443 



Although most of the winged forms of this species leave the nests 

 in summer or early autumn, I have a note from Messrs. W. P. Flint 

 and G. E. Sanders, reporting the finding of winged females in a nest 

 at Galesburg, 111., October 29, 1909. 



II. Experiments on the Traii, Formation and Orientation oe 

 THE Common House Ant, Monomorium pharaonis L. 



The little creatures that form the subject of these experiments 

 forced themselves upon my attention by interfering seriously with my 

 regular work and making themselves a general nuisance in the lab- 

 oratory. They had a nest in some inaccessible place in the walls of 

 the building, from which they formed regular trails to any substance 

 in the laboratory, such as insect specimens, fruit, meat, sugar, etc., 

 which they found suitable for food. A piece of fruit left lying on 

 a desk in the laboratory was sure to be found by some wandering 

 worker, and in an hour or so a regular trail would be formed leading 

 to it, along which hundreds of the little workers would pass to and 

 fro in the course of a few minutes. 



For my regular experiments I was keeping in Fielde nests a num- 

 ber of colonies of the common corn-field ant, Lasius niger americanus, 

 which I often fed with sugar dissolved in water. The little M. phara- 

 onis could crawl in under the roof -panes of these nests to the food 

 provided for the Lasius colonies and many times caused the death 

 of an entire colony in a single night. I do not know just how the 

 L. americanus ants were killed. I never saw a M. pharaonis attack a 

 living worker of the former species, but in some way its presence in 

 the nests in such large numbers so irritated the corn-field ants as to 

 cause their death. I have seen workers of M. pharaonis attack a queen 

 of L. americanus that was already weakened to such an extent that 

 she was unable to right herself when lying on her back. 



The regularity of the trails, the closeness with which they were 

 followed, and the extreme sensitiveness of the ants to slight breaks 

 in their trail, made by rubbing the finger across it or placing some 

 odoriferous substance or even a small piece of clean paper upon it, 

 interested me, and induced me to perform some experiments to deter- 

 mine whether they depended entirely upon a chemical sense, located in 

 the antennae, to find their way, or whether they possessed also a sense 

 of direction. While I was working on this problem other questions of 

 a similar nature presented themselves which I tried to answer by ex- 

 periments, some of which are given below. 



