INTELLIGENCE IX INSECTS 205 



"mere instinct" will not account. In most cases there 

 has been no previous study of the animal's behavior with a 

 view to ascertaining the nature and limitations of its instinc- 

 tive performances. Ants are observed to build bridges over 

 water or other substances which they are desirous of crossing, 

 by bringing grains of sand or bits of earth and dropping them 

 until they can effect a passage. The ants are then credited 

 with ingenuity, reason, imagination and other mental 

 qualities which human beings would employ to overcome a 

 similar difficulty. And taken by themselves the facts 

 seem to justify such conclusions. Light on the matter, 

 however, is thrown, as in so many other cases, by a study of 

 the creature's instincts, which shows that the apparent feat 

 of engineering is the result of an instinctive propensity of the 

 ant, slightly modified perhaps to meet the particular occasion. 

 Wasmann, in an instructive experiment, placed on the 

 nest of Formica sanguinea a watch glass filled with water 

 in the center of which was a sort of island on which were 

 isolated a few pupa?. The ants brought sand and threw 

 it into the watch glass until they had formed a passage way 

 to the pupa?, which were then carried away. Ingenuity, 

 surely, one is tempted to say! But the next experiment 

 inspires caution. A watch glass with no island and no pupa3 

 was placed hi the nest. This was filled like the previous one. 

 At least one important factor in the ants' activities is the 

 instinct to cover offending objects which cannot be removed 

 an instinct analagous to that of bees, which leads them to 

 cover over with propolis objects too large to remove from the 

 hive. If a dog performed similar actions in endeavoring to 

 reach an object otherwise inaccessible we should be justified 

 in attributing to the animal a considerable degree of intelli- 

 gence. Some intelligence may have been involved in the 

 behavior of the ants, but not necessarily more than a very 



