'30 Chapter I. 



large, heavy dung-beetle (Geotrupes typhoeus) ; or a 

 number of them are hauling to the nest a large beam 

 to our eyes it is but a broken twig which is more 

 than fifty times the weight of any single ant ! Some 

 pull in front, others push from behind, and even if the 

 latter for a few seconds pull in the wrong direction, 

 they soon notice it, and off it goes in the right direction 

 to the nest. On April 25, 1897, I observed in the 

 neighborhood of a pratensis nest near Exaten, two 

 workers dragging together a beetle of the genus 

 Calathus towards their hill; they went at a double- 

 quick, without hindrance on either side, both ants run- 

 ning backwards with equal speed. 



The mode of acting in concert is different with 

 different species of ants. Among our Formica species 

 it reaches its highest degree of development with the 

 hill ants (F. rufa and pratensis), the initiative of the 

 single ants bearing rather a secondary part. The 

 sanguine slavemaker (F. sanguined), however, which 

 is able to proceed unitis z'iribus wherever it seems suit- 

 able, combines with this power a remarkable degree 

 of individual initiative, similar to that noticed in dogs, 

 apes, and other higher animals. 



It is of special interest to watch the co-operation 

 and division of labor of different species in mixed 

 colonies of ants. In my above mentioned observation- 

 nest, which contains besides F. sanguinea four other 

 Formica species as auxiliaries, these five species have 

 divided the work necessary for the welfare of the 

 community, so as to give each species exactly the share 

 corresponding most to its instinctive preferences. This 

 division of labor, however, is neither mechanically 



