IT 
Si ty ies) Vite ww SURPER-B RE. 
THE most interesting and, in my experience, the 
deadliest enemies to which several of the commonest 
species of humble-bees are liable to fall a prey are 
bees so closely resembling the true humble-bees 
themselves that only a student can tell the differ- 
ence between them. These bees were first recog- 
nised to be distinct from the ordinary humble-bees 
in 1802 by Kirby, who noticed among other differ- 
ences that the females lacked the pollen-collecting 
apparatus on the hind legs,’ and thirty years later 
Lepeletier gave them the name of Pszthyrus. 
Each species of Pszthyrus breeds only in the 
nests of its own particular species of Bomdéus. The 
Psithyri produce no workers, and some of the early 
observers who saw them in the nests of the Aomzéz, 
noticing that they appeared to live in perfect 
harmony with their hosts, suggested that they 
might render them some important service. But 
it was soon discovered that their association with 
the Gomdz was to the disadvantage of the latter, and 
they came to be regarded as commensals living 
1 Monographia Apum Anglia, vol. i. pp. 209, 210. 
59 
