underground, others in the thatched roof on the under-surface of
which they make their nests, while covered ways of earth are often
constructed upon the posts and doors. In the forests they live on
the ground, under leaves, on the branches of trees, or under rotten
bark; while others actually dwell in living plants, which seem to be
specially modified so as to accommodate them. Some sting severely,
others only bite; some are quite harmless, others exceedingly
destructive. The number of different kinds is very great. In India
and the Malay Archipelago nearly 500 different species have been
found, and other tropical countries are no doubt equally rich. I
will first give some account of the various species observed in the
Malay Islands, and afterwards describe some of the more interesting
South American groups, which have been so carefully observed by
Mr. Bates on the Amazon and by Mr. Belt in Nicaragua.
Among the very commonest ants in all parts of the world are the
species of the family Formicidæ, which do not sting, and are most
of them quite harmless. Some make delicate papery nests, others
live under stones or among grass. Several of them accompany Aphides
to feed upon the sweet secretions from their bodies. They vary
in size from the large _Formica gigas_, more than an inch long,
to minute species so small as to be hardly visible. Those of the
genus Polyrachis, which are plentiful in all Eastern forests, are
remarkable for the extraordinary hooks and spines with which their
bodies are armed, and they are also in many cases beautifully
sculptured or furrowed. They are not numerous individually, and are
almost all arboreal, crawling about bark and foliage. One species
has processes on its back just like fish-hooks, others are armed
with long, straight spines. They generally form papery nests on
leaves, and when disturbed they rush out and strike their bodies
against the nest so as to produce a loud rattling noise; but the nest
of every species differs from those of all others either in size,
shape, or position. As they all live in rather small communities
in exposed situations, are not very active, and are rather large
and conspicuous, they must be very much exposed to the attacks of
insectivorous birds and other creatures; and, having no sting or
powerful jaws with which to defend themselves, they would be liable
to extermination without some special protection. This protection
they no doubt obtain by their hard smooth bodies, and by the curious
hooks, spines, points and bristles with which they are armed, which
must render them unpalatable morsels, very liable to stick in the
jaws or throats of their captors.
A curious and very common species in the Malay Islands is the green
ant (_Œcophylla smaragdina_), a rather large, long-legged, active,
and intelligent-looking creature, which lives in large nests formed
by glueing together the edges of leaves, especially of Zingiberaceous
plants. When the nest is touched a number of the ants rush out,
apparently in a great rage, stand erect, and make a loud rattling
noise by tapping against the leaves. This no doubt frightens away
many enemies, and is their only protection; for though they attempt
to bite, their jaws are blunt and feeble, and they do not cause
any pain.
Coming now to the stinging groups, we have first a number of solitary
ants of the great genus Odontomachus, which are seen wandering
about the forest, and are conspicuous by their enormously long and
slender hooked jaws. These are not powerful, but serve admirably
to hold on by while they sting, which they do pretty severely. The
Poneridæ are another group of large-sized ants which sting acutely.
They are very varied in species but are not abundant individually.
The _Ponera clavata_ of Guiana, is one of the worst stinging ants
known. It is a large species frequenting the forests on the ground,
and is much dreaded by the natives, as its sting produces intense
pain and illness. I was myself stung by this or an allied species
when walking barefoot in the forest on the Upper Rio Negro. It
caused such pain and swelling of the leg that I had some difficulty
in reaching home, and was confined to my room for two days. Sir
Robert Schomburgh suffered more; for he fainted with the pain, and
had an attack of fever in consequence.
We now come to the Myrmecidæ, which may be called the destroying
ants from their immense abundance and destructive propensities.
Many of them sting most acutely, causing a pain like that of a
sudden burn, whence they are often called “fire-ants.” They often
swarm in houses and devour everything eatable. Isolation by water
is the only security, and even this does not always succeed, as a
little dust on the surface will enable the smaller species to get
across. Oil is, however, an effectual protection, and after many
losses of valuable insect specimens, for which ants have a special
affection, I always used it. One species of this group, a small
black Crematogaster, took possession of my house in New Guinea,
building nests in the roof and making covered ways down the posts
and across the floor. They also occupied the setting boards I used
for pinning out my butterflies, filling up the grooves with cells
and storing them with small spiders. They were in constant motion,
running over my table, in my bed, and all over my body. Luckily,
they were diurnal, so that on sweeping out my bed at night I could
get on pretty well; but during the day I could always feel some
of them running over my body, and every now and then one would
give me a sting so sharp as to make me jump and search instantly
for the offender, who was usually found holding on tight with his
jaws, and thrusting in his sting with all his might. Another genus,
Pheidole, consists of forest ants, living under rotten bark or in
the ground, and very voracious. They are brown or blackish, and are
remarkable for their great variety of size and form in the same
species, the largest having enormous heads many times larger than
their bodies, and being at least a hundred times as bulky as the
smallest individuals. These great-headed ants are very sluggish
and incapable of keeping up with the more active small workers,
which often surround and drag them along as if they were wounded
soldiers. It is difficult to see what use they can be in the colony,
unless, as Mr. Bates suggests, they are mere baits to be attacked
by insect-eating birds, and thus save their more useful companions.
These ants devour grubs, white ants, and other soft and helpless
insects, and seem to take the place of the foraging ants of America
and driver-ants of Africa, though they are far less numerous and
less destructive. An allied genus, Solenopsis, consists of red ants,
which, in the Moluccas, frequent houses, and are a most terrible
pest. They form colonies underground, and work their way up through
the floors, devouring everything eatable. Their sting is excessively
painful, and some of the species are hence called fire-ants. When
a house is infested by them, all the tables and boxes must be
supported on blocks of wood or stone placed in dishes of water, as
even clothes not newly washed are attractive to them; and woe to the
poor fellow who puts on garments in the folds of which a dozen of
these ants are lodged. It is very difficult to preserve bird skins
or other specimens of natural history where these ants abound, as
they gnaw away the skin round the eyes and the base of the bill; and
if a specimen is laid down for even half an hour in an unprotected
place it will be ruined. I remember once entering a native house to
rest and eat my lunch; and having a large tin collecting box full
of rare butterflies and other insects, I laid it down on the bench
by my side. On leaving the house I noticed some ants on it, and on
opening the box found only a mass of detached wings and bodies,
the latter in process of being devoured by hundreds of fire-ants.
The celebrated Saüba ant of America (_Œcodoma cephalotes_) is
allied to the preceding, but is even more destructive, though it
seems to confine itself to vegetable products. It forms extensive
underground galleries, and the earth brought up is deposited on
the surface, forming huge mounds sometimes thirty or forty yards
in circumference, and from one to three feet high. On first seeing
these vast deposits of red or yellow earth in the woods near Para,
it was hardly possible to believe they were not the work of man,
or at least of some burrowing animal. In these underground caves
the ants store up large quantities of leaves, which they obtain
from living trees. They gnaw out circular pieces and carry them
away along regular paths a few inches wide, forming a stream of
apparently animated leaves. The great extent of the subterranean
workings of these ants is no doubt due in part to their permanence
in one spot, so that when portions of the galleries fall in or are
otherwise rendered useless, they are extended in another direction.
When in the island of Marajo, near Para, I noticed a path along
which a stream of Saübas were carrying leaves from a neighbouring
thicket; and a relation of the proprietor assured me that he had
known that identical path to be in constant use by the ants for
twenty years. Thus we can account for the fact mentioned by Mr.
Bates, that the underground galleries were traced by smoke for a
distance of seventy yards in the Botanic Gardens at Para; and for
the still more extraordinary fact related by the Rev. Hamlet Clark,
that an allied species in Rio de Janeiro has excavated a tunnel
under the bed of the river Parahyba, where it is about a quarter
of a mile wide! These ants seem to prefer introduced to native
trees; and young plantations of orange, coffee, or mango trees are
sometimes destroyed by them, so that where they abound cultivation
of any kind becomes almost impossible. Mr. Belt ingeniously accounts
for this preference, by supposing that for ages there has been a
kind of struggle going on between the trees and the ants; those
varieties of trees which were in any way distasteful or unsuitable
escaping destruction, while the ants were becoming slowly adapted
to attack new trees. Thus in time the great majority of native
trees have acquired some protection against the ants, while foreign
trees, not having been so modified, are more likely to be suitable
for their purposes. Mr. Belt carried on war against them for four
years to protect his garden in Nicaragua, and found that carbolic
acid and corrosive sublimate were most effectual in destroying or
driving them away.
The use to which the ants put the immense quantities of leaves
they carry away has been a great puzzle, and is, perhaps, not yet
quite understood. Mr. Bates found that the Amazon species used
them to thatch the domes of earth covering the entrances to their
subterranean galleries, the pieces of leaf being carefully covered
and kept in position by a thin layer of grains of earth. In Nicaragua
Mr. Belt found the underground cells full of a brown flocculent
matter, which he considers to be the gnawed leaves connected by a
delicate fungus which ramifies through the mass and which serves
as food for the larvæ; and he believes that the leaves are really
gathered as manure-heaps to favour the growth of this fungus!
When they enter houses, which they often do at night, the Saübas
are very destructive. Once, when travelling on the Rio Negro, I had
bought about a peck of rice, which was tied up in a large cotton
handkerchief and placed on a bench in a native house where we were
spending the night. The next morning we found about half the rice
on the floor, the remainder having been carried away by the ants;
and the empty handkerchief was still on the bench, but with hundreds
of neat cuts in it reducing it to a kind of sieve.[10]
[10] For a full and most interesting description of the habits and
instincts of this ant, see Bates’ _Naturalist on the Amazons_, 2nd
edit. pp. 11-18; and Belt’s _Naturalist in Nicaragua_, pp. 71-84.
The foraging ants of the genus Eciton are another remarkable group,
especially abundant in the equatorial forests of America. They
are true hunters, and seem to be continually roaming about the
forests in great bands in search of insect prey. They especially
devour maggots, caterpillars, white ants, cockroaches, and other
soft insects; and their bands are always accompanied by flocks
of insectivorous birds who prey upon the winged insects that are
continually trying to escape from the ants. They even attack wasps’
nests, which they cut to pieces and then drag out the larvæ. They
bite and sting severely, and the traveller who accidentally steps
into a horde of them will soon be overrun, and must make his escape
as quickly as possible. They do not confine themselves to the ground,
but swarm up bushes and low trees, hunting every branch, and clearing
them of all insect life. Sometimes a band will enter a house, like
the driver ants in Africa, and clear it of cockroaches, spiders,
centipedes, and other insects. They seem to have no permanent abode
and to be ever wandering about in search of prey, but they make
temporary habitations in hollow trees or other suitable places.
Perhaps the most extraordinary of all ants are the blind species
of Eciton discovered by Mr. Bates, which construct a covered way
or tunnel as they march along. On coming near a rotten log, or any
other favourable hunting ground, they pour into all its crevices in
search of booty, their covered way serving as a protection to retire
to in case of danger. These creatures, of which two species are
known, are absolutely without eyes; and it seems almost impossible to
imagine that the loss of so important a sense-organ can be otherwise
than injurious to them. Yet on the theory of natural selection the
successive variations by which the eyes were reduced and ultimately
lost must all have been useful. It is true they do manage to exist
without eyes; but that is probably because, as sight became more
and more imperfect, new instincts or new protective modifications
were developed to supply its place, and this does not in any way
account for so wide-spread and invaluable a sense having become
permanently lost, in creatures which still roam about and hunt for
prey very much as do their fellows who can see.
_Special Relations between Ants and Vegetation._--Attention has
recently been called to the very remarkable relations existing
between some trees and shrubs and the ants which dwell upon them.
In the Malay Islands are several curious shrubs belonging to the
Cinchonaceæ, which grow parasitically on other trees, and whose
swollen stems are veritable ants’ nests. When very young the stems
are like small, irregular prickly tubers, in the hollows of which
ants establish themselves; and these in time grow into irregular
masses the size of large gourds, completely honeycombed with the
cells of ants. In America there are some analogous cases occurring
in several families of plants, one of the most remarkable being
that of certain Melastomas which have a kind of pouch formed by an
enlargement of the petiole of the leaf, and which is inhabited by
a colony of small ants. The hollow stems of the Cecropias (curious
trees with pale bark and large palmate leaves which are white
beneath) are always tenanted by ants, which make small entrance holes
through the bark; but here there seems no special adaptation to the
wants of the insect. In a species of Acacia observed by Mr. Belt,
the thorns are immensely large and hollow, and are always tenanted
by ants. When young these thorns are soft and full of a sweetish
pulpy substance, so that when the ants first take possession they
find a store of food in their house. Afterwards they find a special
provision of honey-glands on the leaf-stalks, and also small yellow
fruit-like bodies which are eaten by the ants; and this supply of
food permanently attaches them to the plant. Mr. Belt believes, after
much careful observation, that these ants protect the plant they
live on from leaf-eating insects, especially from the destructive
Saüba ants,--that they are in fact a standing army kept for the
protection of the plant! This view is supported by the fact that
other plants--Passion-flowers, for example--have honey-secreting
glands on the young leaves and on the sepals of the flower-buds
which constantly attract a small black ant. If this view is correct,
we see that the need of escaping from the destructive attacks of
the leaf-cutting ants has led to strange modifications in many
plants. Those in which the foliage was especially attractive to
these enemies were soon weeded out unless variations occurred which
tended to preserve them. Hence the curious phenomenon of insects
specially attracted to certain plants to protect them from other
insects; and the existence of the destructive leaf-cutting ant in
America will thus explain why these specially modified plants are
so much more abundant there than in the Old World, where no ants
with equally destructive habits appear to exist.
_Wasps and Bees._--These insects are excessively numerous in the
tropics, and, from their large size, their brilliant colours,
and their great activity, they are sure to attract attention.
Handsomest of all, perhaps, are the Scoliadæ, whose large and
rather broad hairy bodies, often two inches long, are richly banded
with yellow or orange. The Pompilidæ comprise an immense number of
large and handsome insects, with rich blue-black bodies and wings
and exceedingly long legs. They may often be seen in the forests
dragging along large spiders, beetles, or other insects they have
captured. Some of the smaller species enter houses and build earthen
cells which they store with small green spiders rendered torpid by
stinging, to feed the larvæ. The Eumenidæ are beautiful wasps with
very long pedunculated bodies, which build papery cones covering
a few cells in which the eggs are deposited. Among the bees the
Xylocopas, or wood-boring bees, are remarkable. They resemble large
humble-bees, but have broad, flat, shining bodies, either black
or banded with blue; and they often bore large cylindrical holes
in the posts of houses. True honey-bees are chiefly remarkable in
the East for their large semi-circular combs suspended from the
branches of the loftiest trees without any covering. From these
exposed nests large quantities of wax and honey are obtained, while
the larvæ afford a rich feast to the natives of Borneo, Timor, and
other islands where bees abound. They are very pugnacious, and, when
disturbed will follow the intruders for miles, stinging severely.
_Orthoptera and other Insects._--Next to the butterflies and ants,
the insects that are most likely to attract the attention of the
stranger in the tropics are the various forms of Mantidæ and
Phasmidæ, some of which are remarkable for their strange attitudes
and bright colours; while others are among the most singular of
known insects, owing to their resemblance to sticks and leaves.
The Mantidæ--usually called “praying insects,” from their habit
of sitting with their long fore-feet held up as if in prayer--are
really tigers among insects, lying in wait for their prey, which
they seize with their powerful serrated fore-feet. They are usually
so coloured as to resemble the foliage among which they live, and
as they sit quite motionless, they are not easily perceived.
The Phasmidæ are perfectly inoffensive leaf-eating insects of very
varied forms; some being broad and leaf-like, while others are long
and cylindrical so as to resemble sticks, whence they are often
called walking-stick insects. The imitative resemblance of some
of these insects to the plants on which they live is marvellous.
The true leaf-insects of the East, forming the genus Phyllium, are
the size of a moderate leaf, which their large wing-covers and the
dilated margins of the head, thorax and legs cause them exactly to
resemble. The veining of the wings, and their green tint, exactly
corresponds to that of the leaves of their food-plant; and as they
rest motionless during the day, only feeding at night, they the more
easily escape detection. In Java they are often kept alive on a
branch of the guava tree; and it is a common thing for a stranger,
when asked to look at this curious insect, to inquire where it is,
and on being told that it is close under his eyes, to maintain that
there is no insect at all, but only a branch with green leaves.
The larger wingless stick-insects are often eight inches to a foot
long. They are abundant in the Moluccas; hanging on the shrubs
that line the forest-paths; and they resemble sticks so exactly,
in colour, in the small rugosities of the bark, in the knots and
small branches, imitated by the joints of the legs, which are
either pressed close to the body, or stuck out at random, that it
is absolutely impossible, by the eye alone, to distinguish the real
dead twigs which fall down from the trees overhead from the living
insects. The writer has often looked at them in doubt, and has been
obliged to use the sense of touch to determine the point. Some are
small and slender like the most delicate twigs; others again have
wings; and it is curious that these wings are often beautifully
coloured, generally bright pink, sometimes yellow, and sometimes
finely banded with black; but when at rest these wings fold up so
as to be completely concealed under the narrow wing-covers, and the
whole insect is then green or brown, and almost invisible among the
twigs or foliage. To increase the resemblance to vegetation, some of
these Phasmas have small green processes in various parts of their
bodies looking exactly like moss. These inhabit damp forests both
in the Malay islands and in America, and they are so marvellously
like moss-grown twigs that the closest examination is needed to
satisfy oneself that it is really a living insect we are looking
at.
Many of the locusts are equally well-disguised, some resembling green
leaves, others those that are brown and dead; and the latter often
have small transparent spots on the wings, looking like holes eaten
through them. That these disguises deceive their natural enemies
is certain, for otherwise the Phasmidæ would soon be exterminated.
They are large and sluggish, and very soft and succulent; they have
no means of defence or of flight, and they are eagerly devoured
by numbers of birds, especially by the numerous cuckoo tribe,
whose stomachs are often full of them; yet numbers of them escape
destruction, and this can only be due to their vegetable disguises.
Mr. Belt records a curious instance of the actual operation of this
kind of defence in a leaf-like locust, which remained perfectly
quiescent in the midst of a host of insectivorous ants, which ran
over it without finding out that it was an insect and not a leaf! It
might have flown away from them, but it would then instantly have
fallen a prey to the numerous birds which always accompany these
roaming hordes of ants to feed upon the insects that endeavour to
escape. Far more conspicuous than any of these imitative species
are the large locusts, with rich crimson or blue-and-black spotted
wings. Some of these are nearly a foot in expanse of wings; they fly
by day, and their strong spiny legs probably serve as a protection
against all the smaller birds. They cannot be said to be common;
but when met with they fully satisfy our notions as to the large
size and gorgeous colours of tropical insects.
_Beetles._--Considering the enormous numbers and endless variety
of the beetle tribe that are known to inhabit the tropics, they
form by no means so prominent a feature in the animal life of the
equatorial zone as we might expect. Almost every entomologist is
at first disappointed with them. He finds that they have to be
searched for almost as much as at home, while those of large size
(except one or two very common species) are rarely met with. The
groups which most attract attention from their size and beauty, are
the Buprestidæ and the Longicorns. The former are usually smooth
insects of an elongate ovate form, with very short legs and antennæ,
and adorned with the most glowing metallic tints. They abound on
fallen tree-trunks and on foliage, in the hottest sunshine, and are
among the most brilliant ornaments of the tropical forests. Some
parts of the temperate zone, especially Australia and Chili, abound
in Buprestidæ which are equally beautiful; but the largest species
are only found within the tropics, those of the Malay islands being
the largest of all.