392 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1021. 



Wishing to establish a colony of Pseudomyrmas on our enrowinj? 

 ^4fc/r/V/ comigera in one of the greenhouses of the Department of 

 Agriculture, I wrote to Mr. J. M. Cuaron of Tampico, Mexico, ask- 

 ing him to send me a few branches of the species growing in that 

 vicinity with thorns occupied by living ants. In a few days I 

 received from him a box containing several branches of Acacia 

 sphaerocephdla. On opening it I found it swarming with belligerent 

 little ants. "Without delay I took the box to the greenhouse and 

 lodged it in the branches of our little tree. Almost immediately the 

 ants took possession. I saw one little male visit several thorns in 

 succession, vibrating its Avings and hanging on to the tip of the thorn 

 by his anterior legs, Avhile he rubbed the tip of his abdomen against 

 the thorn. The next morning I found the workers engaged in gnawing 

 holes in the thorns, invariably in a single thorn of a pair and always 

 near the tip. The following day there were two thorns thus per- 

 forated and I saw the workers carrying the larvae into one of them. 

 The ants, however, do not appear to be quite at home on their new 

 host plant, possibly because there may be a lack of food and perhaps 

 because many of the neighboring plants have been sprayed with 

 poisonous mixtures from time to time, to free them from scale insects 

 and other parasites. One thing is certain, the enlargement of the 

 acacia thorns is not wholly due to the ants, for many of the thorns 

 on my tree were quite large and hornlike before the ants had been 

 placed upon them. My experiment established the fact that the 

 little colonies in the individual thorns are not independent of one 

 another, but larvae, pupae, and ants may be transferred from one 

 thorn to the other without opposition from ants already established 

 in the new thorn. I had hoped that the ants would free the acacia 

 of certain scale insects with which it was infested, but I was dis- 

 appointed to see them passing by these insects apparently without 

 taking any notice of them. Many of the thorns are now tenanted, 

 and I am looking forward with interest to see whether my coloniza- 

 tion scheme will be a success. Plate 3 shows a pair of the thorns 

 from Mexico, which I photographed after having chloroformed the 

 ants, all of which, in the various stages, occupied the thorn photo- 

 graphed. 



That a single species or variety of Pseudomyrma is not restricted 

 in its choice of a home to trees of the same species was demonstrated 

 by the observations of Mr. Guy N". Collins in the State of Chiapas, 

 southern Mexico, where he collected several varieties of Pseiidomyrm a 

 be7f/\ but not the typical form, which is black. Most of the speci- 

 mens collected by Mr. Collins were found by Professor Wheeler to be 

 transitional forms intermediate between the dark-colored t} y pe and 

 the pale variety fulvescens, to which my Tampico specimens belong. 



