236 SEVENTEENTH Report STATE ENTOMOLOGIST OF MINNESOTA—1918 
“each species of Psithyrus resembling the bumble bee with which it 
usually lives.” Since the genus only appropriates a portion of the 
food supply of its host, it may be re- 
garded as a messmate or “commensal” 
and not a parasite, though sometimes 
destructive. 
In observations made on the habits 
of this bee, it has been observed that 
it is not as industrious as the bumble 
bee, only leaving the nest somewhat 
before noon and returning toward 
evening, and sometimes passing en- 
tire days in the nest, consuming the 
honey of its host. Since this “board- 
er’ is much larger than its host, and 
consumes a large amount of honey, 
Fig. 125. Psithyrus ashtoni P . : 
: edaa eaale: y the number of bumble bees raised in 
an infested nest is naturally reduced. 
The following species are found in Minnesota either present in 
our collection, or on record as occurring here: Bombias auricomus Rob., 
B. separatus Cress., (col. plate 3), B. rufocinctus Cress., Bremus bor- 
ealis Kirby, (col. plate 3), B. fervidus F., B. pennsylvanicus Deg. 
B. affinis Cress., B. terricola Kirby, B. impatiens Harris, B. perplexrus 
Cress., B. vagans Sm., B. ternarius Say. (col. plate 3), Psithyrus 
ashtomi Cress., (Fig. 125), P. insularis Sm., P. laboriosus Cress., (col. 
plate 3), Apis mellifera Linn. (various strains and hybrids. ) 
Viereck’s collecting in 1913 did not add to our list of known Min- 
nesota species of bumble bees. He found the above forms well dis- 
tributed over the state on aster and sunflower in August and September. 
