THE FLOWER AND THE BEE 



the flies dart swiftly about and poise on the wing when sucking, 

 in the same manner as the hawk-moths. 



In the Alps bee-flies were observed by Mueller to visit three 

 times as many red, violet, and blue flowers as yellow and white 

 ones. But in Wisconsin Graenicher's observations show nearly 

 the opposite result, " in other words, more than twice as many 

 white and yellow flowers have received the attention of these 

 flies as red, purple, or blue ones." In reply to an inquiry of 

 the writer's as to how he accounts for Mueller's results, he 

 replies that it may be explained by a larger number of red and 

 blue flowers in the Swiss flora than in that of Wisconsin. He 

 also calls attention to the curious fact that during seven years 

 in Germany Bomhylius discolor was observed to prefer the 

 flowers of the lungw^ort {Pulmonaria officinalis) to those of any 

 other plant, visiting other flowers only in the case of necessity. 



The dance-flies {Empididoe), which may often be seen near 

 running brooks dancing in mid-air beneath the foliage of the 

 trees, have long tongues, and resort to many flowers for nectar. 

 I shall long remember the fair June afternoon spent in collecting 

 the visitors of the twinflower {Linnoea horealis). In an open 

 grove of tall hemlocks a large bed of this trailing evergreen vine 

 was pink with nodding blossoms. (Fig. 85.) The flowers, 

 which exhale a sweet, vanilla-like fragrance, are borne in pairs 

 at the summits of elongated peduncles. The inverted position 

 of the flowers excludes the rain. The nectar is secreted at the 

 base of the corolla, on the lower side of which there is a yellow 

 marking or honey-guide. Within the corolla are many inter- 

 crossing hairs w^hich shut out small, useless flies, which I have 

 seen vainly seeking an entrance. During the afternoon I col- 

 lected eight visitors, all of which were found on examination 

 to belong to a single species of dance-fly {Empis rufescens). 

 Other observations show that this fly is the only pollinator in 



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