294 . MB. A. E. WALLACE ON INDIAN ETC. 



P. megacepTiala has two distinct sets of workers, which differ struc- 

 turally ; and each of these presents remarkable differences of size, 

 the small workers having a larger and a smaller form, while the 

 large ones exist of four distinct sizes ; so that in this one spe- 

 cies we have a series of individuals of six distinct sizes, which 

 differ so greatly that I am sure I am under the mark when I say 

 that it would take one hundred of the smallest to equal in bulk 

 one of the largest. This species was taken under bark, and was 

 also found in Celebes travelling across a roadway in the forest ; 

 and here the large and small individuals Avere obtained together. 



In the last-named species, though the head is rather dispro- 

 portionately increased, it is the wliole body of the insect which 

 presents such a striking difference of bulk. In P. notabilis, how- 

 ever, while the body and abdomen of the large worker are only 

 slightly increased, the head is most enormously developed, as 

 shown by Mr. Smith's figure (Journ. Linn. Soc. Zool. vol. v. pi. 1. 

 f. 3). This species was also taken crossing a pathway in the forest. 

 JB.pabulator combines these differences, the larger worker having 

 an excessively large head as well as a much larger body. The 

 large head of these insects renders them sluggish and incapable of 

 keeping up with the more active small workers ; and I observed 

 that half a dozen of the latter often surrounded those of the 

 largest size and dragged them along, as if they were fatigued or 

 wounded soldiers. This fact of the helplessness of these giant 

 ants, and their very often having smooth toothless jaws, renders 

 Mr. Bates's explanation of their probable function in the colony 

 highly probable, viz. that they serve as mere baits to ant-eating 

 animals, being naturally attacked and often carried off" first, and 

 thus allowing the working portion of the community to escape 

 destruction. Another species, P. plagiaria, is small, but very 

 active and voracious, and the large worker is only about twice as 

 large as the small one. I observed them once plundering a 

 white-ant's nest in a rotten tree, down which they were proceed- 

 ing in a continual stream, carrying away the soft and helpless 

 Termites. On anotlier occasion tliey liad discovered a large 

 Coleopterous larva {Passalus, sp.), and hundreds were engaged 

 in dragging him out of his abode in a rotten stump. 



The genus Solenopsis very much resembles the last, but the 

 species are generally red instead of brown or black. S. cepha- 

 lotes is one of the most abundant ants in the Moluccas, and is 

 the most terrible pest. It forms its colonies under ground, en- 



