NATURAL ENEMIKS OF THE ARGENTINE ANT 

 IRIDOMYRMEX HUMILIS MAYR. 



By Charles William Mallv, M.Sc, F.E.S., F.L.S. 



The excessive abundance of the Argentine ant, [ridomyrmex 

 humilis Mayr.. in the south-western portion of the Cape Pro- 

 vince. Union of South Africa, attracts a great deal of attention 

 din-ing the summer months, and not infrequently the question of 

 controlling it b\' means of natural enemies is raised. It may be 

 as well, therefore, to give a brief summary of what is known in 

 regard to its natural enemies, and to make suggestions with a 

 view to stimulating observation on tlie subject in countries where 

 it occurs. 



In his studies of this ant in the southern United States, Mr. 

 \\ ilmon Newell came to the conclusion that it was an introduced 

 species, and that the available evidence pointed to Argentina as 

 the place where the species originated, and he therefore proposed 

 the popular name " Argentine Ant." In regard to nattiral 

 enemies. Mr. Newell found that, in the southern United States, 



the Argentine ant is remarkably free from natural enemies, and very few 

 of these have been noted during the course of our investigations, while 

 even these few are of little importance. No true parasites of this ant 

 have been observed, and apparently the only enemies are predatory 

 ones. 



■ An immature specimen of the cockroach. Thyrsocera cincta 

 Burm.. was observed by Mr. Harper Dean to capttu^e and eat 

 workers of this ant. and later on Newell observed the same habit 

 in individuals of this species- Newell also records " a jumping 

 spider" (Attidte) and variotis species of the cobweb-weavers 

 (Theridiidse) as enemies of the ant. The latter were troublesome 

 in connection with artificial colonies of the ants kept for the 

 purpose of observation. Theridium tepidarinntrn being the most 

 abundant ; but none of these spiders were observed to attack the 

 ants in otitdoor colonies. Amongst birds. Mr. G. A. Rtmner 

 observed an English sparrow picking up Argentine ant workers. 

 Newell often observed the flicker, or yellow-hammer. Colaptes 

 auratits, " industriously digging up shallow ant nests in lawns 

 and grass plots." and he considers it " the most im]x>rtant natural 

 enemy which this ant has in the Sotith." 



That the natural enemies above referred to are of little tise 

 is shown by the fact that in the opening paragraph of the report 

 by Messrs. Newell and Barber.* from which the above qtiotations 

 are made, the Argentine ant is designated as " the first among 

 the Formicid?e to attain the front rank among injurious insects 

 in the United States." 



Following Newell's conclusicMi that this ant originated in 

 Argentina, Mr. Chas. P. Lounsbury, while Government Entomo- 

 logist for the Colony of the Cape of Good Hope, made inquiry 



*Bull. 122, Bureau of Entomology. U.S. Dept- of Agri., Washington. 

 D.C. (I9T3) 



