NOCTURNAL OR HAWK-MOTH FLOWERS 



Pronuba is unique among all the thousands of moths and butter- 

 flies in the world in that she has maxillary tentacles for col- 

 lecting pollen, and a horny ovipositor for piercing succulent 

 tissue. In the collection of pollen she resembles the bees, and 

 in the manner of laying her eggs the ichneumon-flies — both 

 hymenopterous insects. 



The most widely cultivated and best-known species of 

 yucca is Adam's needle, or Spanish bayonet (Y. filamentom), 

 which is pollinated by Pronuba yuccasella. Soon after twilight 

 falls these little white moths fly from flower to flower gathering 

 from the anthers with their trunk-like tentacles, which are 

 covered with short spines, the sticky masses of pollen, until a 

 ball, sometimes twice or three times as large as her head, has 

 been accumulated. Then she usually flies away to another 

 plant, and alighting on the seed-pod pierces the wall with her 

 saw-like ovipositor and deposits an egg in one of the rows of 

 ovules. After 3 or 4 eggs have thus been laid the moth as- 

 cends to the top of the pistil, and in the funnel formed by 

 the stigmas, which are receptive only on the inner surface, 

 she crowds the ball of pollen. Apparently she intentionally 

 pollinates the flowers, for if she failed to perform this service 

 no seed would be produced and her offspring would })erish for 

 want of food. The moth herself receives no direct benefit since 

 her tongue has lost its sucking function and she no longer takes 

 food. (Fig. 67.) 



The possession of an ovipositor and spined tentacles by a 

 genus of moths, and the collection and placing of pollen on the 

 stigmas are structures and functions which stand alone in the 

 history of flower-pollination. While it seems incredible that 

 Pronuba can understand that unless pollen is placed on the 

 stigmas no seed will be produced, the more her behavior is 

 investigated the stronger becomes the evidence that such is the 



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