2oo THE POPULAR SCIENCE MONTHLY 



visits Croton texensis, Perdita albipennis visits Heliantlius annuus 

 (sunflower), and Perdita senecionis visits Senecio Douglasii. "It may 

 be laid down as a rule/' says Professor Cockerell, " that each species of 

 Perdita visits normally hut one species of flower, hut occasionally speci- 

 mens may be found on flowers to which normally they do not belong." 

 But in many instances several species of Perdita frequent the same 

 flower. The bees of this genus are small forms very frequently marked 

 with bright yellow. 



Many species of Colletes, Epeolus and Melissodes visit almost ex- 

 clusively the flowers of the Composite, as the thistles, golden-rods and 

 asters. Xenoglossa pruinosa confines itself to Cucurbita pepo or the 

 common field pumpkin; while Megachile campanulas, one of the leaf- 

 cutting bees, is a monotropic visitor of the bellflower Campamda ameri- 

 cana. Many other instances are recorded, and many more will no doubt 

 be discovered when our bee fauna is better known. 



This is certainly a very singular habit on the part of bees, and one 

 which could hardly have been foreseen. On the contrary, it is generally 

 supposed that bees fly about sipping sweets indiscriminately, as they are 

 so commonly represented by the poets. 



He woos the Poppy and weds the Peach, 



Inveigles Daffodilly, 

 And then like a tramp abandons each 



For the gorgeous Canada Lily. 



It is really getting unsafe for poets to write about nature in their 

 old, haphazard way, trusting chiefly to their imagination as a guide. 

 Fancy can supply nothing half so wonderful as the true facts about 

 flowers and insects. Let us consider what theories naturalists have ad- 

 vanced to explain this curious habit! 



In Kerner's day only a few oligotropic bees were known, and he be- 

 lieved that they gave the preference to certain flowers because they 

 found their odors so highly attractive. But it is incredible that so 

 many bees should be dominated in their flight to such an extent by 

 various floral odors, and besides they not infrequently visit several 

 flowers which differ in scent. No doubt, though, bees have their prefer- 

 ences in odors and nectars, and probably they prefer pollen that has 

 a roughened or spined surface to that which is smooth. 



A more probable explanation claims that female oligotropic bees 

 have adopted this method of visiting flowers to avoid competition in 

 gathering pollen for brood-rearing. This theory is only partially satis- 

 factory and certainly is not always applicable, even assuming that such 

 a partition is beneficial or required. The four species of Andrena, 

 which in this locality visit exclusively the willows, do not thus avoid 

 competition nor do they thus benefit other bees. The willow aments 

 have pollen enough for all comers. In this particular case this habit 

 seems to have arisen because it was advantageous to these bees to re- 



