CHAPTER XI 
HUMBLE-BEES AND OTHER MATTERS. 
Two humble-bees, Bombus thoracicus and B. viola- 
ceus, are found on the pampas; the first, with a 
primrose yellow thorax, and the extremity of the 
abdomen bright rufous, slightly resembles the 
English B. terrestris; the rarer species, which is a 
trifle smaller than the first, is of a uniform intense 
black, the body having the appearance of velvet, the 
wings being of a deep violaceous blue. 
A census of the humble-bees in any garden or 
field always shows that the yellow bees outnumber 
the black in the proportion of about seven to one; 
and I have also found their nests for many years 
in the same proportion; about seven nests of the 
yellow to one nest of the black species. In habits 
they are almost identical, and when two species so 
closely allied are found inhabiting the same locality, 
it is only reasonable to infer that one possesses 
some advantage over the other, and that the least 
favoured species will eventually disappear. In this 
case, where one so greatly outnumbers the other, it 
might be thought that the rarer species is dying 
out, or that, on the contrary, it is a new-comer 
destined to supplant the older more numerous 
species. Yet, during the twenty years I have ob- 
