132 COMPETITION AND CONSTANCY. 



striction of the term constancy to polytropic hymenoptera and he extended 

 it to apply to polytropic and oligotropic bees that visit but one species of 

 flower during a flight. For the honey-bee constancy is the usual rule at any 

 moment, as it is for the social bees generally, a fact shown by the pollen 

 stored up in the hives. It is likewise the rule that the pollen-baskets of 

 bumble-bees contain the pollen of a single species. The fidelity of bees in 

 general to a single species of flower is far from absolute, but it may be very 

 frequent. Within the limits of observation it appears only with respect 

 to the collection of pollen and not at all with that of nectar. Consequently, 

 it rarely exists with the males. For the same reason, doubtless, it is hardly 

 to be found in hymenoptera other than the bees. It appears to exist in 

 relation to the gathering of pollen because the larva is less tolerent to dif- 

 ferences of food than the adult (cf. also Peiez 1889, 1894.) 



Constancy in Bombus. — Wagner (1907:38) has recorded the following 

 observations which show an exceptional degree of constancy in several 

 species of Bombus. Four individuals of Bombus lapidarius made respectively 

 31, 28, 34, and 20 visits to Vicia sepium without going to other flowers, and 

 a fifth sought Lamium album exclusively. Bombus terrestris flew 15 times 

 to Dianthus carthusianorum to the neglect of Vicia, another individual 

 ignored all flowers but those of red clover, and four others paid attention 

 only to those of Scabiosa; while the last visited similarly Melampyrum 

 nemorosum. Bombus muscorum went only to Salvia pratensis on one day, 

 in spite of the presence of Melampyrum, while on the next it flew back and 

 forth from Trifolium to Melampyrum. For a whole day Bombus terrestris 

 and silvarum worked only on species of lilac-colored flowers, ignoring all 

 others. As a result of his study of the detailed path followed by the 

 bumble-bees in these and other visits, Wagner reached the conclusion that 

 at a certain distance they are guided to flowers by vision exclusively, the 

 distance at which the species can be discriminated being determined by the 

 size of the flower, the inflorescence, or the plant group itself. 



Lovell's conclusions. — Lovell (1914:202) reaches the following con- 

 clusions as to the various types of constancy: 



"There are still in existence many intermediate stages between mono-tropic, oligo- 

 tropic 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 exceptions 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 evident 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. 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 advantage 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. As the honey-bee for a time restricts its visits to 



