316 Field, Forest, and Wayside Flowers 
courage these many flies, without deterring those 
useful and desired visitors, the bees. Will flies 
learn after a while to shun the milkweed's dan- 
gerous sweets, so that they may all be left for 
worthier and more welcome guests? And how 
many generations will it take this proverbially 
foolish insect to lay the lesson to heart? (Fig. 88). 
