340 ^"^ ANIMAL KINGDOM 



critical factor has turned out to be whether or not the stimulus used was 

 an appropriate cue for the situation. Kupelweiser stated in 1913 that 

 bees were colorblind. Discovering that captured bees released in a dark 

 room invariably flew to windows, he performed a variety of excellent 

 experiments in which bees could choose between two windows of vary- 

 ing brightness and color. He showed without a doubt that only bright- 

 ness is involved in the choice. The same year, however, von Frisch did 

 his classic experiments on color vision in bees, using groups of colored 

 cards some of which had syrup. He found proof of good color vision, in 

 which what we call orange, yellow and green were seen as one color, 

 blue-green another, blue and violet a third, and ultraviolet a fourth. 



These two sets of experiments are not contradictory. Both have 

 been repeated successfully. They illustrate that in its escape reactions the 

 bee uses only brightness cues, whereas in jeeding it uses color cues. 

 Man is handicapped to the extent that he cannot ignore color in an 

 attempt to evaluate brightness. Ordinarily man does very poorly in 

 judging the relative brightness of dissimilar colors. 



Color vision has now been demonstrated in a wide variety of in- 

 sects and crustaceans. Even the tiny daphnia with a single compound 

 eye distinguishes between orange-yellow-green and blue-green-blue- 

 violet. Probably most compoinid eyes distinguish color. Butterflies, as a 

 final example, are easily trained to feed at blue or yellow cards among 

 other colors and grays, but cannot be trained to visit green. The con- 

 clusion that they cannot distinguish green is shown to be false by the 

 demonstration that, when laying eggs, they visit only green cards. 



1 54. Behavior 



The activities of arthropods are a source of endless fascination. Be- 

 cause many of their responses are inherited as patterns that follow auto- 

 matically upon the presentation of appropriate stimuli, the behavior 

 of arthropods has been analyzed more successfully than that of most 

 organisms. To be sure most of their activities are only partially pre- 

 dictable, but nevertheless a variety of basic patterns have been recog- 

 nized. 



The simplest effect a stimulus can have upon an organism is 

 kinesis, an increase in activity. Light, for example, has a kinetic effect 

 on many diurnal animals. Povdtrymen use this as a means of increasing 

 egg production. Many arthropods become inactive in the dark (i.e., 

 "go to sleep"), moving about only in the light and at rates related to 

 the intensity of the light. The evidence of this relationship reaches a 

 dramatic level in some butterflies and diurnal moths. The hummingbird 

 moth flies only in light, and if flying in a room imder artificial light 

 will fall instantly to the floor when the light is turned off. Temperature 

 and humidity are other stimuli that may influence kinesis. Pill bugs 

 (terrestrial isopods) cannot survive low humidities, and respond to dry 

 air by restless movement. They come out to feed at night, spending the 

 day beneath objects. If they should happen to crawl beneath a stone 

 where it is dry they are unable to rest, and eventually crawl out even 



