PEKFECT SOCIETIES OF INSECTS. 



43 



twice, the size of the small ones.) All were equally engaged 

 in the labours of the colony. Large workers were also 

 noticed by M. P. Huber in the nests of Polyergus rufescens 1 , 

 but he could not ascertain their office. More light, however, 

 has been of late thrown on this subject by the observations of 

 M. Lacordaire and M. Lund upon these large workers, as 

 they occur in the nests of South American ants. They have 

 ascertained them to be strictly the soldiers, which, though of 

 a different origin, like those of the Termites before described, 

 have it expressly in charge to defend the rest of the com- 

 munity ; for which office their size — full twice that of the 

 other workers — and their immense heads and jaws in pro- 

 portion, admirably adapt them. M. Lacordaire informs us 

 that, both in Cayenne and Brazil, he has been a thousand 

 times witness of the accuracy of the facts stated by M. Lund 

 as to the military office of these large and big-headed workers 

 of Atta cephalotes, and allied species, during the marches and 

 excursions undertaken by the society. They never mix 

 themselves with the mass of the moving columns ; but, sta- 

 tioned on their flanks, they are seen sometimes to march 

 forward; then to return and halt a moment, as if to observe 

 the troop defile before them; traversing its ranks; hastening 

 to any point where their presence seems necessary, especially 

 if it have met with any obstacle on its route ; and even climb- 

 ing, as M. Lacordaire has often witnessed, up the adjoining 

 plants, and, perched on the margin of a leaf, surveying its 

 passage from this elevated position. 2 M. Lund observed four 

 of these large-headed neuters of a Brazilian species of Myrmica 

 to guard the entrance to their nest, and others attending the 

 column while on march, and hastening to the spot and alarming 

 their comrades when some of the ants were purposely killed. 3 

 An equally singular modification of form and function 

 takes place in the neuters of a Mexican ant — Myrmecocystus 



1 M. Huber calls this an apterous female ; yet he could not discover that 

 they laid eggs ; and he owns that they more nearly resembled the workers than 

 the females, and that he should have considered them as such, had he seen them 

 mix with them in their excursions. — Huber, p. 251. 



2 Lacordaire, Introd. a VEntom. ii. 498. 



3 Lund in Ann. des Sciences Nat. xxiii. 113.; quoted by Lacordaire, ubi supr. 

 and Westwood, Mod. Class, ii. 225. 



