196 Zoology of Colorado 



How can we explain this extraordinarily rich bee-fauna? 

 Throughout the world, it is found that dry sunny countries 

 furnish the greatest number of bees. For the most part they 

 nest in holes in the ground, and dry banks and slopes are favorable 

 for their domestic arrangements. Yet the country must possess 

 a large and varied flora, for the bees are dependent on flowers. 

 Colorado is preeminent in both these respects. The species of 

 flowering plants number over 2,500, many of them found in the 

 drier localities. Other regions especially rich in bees are New 

 Mexico, Arizona, California, Turkestan, and North Africa. The 

 deserts of Peru produce many interesting species, but the flora 

 is restricted on account of the aridity, and there are great stretches 

 of country where nothing, or practically nothing, grows. 



According to their habits, bees are said to be oligotropic or 

 polytropic, these technical terms meaning that the insect visits 

 few kinds of flowers (sometimes only one kind) or many kinds. 

 The domesticated hive bee and the bumble-bees are polytropic, 

 and to catalogue the flowers they visit is almost equivalent to 

 listing all those in bloom where and when they are flying. On 

 the other hand, there is a genus of very minute bees called Perdita. 

 all the members of which are oligotropic. When I first became 

 interested in this genus, in 1895, sixteen species were known. We 

 now know 165, and it is quite certain that many remain to be 

 discovered. The headquarters of Perdita is the North American 

 southwest, from New Mexico to California, but Colorado has 30. 

 To the south the extreme outpost is in a dry part of Guatemala, 

 where Mrs. Cockerell discovered Perdita tropicalis. To find these 

 little bees, it is only necessary to watch the various desert flowers, 

 and when small insects are observed, sweep over them with a 

 fine net. Special kinds will be obtained on such plants as sun- 

 flower, golden rod, resin-weed, croton, spurge, cleome, etc. One 

 of the most remarkable, constituting a new subgenus (Lutziella) 

 was discovered by Dr. F. E. Lutz at White Rocks, near Boulder. 

 It visits only the flowers of the prickly-pear cactus, Opuntia. 



Another classification of bees is based upon the mouth-parts, 

 the characters of the tongue, maxillary blade and palpi or feelers. 

 The more primitive bees, as they are generally understood to be, 

 have short broad bilobed tongues. It was considered that this 

 character radically separated one group from all others, until it 



