482 ANNUAL BEPORT SMITHSONIAN INSTITUTION, 1920. 



although all that we can say about the sense is that the most intelli- 

 gent insects, such as ants and bees, utilize this sensation to the best 

 advantage in rearing their young which need a warmth as gentle and 

 constant as possible. 



All insects can probably distinguish dry air from humid air. Ants 

 are very sensitive to changes of humidity in the soil, while bees 

 are always irritable and cross on very humid days. Bees can also 

 tell when a thunder shower is approaching. 



Much has. been written about the supposed sense of direction in 

 insects. Bethe calls it a mysterious force that guides bees and ants 

 back to their home. Forel strongly denies any such sense or force 

 and says that the faculty of orientation is the result of the experi- 

 ence of known senses, combined or not, especially of sight, smell, 

 and touch, according to the case and species. In aerial orientation 

 vision mostly predominates; this is well illustrated by the carrier- 

 pigeon and the honeybee, both of which remember landmarks. In 

 terrestrial orientation the sense of smell often plays a predominant 

 part, as illustrated by dogs and ants; but smell gives place to sight 

 in many animals, among which are man, monkeys, and arboreal 

 reptiles. In the orientation of subterranean and cave-dwelling 

 animals, smell and touch reign as masters. In spiders, it is touch 

 which is the principal orienting sense. 



Forel thinks that pain is much less experienced in insects than in 

 warm-blooded vertebrates. Cases could be cited showing that cer- 

 tain insects experience little or no pain at all when wounded, while 

 other cases could be cited indicating that they do experience pain; 

 nevertheless, their signs of discomfort when wounded can probably 

 be explained merely by reflex actions. On the other hand, bees with 

 mutilated antennae seem to suffer considerably and do not live long. 

 They do not bleed to death for the wounds soon heal, but appear to 

 die from effects of the shock. Since pain in the higher animals is 

 nature's indicator that something is wrong, there is no good reason 

 why the higher insects should not also experience pain. 



INTELLIGENCE OF INSECTS. 



Now as we have closed the brief discussion concerning the senses of 

 insects, let us inquire as to how well the sensory impressions have 

 been stored in the brains of insects. This subject has been much 

 debated and we find two of the chief authorities taking opposite 

 extremes. Bethe regards insects as reflex machines and does not 

 use any term which has any resemblance to anthropomorphism, 

 whereas Forel probably goes to the other extreme by attributing too 

 much to the intelligence of insects. 



