568 



Insects and Flowers 



hopelessly entangled small insects on the tall sticky stem of a single Salpo- 

 glossus plant. But sometimes the burglars are successful. Needham, in a 

 careful study of the insect visitors on the blue flag (Iris versicolor) near Lake 

 Forest, 111., found a dozen or more successful pollen and nectar thieves 

 among them, while several other would-be thieves were deceived by the 

 curious markings of the flower as to the proper entrance and so failed to 



Fig. 762. — Blue flag, /ri'i sp., being robbed of nectar by skipper-butterfly; at left diagram 

 showing position of butterfly's proboscis (represented by the arrow) with reference 

 to openings of the nectaries. (After Needham; natural size.) 



make entry and get to the stores. The most persistent nectar thieves were 

 several species of Pamphilas (skipper-butterflies) which stood outside the 

 flower and inserted the proboscis obliquely between the sepal and the base 

 of the style, plying and thrusting with it until one of the two holes leading 

 to the nectar}' is found (Fig. 762). The actual pollinating visitors were 

 chiefly small Andrenid bees. 



It will also be well to note, before taking up the ."ipecial examples to be 

 described, the general character of the modifications which have arisen 

 among the regular visitors whose advantage in the way of getting food sup- 

 plies of nectar and pollen has been suflicient to impose, on some of them 

 at least, very considerable adaptive structural changes. The great majority 

 of nectar-drinking insects are bees, moths, and butterflies and two-winged 

 flies (of these especially the Syrphida;). The pollen collectors are mostly 



