336 PROCEEDINGS OF THE ACADEMY OF [1887. 



Formica rvfa of Great Britain. While visiting the Trosachs of 

 Scotkind he found a number of nests of this species scattered through- 

 out the glen known as the Pass of Achray through which flows the 

 little Achray River, "the stream that joins Loch Katrine to Achray." 

 These nests are found on either side of the foot-walk which leads 

 from the Trosachs glen to "the sluices," as they are popularly called, 

 which regulate the stage of water in Loch Katrine. 



1. Structure of the Ant Hills The mounds raised by the Rufous 

 ants are heaps of earth intermingled with chippage of various sorts; 

 they rise to the height of about three feet, and some of them are six 

 or seven feet in diameter across the base. They stand amid the 

 tall bracken which overhangs them, and at times almost conceals 

 them from the passer by. The surface of the mounds is covered with 

 bits of straw and leaves, stalks of grass and ferns and various 

 material of like sort which forms a quite decided thatch. ISTumbers 

 of openings appear upon the surface at irregular intervals from the 

 summit to the base, and in the afternoon at 4 o'clock the workers in 

 vast numbers were dragging the chippage back and forth apparently 

 engaged in closing the doors for the night, although time did 

 not permit an observation of the actual closure. 



2. Character of Roads and Engineering Skill. That which es- 

 pecially attracted Dr. McCook's attention was the character of the 

 roads leading from the ant hills to the various points in the sur- 

 rounding woods. These roads or trails were distinctly marked upon 

 the surface of the ground, having in places a width of from two to 

 four inches which was stained a dark brown or black, probably by 

 the formic acid exuded from the insects; the leaves and grass upon 

 which the trail was made were pressed down and smoothed by 

 the constant action of innumerable legs upon the surface. So well 

 marked were the trails that even without the presence of the columns 

 of insects that thronged back and forth upon them, they were dis- 

 tinctly and easily traced. While following up one of these roads 

 the observer was impressed by the flict that it showed scarcely any 

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

 fully, he 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 in search of food supj^ly 

 from numerous aphides which infested the bi*anches of the trees. 

 The ant roads were then carefully marked out by stakes stationed 

 at short intervals, a course which was made necessary by the fact 

 that they were carried for considerable distances beneath the tall 

 bracken, wliich had to be pushed aside in order to reveal them. 

 The result of his observations is as follows: 



Road No. 1 was 21 paces in length (about 65 feet) and was 

 carried in an almost perfectly straight line from the nest to the 

 terminal tree. Ko. 2 was 23 paces in length, (about 70 feet). It 

 varied less than three inches from a direct line measuring from the 

 nest to a point within two feet of the terminal tree. There the 



