33 
THE SENSES OF INSECTS,- 
By C. V. Riley. 
Having thus dealt in a .summary way with some of the structures 
aud economies of the social insects, let us now consider their psycho- 
logical manifestations.! 
Of the five ordinary senses recognized in ourselves and most higher 
animals, insects have, beyond all doubt, the sense of sight, and there 
can be as little question 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 differ 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 larvae which are exposed more or 
less fully to the light, while those larvae which are endophytous. 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 of insects have their simple eyes 
in addition to the compound eyes. In many cases, however, the former 
are more or less covered with vestitnre, 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. 
