INSTINCTS OF HARVESTING ANTS 25 



beside their road do not in the slightest confuse them, 

 but if the finger be drawn gently across the track they 

 instantly recognize the interference, appear to have 

 lost their way, and not until a number have crossed 

 and recrossed is the orderly progress again resumed. 



I placed a strip of cardboard an inch in width 

 across the track of the harvesters. This caused intense 

 commotion, and not until many hours had elapsed did 

 the ants carry their loads over the narrow cardboard 

 strip. When the stream was restored I then removed 

 the strip and the ants were just as much confused as 

 before, although I had given them back their original 

 road. They were unable to recognize their old track, 

 since the odour had disappeared while covered with 

 the cardboard. I transferred the strip over which the 

 ants were freely moving to another track and placed 

 it down in a manner similar to the first, but the ants 

 were not now in the slightest confused ; they carried 

 their burdens without any hesitation directly across 

 the cardboard strip. In this last little experiment the 

 strip of cardboard had been given the natural scent by 

 the numbers of harvesters that had run across it on 

 the first track, and it thus became indistinguishable 

 from the usual road to the ants which hastened along 

 the second track. In the employment of camphor to 

 test the sense of smell we stimulate the pugnacity of 

 the soldiers. Camphor is a substance which the 

 harvesters dread ; from its powerful odour they dash 

 headlong away ; nevertheless, so plucky are the 

 soldiers, that I have seen one grasp a large fragment 

 of this stupefying substance in its jaws and endeavour 

 to drag it away from the nest. 



When a harvester leaves the general track in search 



