forests of extra-tropical countries, is probably dependent on the
extreme equability and permanence of the climate. Atmospheric
conditions are much more important to the growth of plants than any
others. Their severest struggle for existence is against climate.
As we approach towards regions of polar cold or desert aridity the
variety of groups and species regularly diminishes; more and more
are unable to sustain the extreme climatal conditions, till at
last we find only a few specially organized forms which are able
to maintain their existence. In the extreme north, pine or birch
trees; in the desert, a few palms and prickly shrubs or aromatic
herbs alone survive. In the equable equatorial zone there is no
such struggle against climate. Every form of vegetation has become
alike adapted to its genial heat and ample moisture, which has
probably changed little even throughout geological periods; and the
never-ceasing struggle for existence between the various species
in the same area has resulted in a nice balance of organic forces,
which gives the advantage, now to one, now to another, species, and
prevents any one type of vegetation from monopolising territory to
the exclusion of the rest. The same general causes have led to the
filling up of every place in nature with some specially adapted
form. Thus we find a forest of smaller trees adapted to grow in the
shade of greater trees. Thus we find every tree supporting numerous
other forms of vegetation, and some so crowded with epiphytes of
various kinds that their forks and horizontal branches are veritable
gardens. Creeping ferns and arums run up the smoothest trunks; an
immense variety of climbers hang in tangled masses from the branches
and mount over the highest tree-tops. Orchids, bromelias, arums,
and ferns grow from every boss and crevice, and cover the fallen
and decaying trunks with a graceful drapery. Even these parasites
have their own parasitical growth, their leaves often supporting an
abundance of minute creeping mosses and hepaticæ. But the uniformity
of climate which has led to this rich luxuriance and endless variety
of vegetation is also the cause of a monotony that in time becomes
oppressive. To quote the words of Mr. Belt: “Unknown are the autumn
tints, the bright browns and yellows of English woods; much less the
crimsons, purples, and yellows of Canada, where the dying foliage
rivals, nay, excels, the expiring dolphin in splendour. Unknown the
cold sleep of winter; unknown the lovely awakening of vegetation at
the first gentle touch of spring. A ceaseless round of ever-active
life weaves the fairest scenery of the tropics into one monotonous
whole, of which the component parts exhibit in detail untold variety
and beauty.”[7]
[7] _The Naturalist in Nicaragua_, p. 58.
To the student of nature the vegetation of the tropics will ever
be of surpassing interest, whether for the variety of forms and
structures which it presents, for the boundless energy with which
the life of plants is therein manifested, or for the help which
it gives us in our search after the laws which have determined
the production of such infinitely varied organisms. When, for the
first time, the traveller wanders in these primeval forests, he
can scarcely fail to experience sensations of awe, akin to those
excited by the trackless ocean or the alpine snowfields. There is
a vastness, a solemnity, a gloom, a sense of solitude and of human
insignificance which for a time overwhelm him; and it is only when
the novelty of these feelings have passed away that he is able to
turn his attention to the separate constituents that combine to
produce these emotions, and examine the varied and beautiful forms
of life which, in inexhaustible profusion, are spread around him.
III.
ANIMAL LIFE IN THE TROPICAL FORESTS.
Difficulties of the Subject--General Aspect of the Animal life of
Equatorial Forests--Diurnal Lepidoptera or Butterflies--Peculiar
Habits of Tropical Butterflies--Ants, Wasps, and
Bees--Ants--Special Relations between Ants and Vegetation--Wasps
and Bees--Orthoptera and other Insects--Beetles--Wingless
Insects--General Observations on Tropical
Insects--Birds--Parrots--Pigeons--Picariæ--Cuckoos--Trogons,
Barbets, Toucans and Hornbills--Passeres--Reptiles
and Amphibia--Lizards--Snakes--Frogs and
Toads--Mammalia--Monkeys--Bats--Summary of the Aspects of Animal
life in the Tropics.
The attempt to give some account of the general aspects of animal
life in the equatorial zone, presents far greater difficulties
than in the case of plants. On the one hand, animals rarely play
any important part in scenery, and their entire absence may pass
quite unnoticed; while the abundance, variety, and character of the
vegetation are among those essential features that attract every eye.
On the other hand, so many of the more important and characteristic
types of animal life are restricted to one only out of the three
great divisions of equatorial land, that they can hardly be claimed
as characteristically tropical; while the more extensive zoological
groups which have a wide range in the tropics and do not equally
abound in the temperate zones, are few in number, and often include
such a diversity of forms, structures, and habits, as to render any
typical characterisation of them impossible. We must then, in the
first place, suppose that our traveller is on the look out for all
signs of animal life; and that, possessing a general acquaintance
as an out-door observer with the animals of our own country, he
carefully notes those points in which the forests of the equatorial
zone offer different phenomena. Here, as in the case of plants, we
exclude all zoological science, classifications, and nomenclature,
except in as far as it is necessary for a clear understanding of the
several groups of animals referred to. We shall therefore follow no
systematic order in our notes, except that which would naturally
arise from the abundance or prominence of the objects themselves.
We further suppose our traveller to have no prepossessions, and to
have no favourite group, in the search after which he passes by
other objects which, in view of their frequent occurrence in the
landscape, are really more important.
_General Aspect of the Animal Life of Equatorial Forests._--Perhaps
the most general impression produced by a first acquaintance with
the equatorial forests, is the comparative absence of animal life.
Beast, bird, and insect alike require looking for, and it very often
happens that we look for them in vain. On this subject Mr. Bates,
describing one of his early excursions into the primeval forests of
the Amazon Valley, remarks as follows:--“We were disappointed in not
meeting with any of the larger animals of the forest. There was no
tumultuous movement or sound of life. We did not see or hear monkeys,
and no tapir or jaguar crossed our path. Birds also appeared to be
exceedingly scarce.” Again--“I afterwards saw reason to modify my
opinion, founded on first impressions, with regard to the amount
and variety of animal life in this and other parts of the Amazonian
forests. There is in fact a great variety of mammals, birds, and
reptiles, but they are widely scattered and all excessively shy of
man. The region is so extensive, and uniform in the forest clothing
of its surface, that it is only at long intervals that animals are
seen in abundance, where some particular spot is found which is
more attractive than others. Brazil, moreover, is throughout poor
in terrestrial mammals, and the species are of small size; they
do not, therefore, form a conspicuous feature in the forests. The
huntsman would be disappointed who expected to find here flocks
of animals similar to the buffalo-herds of North America, or the
swarms of antelopes and herds of ponderous pachyderms of Southern
Africa. We often read in books of travel of the silence and gloom
of the Brazilian forests. They are realities, and the impression
deepens on a longer acquaintance. The few sounds of birds are of
that pensive and mysterious character which intensifies the feeling
of solitude rather than imparts a sense of life and cheerfulness.
Sometimes in the midst of the stillness, a sudden yell or scream
will startle one; this comes from some defenceless fruit-eating
animal which is pounced upon by a tiger-cat or a boa-constrictor.
Morning and evening the howling monkeys make a most fearful and
harrowing noise, under which it is difficult to keep up one’s
buoyancy of spirit. The feeling of inhospitable wildness which the
forest is calculated to inspire, is increased tenfold under this
fearful uproar. Often, even in the still midday hours, a sudden
crash will be heard resounding afar through the wilderness, as
some great bough or entire tree falls to the ground.” With a few
verbal alterations these remarks will apply equally to the primeval
forests of the Malay Archipelago; and it is probable that those of
West Africa offer no important differences in this respect. There
is, nevertheless, one form of life which is very rarely absent in
the more luxuriant parts of the tropics, and which is more often so
abundant as to form a decided feature in the scene. It is therefore
the group which best characterises the equatorial zone, and should
form the starting-point for our review. This group is that of the
diurnal Lepidoptera or butterflies.
_Diurnal Lepidoptera._--Wherever in the equatorial zone a
considerable extent of the primeval forest remains, the observer can
hardly fail to be struck by the abundance and the conspicuous beauty
of the butterflies. Not only are they abundant in individuals, but
their large size, their elegant forms, their rich and varied colours,
and the number of distinct species almost everywhere to be met with
are equally remarkable. In many localities near the northern or
southern tropics they are perhaps equally abundant, but these spots
are more or less exceptional; whereas within the equatorial zone,
and with the limitations above stated, butterflies form one of the
most constant and most conspicuous displays of animal life. They
abound most in old and tolerably open roads and pathways through
the forest, but they are also very plentiful in old settlements
in which fruit-trees and shrubbery offer suitable haunts. In the
vicinity of such old towns as Malacca and Amboyna in the East,
and of Para and Rio de Janeiro in the West, they are especially
abundant, and comprise some of the handsomest and most remarkable
species in the whole group. Their aspect is altogether different from
that presented by the butterflies of Europe and of most temperate
countries. A considerable proportion of the species are very large,
six to eight inches across the wings being not uncommon among the
Papilionidæ and Morphidæ, while several species are even larger.
This great expanse of wings is accompanied by a slow flight; and,
as they usually keep near the ground and often rest, sometimes with
closed and sometimes with expanded wings, these noble insects really
look larger and are much more conspicuous objects than the majority
of our native birds. The first sight of the great blue Morphos
flapping slowly along in the forest roads near Para--of the large,
white-and-black semi-transparent Ideas floating airily about in the
woods near Malacca--and of the golden-green Ornithopteras sailing
on bird-like wing over the flowering shrubs which adorn the beach
of the Ké and Aru islands, can never be forgotten by any one with a
feeling of admiration for the new and beautiful in nature. Next to
the size, the infinitely varied and dazzling hues of these insects
most attract the observer. Instead of the sober browns, the plain
yellows, and the occasional patches of red or blue or orange that
adorn our European species, we meet with the most intense metallic
blues, the purest satiny greens, the most gorgeous crimsons, not
in small spots but in large masses, relieved by a black border or
background. In others we have contrasted bands of blue and orange,
or of crimson and green, or of silky yellow relieved by velvety
black. In not a few the wings are powdered over with scales and
spangles of metallic green, deepening occasionally into blue or
golden or deep red spots. Others again have spots and markings as
of molten silver or gold, while several have changeable hues, like
shot-silk or richly-coloured opal. The form of the wings, again,
often attracts attention. Tailed hind-wings occur in almost all
the families, but vary much in character. In some the tails are
broadly spoon-shaped, in others long and pointed. Many have double
or triple tails, and some of the smaller species have them immensely
elongated and often elegantly curled. In some groups the wings are
long and narrow, in others strongly falcate; and though many fly
with immense rapidity, a large number flutter lazily along, as if
they had no enemies to fear and therefore no occasion to hurry.
The number of species of butterflies inhabiting any one locality
is very variable, and is, as a rule, far larger in America than in
the Eastern hemisphere; but it everywhere very much surpasses the
numbers in the temperate zone. A few months’ assiduous collecting
in any of the Malay islands will produce from 150 to 250 species
of butterflies, and thirty or forty species may be obtained any
fine day in good localities. In the Amazon valley, however, much
greater results may be achieved. A good day’s collecting will produce
from forty to seventy species, while in one year at Para about
600 species were obtained. More than 700 species of butterflies
actually inhabit the district immediately around the city of Para,
and this, as far as we yet know, is the richest spot on the globe
for diurnal lepidoptera. At Ega, during four years’ collecting;
Mr. Bates obtained 550 species, and these on the whole surpassed
those of Para in variety and beauty. Mr. Bates thus speaks of a
favourite locality on the margin of the lake near Ega:--“The number
and variety of gaily-tinted butterflies, sporting about in this
grove on sunny days, were so great, that the bright moving flakes
of colour gave quite a character to the physiognomy of the place.
It was impossible to walk far without disturbing flocks of them
from the damp sand at the edge of the water, where they congregated
to imbibe the moisture. They were of almost all colours, sizes,
and shapes; I noticed here altogether eighty species, belonging to
twenty-two distinct genera. The most abundant, next to the very
common sulphur-yellow and orange-coloured kinds, were about a dozen
species of Eunica, which are of large size and conspicuous from
their liveries of glossy dark blue and purple. A superbly adorned
creature, the Callithea Markii, having wings of a thick texture,
coloured sapphire-blue and orange, was only an occasional visitor.
On certain days, when the weather was very calm, two small gilded
species (Symmachia Trochilus and Colubris) literally swarmed on
the sands, their glittering wings lying wide open on the flat
surface.”[8]
[8] _The Naturalist on the Amazons_, 2nd edit. p. 331.
When we consider that only sixty-four species of butterflies have
been found in Britain and about 150 in Germany, many of which are
very rare and local, so that these numbers are the result of the
work of hundreds of collectors for a long series of years, we see
at once the immense wealth of the equatorial zone in this form of
life.
_Peculiar Habits of Tropical Butterflies._--The habits of the
butterflies of the tropics offer many curious points rarely or never
observed among those of the temperate zone. The majority, as with
us, are truly diurnal, but there are some Eastern Morphidæ and the
entire American family Brassolidæ, which are crepuscular, coming
out after sunset and flitting about the roads till it is nearly
dark. Others, though flying in the daytime, are only found in the
gloomiest recesses of the forest, where a constant twilight may
be said to prevail. The majority of the species fly at a moderate
height (from five to ten feet above the ground) while a few usually
keep higher up and are difficult to capture; but a large number,
especially the Satyridæ, many Erycinidæ, and some few Nymphalidæ,
keep always close to the ground, and usually settle on or among the
lowest herbage. As regards the mode of flight, the extensive and
almost exclusively tropical families of Heliconidæ and Danaidæ, fly
very slowly, with a gentle undulating or floating motion which is
almost peculiar to them. Many of the strong-bodied Nymphalidæ and
Hesperidæ, on the other hand, have an excessively rapid flight,
darting by so swiftly that the eye cannot follow them, and in some
cases producing a deep sound louder than that of the humming-birds.
The places they frequent, and their mode of resting, are various
and often remarkable. A considerable number frequent damp open
places, especially river sides and the margins of pools, assembling
together in flocks of hundreds of individuals; but these are almost
entirely composed of males, the females remaining in the forests
where, towards the afternoon, their partners join them. The majority
of butterflies settle upon foliage and on flowers, holding their
wings erect and folded together, though early in the morning, or
when newly emerged from the chrysalis, they often expand them to
the sun. Many, however, have special stations and attitudes. Some
settle always on tree-trunks, usually with the wings erect, but
the Ageronias expand them and always rest with the head downwards.
Many Nymphalidæ prefer resting on the top of a stick; others choose
bushes with dead leaves; others settle on rocks or sand or in dry
forest paths. Pieces of decaying animal or vegetable matter are
very attractive to certain species, and if disturbed they will
sometimes return to the same spot day after day. Some Hesperidæ,
as well as species of the genera Cyrestis and Symmachia, and some
others, rest on the ground with their wings fully expanded and
pressed closely to the surface, as if exhibiting themselves to the
greatest advantage. The beautiful little Erycinidæ of South America
vary remarkably in their mode of resting. The majority always rest
on the under surface of leaves with their wings expanded, so that
when they settle they suddenly disappear from sight. Some, however,
as the elegant gold-spotted Helicopis cupido, rest beneath leaves
with closed wings. A few, as the genera Charis and Themone, for
example, sit on the upper side of leaves with their wings expanded;
while the gorgeously-coloured Erycinas rest with wings erect and
exposed as in the majority of butterflies. The Hesperidæ vary in
a somewhat similar manner. All rest on the upper side of leaves
or on the ground, but some close their wings, others expand them,
and a third group keep the upper pair of wings raised while the
hind wings are expanded, a habit found in some of our European
species. Many of the Lycænidæ, especially the Theclas, have the
curious habit, while sitting with their wings erect, of moving the
lower pair over each other in opposite directions, giving them the
strange appearance of excentrically revolving discs.
The great majority of butterflies disappear at night, resting
concealed amid foliage, or on sticks or trunks, or in such places as
harmonise with their colours and markings; but the gaily-coloured
Heliconidæ and Danaidæ seek no such concealment, but rest at night
hanging at the ends of slender twigs or upon fully exposed leaves.
Being uneatable they have no enemies and need no concealment.
Day-flying moths of brilliant or conspicuous colours are also
comparatively abundant in the tropical forests. Most magnificent
of all are the Uranias, whose long-tailed green-and-gold powdered
wings resemble those of true swallow-tailed butterflies. Many
Agaristidæ of the East are hardly inferior in splendour, while hosts
of beautiful clear-wings and Ægeriidæ add greatly to the insect
beauty of the equatorial zone.
The wonderful examples afforded by tropical butterflies of the
phenomena of sexual and local variation, of protective modifications,
and of mimicry, have been fully discussed elsewhere. For the study of
the laws of variation in all its forms, these beautiful creatures are
unsurpassed by any class of animals; both on account of their great
abundance, and the assiduity with which they have been collected and
studied. Perhaps no group exhibits the distinctions of species and
genera with such precision and distinctness, due, as Mr. Bates has
well observed, to the fact that all the superficial signs of change
in the organization are exaggerated, by their affecting the size,
shape, and colour, of the wings, and the distribution of the ribs
or veins which form their framework. The minute scales or feathers
with which the wings are clothed are coloured in regular patterns,
which vary in accordance with the slightest change in the conditions
to which the species are exposed. These scales are sometimes absent
in spots or patches, and sometimes over the greater part of the
wings, which then become transparent, relieved only by the dark veins
and by delicate shades or small spots of vivid colour, producing a
special form of delicate beauty characteristic of many South American
butterflies. The following remark by Mr. Bates will fitly conclude
our sketch of these lovely insects:--“It may be said, therefore,
that on these expanded membranes Nature writes, as on a tablet, the
story of the modifications of species, so truly do all the changes
of the organization register themselves thereon. And as the laws of
Nature must be the same for all beings, the conclusions furnished
by this group of insects must be applicable to the whole organic
world; therefore the study of butterflies--creatures selected as
the types of airiness and frivolity--instead of being despised,
will some day be valued as one of the most important branches of
biological science.”[9]
[9] Bates, _The Naturalist on the Amazons_, 2nd edit. p. 413.
Next after the butterflies in importance, as giving an air of life
and interest to tropical nature, we must place the birds; but to
avoid unnecessary passage, to and fro, among unrelated groups, it
will be best to follow on with a sketch of such other groups of
insects as from their numbers, variety, habits, or other important
features, attract the attention of the traveller from colder
climates. We begin then with a group, which owing to their small
size and obscure colours would attract little attention, but which
nevertheless, by the universality of their presence, their curious
habits, and the annoyance they often cause to man, are sure to force
themselves upon the attention of every one who visits the tropics.
_Ants, Wasps, and Bees._--The hymenopterous insects of the tropics
are, next to the butterflies, those which come most prominently
before the traveller, as they love the sunshine, frequent gardens,
houses, and roadways as well as the forest shades, never seek
concealment, and are many of them remarkable for their size or form,
or are adorned with beautiful colours and conspicuous markings.
Although ants are, perhaps, on the whole the smallest and the least
attractive in appearance of all tropical insects, yet, owing to
their being excessively abundant and almost omnipresent, as well
as on account of their curious habits and the necessity of being
ever on the watch against their destructive powers, they deserve
our first notice.