33 



THE SENSES OF INSECTS.* 



By C. V. Riley. 



Having thus dealt iu a summary way with some of the structures 

 aud economies of the social insects, let us now consider their i)sycho- 

 logical manifestations.t 



Of the five ordinary senses recognized in ourselves and most liigher 

 animals, insects have, beyond all doubt, the sense of sight, and there 

 can be as little (juestion that they possess the senses of touch, taste, 

 smell, and hearing. Yet, save, perhaps, that of touch, none of these 

 senses, as possessed by insects, can be strictly compared with our own, 

 while there is the best of evidence that insects possess other senses 

 which we do not, and that they have sense organs with which we have 

 none to compare. He who tries to comprehend the mechanism of our 

 own senses — the manner in which the subtler sensations are conveyed 

 to the brain — will realize how little we know thereof after all that has 

 been written. It is not to be wondered at, therefore, that authors 

 should diifer as to the nature of many of the sense organs of insects, 

 or that there should be little or no absolute knowledge of the manner 

 in which the senses act upon them. The solution of psychical problems 

 may never, indeed, be obtained, so infinitely minute are the ultimate 

 atoms of matter; and those who have given most attention to the sub- 

 ject must echo the sentiment of Lubbock, that the principal impres- 

 sion which the more recent works on the intelligence and senses of ani- 

 mals leave on the mind is that we know very little, indeed, on the sub- 

 ject. We can but empirically observe and experiment and draw con- 

 clusions from well attested results. 



Sight. — Taking first the sense of sight, much has been written as to 

 the picture which the compound eye of insects produces upon the 

 brain or upon the nerve centers. Most insects which undergo complete 

 metamorphoses possess in their adolescent states simple eyes or ocelli, 

 and sometimes groups of them of varying size and in varying situa- 

 tions. It is difficult, if not impossible, to demonstrate experimentally 

 their efficiency as organs of sight; the probabilities are that they give 

 but the faintest impressions, but otherwise act as do our own. The 

 fact that they are possessed only by larviie which are exj^osed more or 

 less fully to the light, while those larvai which are eudoijhytous, or 

 otherwise hidden from light, generally lack them, is in itself proof that 

 they perform the ordinary functions of sight, however low in degree. 

 In the imago state the great majority o^ insects have their simple eyes 

 iu addition to the compound eyes. In many cases, however, the former 

 are more or less covered with vestiture, which is another evidence 



'From an address on Social Insects, as president of the Biological Society of 

 Washington, delivered in the hall of Columbian University, January 29, 1894. 

 tSee article by writer in Insect Life, vol. vi, pp. 350-360. 



