448 ECOLOGY 



are showy odorless flowers. The readiness with which flies are drawn 

 to sources of nauseous odors is well known, and they frequent ill-smelling 

 flowers in a similar fashion. Hawk moths have been found to be able 

 to detect at a distance of several meters the presence of fragrant but in- 

 visible nocturnal flowers, and bees have been seen to fly directly toward 

 honey artificially hidden. Indeed, there are reasons for believing that 

 many insects are able to detect odors that are inappreciable to human 

 nostrils. 



The possession of a keen sense of color is much less certain. Even the 

 ardent supporters of the " signal " theory hardly postulate it except for 

 the more specialized insects, such as butterflies and bees. The best ex- 

 periments indicate that insects are very short-sighted, none being able to 

 see distinctly for more than sixty centimeters, and bees very much less 

 than that. Objects in strong contrast (such as large light and dark 

 bodies in juxtaposition, or bodies in motion) appear to be seen rruch 

 farther than are other objects, certain Lepidoptera seeming to be ible 

 to see thus vaguely for a meter and a half, and bees for a half meter. 

 The only insects in which color perception has been definitely demon- 

 strated are the honeybees (Apis). These highly organized insects often 

 have been seen to visit gaudy but nectarless artificial flowers, and some- 

 times they attempt to get at showy natural flowers that are under glass. 

 Frequently they visit colored, unopened buds and wilted flowers, the 

 latter being at times approached, even after they have fallen to the ground. 

 Apiarists rather generally believe that honeybees are able to perceive 

 color differences, and hence they sometimes paint their hives in different 

 colors, so as to aid the bees in recognizing their abode. To the extent 

 that color is perceived by insects, it is a much more reliable " signal " 

 than odor, since the latter often is affected by the wind or masked by 

 other odors. Probably the characteristic forms of flowers serve as in- 

 dices to nectar, especially in the case of flowers that are conspicuous 

 by their shape or by their size; some observers think that form is 

 even more important than color as an insect " signal." 



Some investigators believe that honeybees not only perceive colors, but that they 

 have marked color preferences. Experiments with honey on colored papers seem 

 to show that bees tend to visit a particular color, even if others are more conveniently 

 situated, and elaborate theories have been worked out on the assumption that bees 

 dislike yellow and prefer blue, whence it seems to some observers an easy postulate 

 that the day of yellow flowers is waning and that of blue flowers is in the ascendant. 

 Such conclusions certainly are unwarranted. The constancy of the honeybee to 



