5 68 
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, Ill., 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, Iris 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 nectary is found (Fig. 762). The actual pollinating visitors were 
chiefly small Andrenid bees. 
It will also be well to note, before taking up the special 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 sufficient 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 Syrphidse). The pollen collectors are mostly 
