ENGINEERING METHODS 



bracken a large, coarse fern that overhangs them, and 

 at times almost hides them from passers-by, as a forest 

 might hide a castle standing in its midst. 



My attention was especially attracted to the character 

 of the roads leading from the ant-hills to various points 

 in the surrounding wood. These were distinctly marked 

 upon the surface of the ground, having in places a width 

 of from two to four inches stained dark brown or black 

 by the formic acid exuded from the insects as they 

 passed along. The fallen leaves and crushed grass 

 upon which the trails were made were pressed down 

 and smoothed by the constant action of innumerable 

 legs upon the surface. So well marked were these 

 trails that they were easily traced even without the 

 presence of the columns of ants that marched back and 

 forth upon them. 



While following up one of these roads, I was struck 

 by the fact that it showed scarcely any deviation from 

 a straight line. In order to test this matter more care- 

 fully, I selected a large mound from which three roads 

 radiated. These were all traced to their termination at 

 three several oak-trees, up which the columns of ants 

 ascended to obtain the honey-dew supplied by numerous 

 aphides that infested the branches. The roads were 

 carefully marked out by stakes set at short intervals, 

 a plan made necessary by the high bracken, whose stalks 

 stood so closely together that they had to be pushed aside 

 to trace the roads. 



The following facts resulted; Road No. 1 was sixty- 

 five feet in an almost perfectly straight line from the 

 nest to the tree. Road No. 2 was seventv feet long and 



/ c> 



varied less than three inches from a direct line drawn 



from the nest to a point within two feet of the terminal 



59 



