CARNIVOROUS ANTS 45 



Myrmecocystus setipes is a sturdy active species 

 much larger and more ferocious than the harvesters. 

 It is dark red in colour, sparsely clothed in a few 

 scattered hairs. Its head is large and strong, furnished 

 with powerful jaws that are armed with curved 

 pointed teeth suited to its predaceous nature. A 

 narrow neck divides the head from an elongated 

 thorax which supports the six dark slender legs and 

 ends behind in a black conspicuous abdomen. A 

 distinct difference in size exists amongst the workers 

 of a single nest. The larger individuals generally 

 reach about half an inch in length, while the smaller 

 ones scarcely exceed three-eighths of an inch ; and 

 all gradations in size are found between the two 

 extremes (see Plate, p. 13). 



It is a predaceous ant, existing chiefly on other 

 insects, while the harvesters are peaceful husbandmen. 

 The harvesters move slowly, regularly and methodic- 

 ally along definite roads, but this carnivorous ant is 

 extraordinarily active, and runs about in every 

 direction with darting agile motions well suited to 

 its predaceous habits. The smallest workers are 

 exceptionally active, and take great pains to keep 

 the entrance to the nest smooth and clean by con- 

 tinually digging in the earth with their front legs, 

 shovelling up the larger granules and carrying them 

 away in their mandibles. 



A community of harvesters contains thousands of 

 individuals, but the number in the nest of Myrme- 

 cocystus probably does not exceed more than about 

 thirty or forty members. Though possessing fewer 

 workers than the harvesters, the excavation of the 

 nest is by no means a slow process. The ants, by 



