2o2 THE POPULAR SCIENCE MONTHLY 



species of Panurginus, Perdita and Andrena. These bees have a weak 

 flight and are not fitted to travel long distances. It is known that in 

 some instances they build their nests near the flowers they visit. Prob- 

 ably this generally true. The medium-sized oligotropic bees, belong- 

 ing to the genera Colletes, Epeolus and Melissodes, fly in the fall and 

 visit chiefly the Compositae, a family which offers a wide choice of flow- 

 ers. It is not always easy here to draw the line between an oligotropic 

 and a polytropic bee. 



There are still in existence many intermediate stages betwe n 

 monotropic, oligotropic and polytropic bees. While many bees visit a 

 great variety of flowers, others visit only one family, as the Compositae 

 or Nymphaeaceae, others only a single genus, as Salix, and others only 

 a single species, as the violet, strawberry or spring-beauty. Many ex- 

 ceptions no doubt occur and will be recorded when the habits of these 

 bees have been more carefully observed. For instance, I have often seen 

 the loosestrife bee on the umbels of the prickly sarsaparilla. It is evi- 

 dent that if a monotropic bee extends into a region, where the flower it 

 visits elsewhere does not occur, it must of necessity visit other flowers. 

 Dr. Graenicher writes me that the pickerel-weed bee (Halictoidcs novce- 

 anglice) is found in Wisconsin ; but the pickerel-weed does not flourish 

 in the same locality, and so this bee is compelled to visit the blossoms 

 of other plants. Evidently this habit did not originally exist among 

 bees, but has gradually been acquired. 



We may sum up the matter as follows. All bees including the 

 honey-bee show a strong tendency in collecting both nectar and pollen 

 to be constant to one species of flower. This is manifestly for the ad- 

 vantage of both insects and flowers. In the case of a number of bees 

 flying for only a small part of the season this habit has become so 

 specialized that they visit only one or a few allied species of flowers, 

 which offer an abundance of pollen and nectar. Primarily it seems to 

 be the direct advantage gained rather than the avoidance of competi- 

 tion that has led to the rise of the oligotropic habit. As the honey-bee 

 for a time restricts its visits to the white clover, so in like manner a 

 monotropic bee visits but a single kind of flower. But in the former 

 case the bee flies throughout the whole season, but in the latter when 

 the flower fades the bee's period of flight is over. 



The idiosyncrasies of bees in visiting flowers present many remark- 

 able peculiarities, and undoubtedly offer an attractive field for observa- 

 tion. There are certain bees, which though they are not oligotropic ob- 

 tain the larger part of their supplies from comparatively few flowers, 

 as the plums, thornbushes, cornels and Viburnums. In this locality 

 one of the leaf-cutting bees (Megachile melanophcra) shows a decided 

 preference for the purple vetch (Vicia cracca), and if I desired a speci- 

 men I should look for it on the blossoms of this plant. As the para- 

 sitic bees do not provide stores for their brood and seek nectar for them- 

 selves alone, they show little preference for special flowers. For a simi- 



