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 first made; later in the
season the old cocoons are utilized for storing honey. The wax is
chocolate-coloured, and almost the only difference I can find in the
economy of the two species is that the black bee uses a large quantity
of wax in plastering the interior of its nest. The egg-cell of the
yellow bee always contains from twelve to sixteen eggs; that of the
black bee from ten to fourteen; and the eggs of this species are the
largest though the bee is smallest. At the entrance on the edge of the
mound one bee is usually stationed, and, when approached, it hums a
shrill challenge, and throws itself into a menacing attitude. The sting
is exceedingly painful.
One summer I was so fortunate as to discover two nests of the two kinds
within twelve yards of each other, and I resolved to watch them very
carefully, in order to see whether the two species ever came into
collision, as sometimes happens with ants of different species living
close together. Several times I saw a yellow bee leave its own nest and
hover round or settle on the neighbouring one, upon which the sentinel
black bee would attack and drive it off. One day, while watching, I was
delighted to see a yellow bee actually enter its neighbour's nest, the
sentinel being off duty. In about five minutes' time it came out again
and flew away unmolested. I concluded from this that humble-bees, like
their relations of the hive, occasionally plunder each other's sweets.
On another occasion I found a black bee dead at the entrance of the
yellow bees' nest; doubtless this individual had been caught in the act
of stealing honey, and, after it had been stung to death, it had been
dragged out and left there as a warning to others with like felonious
intentions.
There is one striking difference between the two species. The yellow bee
is inodorous; the black bee, when angry and attacking, emits an
exceedingly powerful odour: curiously enough, this smell is identical in
character with that made when angry by all the wasps of the South
American genus Pepris--dark blue wasps with red wings. This odour at
first produces a stinging sensation on the nerve of smell, but when
inhaled in large measure becomes very nauseating. On one occasion, while
I was opening a nest, several of the bees buzzing round my head and
thrusting their stings through the veil I wore for protection, gave out
so pungent a smell that I found it unendurable, and was compelled to
retreat.
It seems strange that a species armed with a venomous sting and
possessing the fierce courage of the humble-bee should also have this
repulsive odour for a protection. It is, in fact, as incongruous as it
would be were our soldiers provided with guns and swords first, and
after with phials of assafoatida to be uncorked in the face of an enemy.
Why, or how, animals came to be possessed of the power of emitting
pestiferous odours is a mystery; we only see that natural selection has,
in some mstances, chiefly among insects, taken advantage of it to
furnish some of the weaker, more unprotected species with a means of
escape from their enemies. The most stinking example I know is that of a
large hairy caterpillar I have found on dry wood in Patagonia, and
which, when touched, emits an intensely nauseous effluvium. Happily it
is very volatile, but while it lasts it is even more detestable than
that of the skunk.
The skunk itself offers perhaps the one instance amongst the higher
vertebrates of an animal in which all the original instincts of
self-preservation have died out, giving place to this lower kind of
protection. All the other members of the family it belongs to are
cunning, swift of foot, and, when overtaken, fierce-tempered and well
able to defend themselves with their powerful well-armed jaws.
For some occult reason they are provided with a gland charged with a
malodorous secretion; and out of this mysterious liquor Nature has
elaborated the skunk's inglorious weapon. The skunk alone when attacked
makes no attempt to escape or to defend itself by biting; but, thrown by
its agitation into a violent convulsion, involuntarily discharges its
foetid liquor into the face of an opponent. When this animal had once
ceased to use so good a weapon as its teeth in defending itself,
degenerating at the same time into a slow-moving creature, without fear
and without cunning, the strength and vileness of its odour would be
continually increased by the cumulative process of natural selection:
and how effective the protection has become is shown by the abundance of
the species throughout the whole American continent. It is lucky for
mankind--especially for naturalists and sportsmen--that other species
have not been improved in the same direction.
But what can we say of the common deer of the pampas (Cervus
campestris), the male of which gives out an effluvium quite as
far-reaching although not so abominable in character as that of the
Mephitis? It comes in disagreeable whiffs to the human nostril when the
perfumer of the wilderness is not even in sight. Yet it is not a
protection; on the contrary, it is the reverse, and, like the dazzling
white plumage so attractive to birds of prey, a direct disadvantage,
informing all enemies for leagues around of its whereabouts. It is not,
therefore, strange that wherever pumas are found, deer are never very
abundant; the only wonder is that, like the ancient horse of America,
they have not become extinct.
The gauchos of the pampas, however, give _a reason_ for the powerful
smell of the male deer; and, after some hesitation, I have determined to
set it down here, for the reader to accept or reject, as he thinks
proper. I neither believe nor disbelieve it; for although I do not put
great faith in gaucho natural history, my own observations have not
infrequently confirmed statements of theirs, which a sceptical person
would have regarded as wild indeed. To give one instance: I heard a
gaucho relate that while out riding he had been pursued for a
considerable distance by a large spider; his hearers laughed at him for
a romancer; but as I myself had been attacked and pursued, both when on
foot and on horseback, by a large wolf-spider, common on the pampas, I
did not join in the laugh. They say that the effluvium of C. campestris
is abhorrent to snakes of all kinds, just as pyrethrum powder is to most
insects, and even go so far as to describe its effect as fatal to them;
according to this, the smell is therefore a protection to the deer. In
places where venomous snakes are extremely abundant, as in the Sierra
district on the southern pampas of Buenos Ayres, the gaucho frequently
ties a strip of the male deer's skin, which retains its powerful odour
for an indefinite time, round the neck of a valuable horse as a
protection. It is certain that domestic animals are frequently lost here
through snake-bites. The most common poisonous species--the
Craspedo-cephalus alternatus, called _Vivora de la Cruz_ in the
vernacular--has neither bright colour nor warning rattle to keep off
heavy hoofs, and is moreover of so sluggish a temperament that it will
allow itself to be trodden on before stirring, with the result that its
fangs are not infrequently struck into the nose or foot of browsing
beast. Considering, then, the conditions in which C. campestris is
placed--and it might also be supposed that venomous snakes have in past
times been much more numerous than they are now--it is not impossible to
believe that the powerful smell it emits has been made protective,
especially when we see in other species how repulsive odours have been
turned to account by the principle of natural selection.
After all, perhaps the wild naturalist of the pampas knows what he is
about when he ties a strip of deer-skin to the neck of his steed and
turns him loose to graze among the snakes.
The gaucho also affirms that the deer cherishes a wonderful animosity
against snakes; that it becomes greatly excited when it sees one, and
proceeds at once to destroy it; _they say,_ by running round and round
it in a circle, emitting its violent smell in larger measure, until the
snake dies of suffocation. It is hard to believe that the effect can be
so great; but that the deer is a snake hater and killer is certainly
true: in North America, Ceylon, and other districts deer have been
observed excitedly leaping on serpents, and killing them with their
sharp cutting hoofs.