PSYCHE 
VOL. XXXV. JUNE 1928 No. 2 
THE BEE THAT WORKS IN STONE; PERDITA 
OPUNTIM COCKERELL 1 
By Clarence P. Custer, 
University of Colorado, Boulder. 
Some seven miles east of Boulder, nestled at the foot of the 
Colorado Rockies, there rise some sandstone cliffs of peculiar 
interest to the biologist and the geologist. These are termed 
the White Rocks in reference to their appearance when seen at a 
distance. Around them there stretch for miles and miles the 
fertile farming lands of Boulder County. Thus the White Rocks 
are isolated from other similar rock formations; and here there 
lives a bee that has been officially reported from nowhere else 
in the world. It is Perdita opuntice Ckll . 2 
One may find this remarkable bee in the early summer, in 
the months of May and June, as it hovers and darts from flower 
to flower in its tireless search for pollen. And in this one notices 
a peculiar adaptation. Apparently it visits but one plant spe- 
cies, the bright yellow flowers of the cactus, Opuntia mesacantha 
Raf ., 3 from which it derives its name. How specially adapted 
this insect is! Not content with limitation to White Rocks, it 
must also depend on the flowers of but one kind of plant for its 
existence. 
The writer is indebted to Mr. S. A. Rohwer and Miss Grace Sandhouse. 
for the determination of specimens; to Dr. Edna Johnson for the identification 
of some plants; to Miss Helen Mowry and Miss Celia Light for assistance in 
the photography and for helpful suggestions; to Professor R. D. George for 
some geological material as well as interesting information concerning tunnel- 
ways in the rock formations of different localities; and to Mrs. B. O. Custer, 
Miss Arline Elftman and Mr. Russel Mann for assistance in the field work. 
determined by Miss Grace Sandhouse. 
determined by Dr. Edna Johnson. Synonyms are 0. humifusus 
Raf. and 0. rafinesquii Engelm. 
