78 RECIPROCAL NUTRITIVE DISJUNCTIVE SYMBIOSIS 



are the Lepidoptera, or butterflies and moths. These are nectar 

 feeders only and their mouth parts are very greatly specialized and 

 elongated to enable them to obtain nectar from long corolla tubes. 

 The butterflies which fly during the day and visit mostly showy and 

 fragrant flowers are rather haphazard in their movements. They 

 are apt to visit several different species of flowers within a few 

 minutes and for that reason are not very efficient pollinators. Some 

 of the moths, on the other hand, especially the hawk moths, are as 

 precise in their movements as bees. The moths are night-flying 

 insects and visit mostly night-blooming flowers. The hawk moths 

 have very long mouth parts, sometimes as much as 7 or 8 cm. in 

 length, which are coiled up when not in use. They visit mostly 

 fragrant, white flowers with long corolla tubes. 



The majority of the flies are of no importance as pollinating agents. 

 The syrphid flies, however, which look a great deal like bees, feed 

 largely upon nectar and pollen and so are of considerable importance. 

 The carrion flies are also of some importance especially in connection 

 with the pollination of ill-smelling flowers. They seem to be 

 attracted particularly by odors that are offensive to human beings. 

 A few kinds of beetles sometimes effect pollination but as a rule the 

 floral visits of beetles result in more harm than good. 



49. Color, Odor and Memory in Insect Pollination.— A great deal 

 of work has been done during the past one hundred and fifty years 

 in efforts to determine the relative importance of color, form, odor 

 and memory in attracting or directing insects, especially bees, to 

 flowers, and a great deal has been WTitten on the subject. Much 

 more needs to be done before we can speak with certainty on all 

 phases of the question but certain facts are now fairly well estab- 

 lished. 



Many experiments have been performed for the purpose of de- 

 termining w^hether bees can recognize colors, such, for instance, as 

 removing the corollas of flowers, using artificial flowers, painting 

 flowers unusual colors, or enclosing flowers in glass, and then ob- 

 serving the activities of the bees. While there has been some dis- 

 agreement among different workers, the most reliable results show 

 that bees do readily distinguish colors. Honey-bees show a decided 

 preference for blue, but, when working on any particular species, 

 they show a preference for the color of that species whatever it may 

 be. It has also been shown, however, that they discriminate be- 

 tween colors only when it is of advantage to do so. In the case of a 

 species with variable colors they soon learn that color discrimination 



