
 If anything- is to be done at all it requires therefore that public- 
 spirited citizens interest themselves in the matter and see that the 
 machinery of government by which emergencies are met be set in 
 motion. 
 
 It should be understood that the whole State is interested in this 
 matter, and not simply the communities where the insect is now present. 
 There is no reason to expect this insect to spread in this State less 
 rapidly than in Louisiana, and if that is accomplished the insect will 
 be infesting the homes of ninety percent of the population of the State 
 within ten years. If one community destroys the insects in its midst 
 it stands in continuous danger of becoming re-infested, thus necessitat- 
 ing doing the work over again. Thus far the insect is practically 
 confined to towns. For many years this was true in Louisiana. The 
 ants spread very slowly through the towns, infesting block after block, 
 coming to the towns in shipments by rail or boat and only spreading 
 into the country after completing the infestation of the towns. Now 
 they are beginning to appreciate the danger to their cane and orange 
 crops after five thousand square miles of territory are infested and the 
 insect has spread into an adjacent State. Here there is probably less 
 than five square miles of infested territory. The people in the infested 
 districts are ready and anxious to do anything that might be necessary 
 to rid themselves of the pest, but there is nothing that they can do 
 individually except little palliative measures that leaves the great 
 menace to the State at large unaffected. 
 
 If eradication is not accomplished, besides the financial losses to 
 Horticulturists, the majority of the inhabitants of the State must 
 expect in a few years at most to have hundreds of these insects patrol- 
 ing their homes from cellar to garret, day and night, winter and 
 summer.