CHAPTER X 

 FLY-FLOWERS 



THAT the physical characters of flower- visiting insects, 

 such as size and the length of the tongue, should influ- 

 ence the structure of flowers would be expected; but it 

 is more surprising to find their mental traits also reflected. 

 How different is the reception accorded by flowers to many 

 stupid flies from that given to bees! Notice how the con- 

 stant and observant bees are offered nectar, pollen, shelter, an 

 alighting-platform, bright hues, and sweet odors, while unde- 

 sirable guests are excluded. But for the unspeciahzed, stupid 

 flies there are pitfall-flowers, prison-flowers, pinch-trap flowers, 

 and flowers with deceptive nectaries, deceptive colors and 

 odors. In her readiness to take advantage of their weakness 

 Nature simulates the worse qualities of humanity, although, 

 more strictly speaking, it is their inability to learn from observa- 

 tion that has induced the development of these peculiar forms. 

 But not aU flies are stupid. This is far from true of the syrphid 

 or hover flies and the bee-flies which visit nearly the same 

 flowers as do the bees. 



Their numbers and activity probably entitle the flies to rank 

 after the bees and before the butterflies and moths as flower- 

 pollinators. Mueller places them next to the Hymenoptera, 

 except in the case of the Alpine flora, where butterflies are very 

 abundant. In New Zealand both bees and butterflies are very 

 scarce, and Thomson considers the flies as the chief agents in 

 poUination. 



There are in North America more than 8,000 described species 

 of two-winged flies, or Diptera. Very many of them live largely 



160 



