Ch. 11: Humble Bees and other Matters

Two humble-bees, Bombus thoracicus and B. violaceus, 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 observed them, there has occurred no change in their relative
positions; though both have greatly increased in numbers during that
time, owing to the spread of cultivation. And yet it would scarcely be
too much to expect some marked change in a period so long as that, even
through the slow-working agency of natural selection; for it is not as
if there had been an exact balance of power between them. In the same
period of time I have seen several species, once common, almost or quite
disappear, while others, very low down as to numbers, have been exalted
to the first rank. In insect life especially, these changes have been
numerous, rapid, and widespread.

In the district where, as a boy, I chased and caught tinamous, and also
chased ostriches, but failed to catch them, the continued presence of
our two humble-bees, sucking the same flowers and making their nests in
the same situations, has remained a puzzle to my mind.

The site of the nest is usually a slight depression in the soil in the
shelter of a cardoon bush. The bees deepen the hollow by burrowing in
the earth; and when the spring foliage sheltering it withers up, they
construct a dome-shaped covering of small sticks, thorns, and leaves
bitten into extremely minute pieces. They sometimes take possession of a
small hole or cavity in the ground, and save themselves the labour of
excavation.

Their architecture closely resembles that of B. terrestris. They make
rudely-shaped oval honey-cells, varying from half an inch to an inch and
a half in length, the smaller ones being the