Commence journey up San Juan river.
Palms and wild canes.
Plantations.
The Colorado river.
Proposed improvement of the river.
Progress of the delta.
Mosquitoes.
Disagreeable night.
Fine morning.
Vegetation of the banks.
Seripiqui river.
Mot-mots.
Foraging ants: their method of hunting.
Ant-thrushes.
They attack the nests of other ants.
Birds' nests, how preserved from them.
Reasoning powers in ants.
Parallel between the Mammalia and the Hymenoptera.
Utopia.
I FOUND at Greytown the mail-boat of the Chontales Gold-Mining
Company, which came down monthly in charge of Captain Anderson, an
Englishman who had knocked about all over the world. The crew
consisted of four Mosquito negroes, who are celebrated on this
coast for their skill as boatmen. Besides the crew, we were taking
three other negroes up to the mines, and with my boxes we were
rather uncomfortably crowded for a long journey. The canoe itself
was made from the trunk of a cedar-tree (Cedrela odorata). It had
been hollowed out of a single log, and the sides afterwards built
up higher with planking. This makes a very strong boat, the
strength and thickness being where it is most required, at the
bottom, to withstand the thumping about amongst the rocks of the
rapids. I was once in one, coming down a dangerous rapid on the
river Gurupy, in Northern Brazil, when we were driven with the full
force of the boiling stream broadside upon a rock, with such force
that we were nearly all thrown down, but the strong canoe was
uninjured, although no common boat could have withstood the shock.
Having determined to go up the river in this boat, we took
provisions with us for the voyage, and one of the negroes agreed to
act as cook. Having arranged everything, and breakfasted with my
kind friends, Mr. and Mrs. Hollenbeck, I bade them adieu, and
settled myself into the small space in the canoe that I expected to
occupy for six days. Captain Anderson took the helm, the "Caribs"
dipped their paddles into the water, and away we glided into a
narrow channel amongst long grass and rushes that almost touched us
on either side. Greytown, with its neat white houses, and feathery
palms, and large-leaved bread-fruit trees, was soon shut from our
view, and our boatmen plying their paddles with the greatest
dexterity and force, made the canoe shoot along through the still
water. Soon we emerged into a wider channel where a stronger stream
was running, and then we coasted along close to the shore to avoid
the strength of the current. The banks at first were low and marshy
and intersected by numerous channels; the principal tree was a
long, coarse-leaved palm, and there were great beds of wild cane
and grass, amongst which we occasionally saw curious green lizards,
with leaf-like expansions (like those on the leaf-insects),
assimilating them in appearance to the vegetation amongst which
they sought their prey. As we proceeded up the river, the banks
gradually became higher and drier, and we passed some small
plantations of bananas and plantains made in clearings in the
forest, which now consisted of a great variety of dicotyledonous
trees with many tall, graceful palms; the undergrowth being ferns,
small palms, Melastomae, Heliconiae, etc. The houses at the
plantations were mostly miserable thatched huts with scarcely any
furniture, the owners passing their time swinging in dirty
hammocks, and occasionally taking down a canoe-load of plantains to
Greytown for sale. It is one of the rarest sights to see any of
these squatters at work. Their plantain patch and occasionally some
fish from the river suffice to keep them alive and indolent.
At seven o'clock we reached the Colorado branch, which carries off
the greater part of the waters of the San Juan to the sea. This is
about twenty miles above Greytown, but only eighteen by the
Colorado to the sea, and is near the head of the delta, as I have
already mentioned. The main body of water formerly flowed down past
Greytown, and kept the harbour there open, but a few years ago,
during a heavy flood, the river greatly enlarged and deepened the
entrance to the Colorado Channel, and since then year by year the
Greytown harbour has been silting up. Now (I am writing in 1873)
there is twelve feet of water on the bar at the Colorado in the
height of the dry season, whilst at Greytown the outlet of the
river is sometimes closed altogether. The merchants at Greytown
have entertained the project of dredging out the channel again, but
now that the river has found a nearer way to the sea by the
Colorado this would be a herculean task, and it would cost much
less money to move the whole town to the Colorado, where by
dredging the bar a fine harbour might easily be made, but
unfortunately the Colorado is in Costa Rica, the Greytown branch in
Nicaragua, and there are constant bickerings between the two states
respecting the outlet of this fine river, which make any
well-considered scheme for the improvement of it impracticable at
present. A sensible solution of the difficulty would be a
federation of the two small republics. The heads of the political
parties in the two countries see, however, in this a danger to
their petty ambitions, and will not risk the step, and so the
boundary question remains an open one, threatening at any moment to
plunge the two countries into an impoverishing war.
If the Colorado were not to be interfered with by man, it would, in
the course of ages, carry down great quantities of mud, sand, and
trunks of trees, and gradually form sandbanks at its mouth, pushing
out the delta further and further at this point, until it was
greatly in advance of the rest of the coast; the river would then
break through again by some nearer channel, and the Colorado would
be silted up as the Lower San Juan is being at present. The
numerous half filled-up channels and long lagoons throughout the
delta show the various courses the river has at different times
taken.
Our boatmen paddled on until nine o'clock, when we anchored in the
middle of the stream, which was here about one hundred yards wide.
Distant as we were from the shore, we were not too far for the
mosquitoes, which came off in myriads to the banquet upon our
blood. Sleep for me was impossible, and to add to the discomfort,
the rain came down in torrents. We had an old tarpaulin with us,
but it was full of holes, and let in the water in little streams,
so that I was soon soaked to the skin. Altogether, with the
streaming wet and the mosquitoes, it was one of the most
uncomfortable nights I have ever passed.
The waning moon was sufficiently high at four o'clock to allow us
to bring the long dreary night to an end, and to commence paddling
up the river again. As the day broke the rain ceased, the mists
cleared away, our spirits revived, and we forgot our discomforts of
the night in admiration of the beauties of the river. The banks
were hidden by a curtain of creeping and twining plants, many of
which bore beautiful flowers, and the green was further varied here
and there by the white stems of the cecropia trees. Now and then we
passed more open spots, affording glimpses into the forest, where
grew, in the dark shade, slender-stemmed palms and beautiful
tree-ferns, contrasting with the great leaves of the Heliconiae. At
seven we breakfasted on a sand-bank, and got our clothes and
blankets dried. There were numerous tracks of alligators, but it
was too early to look for their eggs in the sand; a month later, in
March, when the river falls, they are found in abundance, and eaten
by the canoe-men. At noon we reached the point where the Seripiqui,
a river coming down from the interior of Costa Rica, joins the San
Juan about thirty miles above Greytown. The Seripiqui is navigable
by canoes for about twenty miles from this point, and then
commences a rough mountain mule-track to San Jose, the capital of
Costa Rica. We paddled on all the afternoon with little change in
the river. At eight we anchored for the night, and although it
rained heavily again, I was better prepared for it, and, coiling
myself up under an umbrella beneath the tarpaulin, managed to sleep
a little.
We started again before daylight, and at ten stopped at a small
clearing for breakfast. I strolled back a little way into the
gloomy forest, but it was not easy to get along on account of the
undergrowth and numerous climbing plants that bound it together. I
saw one of the large olive-green and brown mot-mots (Momotus
martii), sitting upon a branch of a tree, moving its long curious
tail from side to side, until it was nearly at right angles to its
body. I afterwards saw other species in the forests and savannahs
of Chontales. They all have several characters in common, linked
together in a series of gradations. One of these features is a spot
of black feathers on the breast. In some species this is edged with
blue, in others, as in the one mentioned above, these black
feathers form only a small black spot nearly hidden amongst the
rust-coloured feathers of the breast. Characters such as these,
very conspicuous in some species, shading off in others through
various gradations to insignificance, if not extinction, are known
by naturalists to occur in numerous genera; and so far they have
only been explained on the supposition of the descent of the
different species from a common progenitor.
(PLATE 3. HEADS OF MOT-MOTS.)
As I returned to the boat, I crossed a column of the army or
foraging ants, many of them dragging along the legs and mangled
bodies of insects that they had captured in their foray. I
afterwards often encountered these ants in the forests and it may
be convenient to place together all the facts I learnt respecting
them.
ECITONS, OR FORAGING ANTS.
The Ecitons, or foraging ants, are very numerous throughout Central
America. Whilst the leaf-cutting ants are entirely vegetable
feeders, the foraging ants are hunters, and live solely on insects
or other prey; and it is a curious analogy that, like the hunting
races of mankind, they have to change their hunting-grounds when
one is exhausted, and move on to another. In Nicaragua they are
generally called "Army Ants." One of the smaller species (Eciton
predator) used occasionally to visit our house, swarm over the
floors and walls, searching every cranny, and driving out the
cockroaches and spiders, many of which were caught, pulled or
bitten to pieces, and carried off. The individuals of this species
are of various sizes; the smallest measuring one and a quarter
lines, and the largest three lines, or a quarter of an inch.
I saw many large armies of this, or a closely allied species, in
the forest. My attention was generally first called to them by the
twittering of some small birds, belonging to several different
species, that follow the ants in the woods. On approaching to
ascertain the cause of this disturbance, a dense body of the ants,
three or four yards wide, and so numerous as to blacken the ground,
would be seen moving rapidly in one direction, examining every
cranny, and underneath every fallen leaf. On the flanks, and in
advance of the main body, smaller columns would be pushed out.
These smaller columns would generally first flush the cockroaches,
grasshoppers, and spiders. The pursued insects would rapidly make
off, but many, in their confusion and terror, would bound right
into the midst of the main body of ants. A grasshopper, finding
itself in the midst of its enemies, would give vigorous leaps, with
perhaps two or three of the ants clinging to its legs. Then it
would stop a moment to rest, and that moment would be fatal, for
the tiny foes would swarm over the prey, and after a few more
ineffectual struggles it would succumb to its fate, and soon be
bitten to pieces and carried off to the rear. The greatest catch of
the ants was, however, when they got amongst some fallen brushwood.
The cockroaches, spiders, and other insects, instead of running
right away, would ascend the fallen branches and remain there,
whilst the host of ants were occupying all the ground below. By and
by up would come some of the ants, following every branch, and
driving before them their prey to the ends of the small twigs, when
nothing remained for them but to leap, and they would alight in the
very throng of their foes, with the result of being certainly
caught and pulled to pieces. Many of the spiders would escape by
hanging suspended by a thread of silk from the branches, safe from
the foes that swarmed both above and below.
I noticed that spiders were generally most intelligent in escaping,
and did not, like the cockroaches and other insects, take shelter
in the first hiding-place they found, only to be driven out again,
or perhaps caught by the advancing army of ants. I have often seen
large spiders making off many yards in advance, and apparently
determined to put a good distance between themselves and their foe.
I once saw one of the false spiders, or harvest-men (Phalangidae),
standing in the midst of an army of ants, and with the greatest
circumspection and coolness lifting, one after the other, its long
legs, which supported its body above their reach. Sometimes as many
as five out of its eight legs would be lifted at once, and whenever
an ant approached one of those on which it stood, there was always
a clear space within reach to put down another, so as to be able to
hold up the threatened one out of danger.
I was much more surprised with the behaviour of a green, leaf-like
locust. This insect stood immovably amongst a host of ants, many of
which ran over its legs, without ever discovering there was food
within their reach. So fixed was its instinctive knowledge that its
safety depended on its immovability, that it allowed me to pick it
up and replace it amongst the ants without making a single effort
to escape. This species closely resembles a green leaf, and the
other senses, which in the Ecitons appear to be more acute than
that of sight, must have been completely deceived. It might easily
have escaped from the ants by using its wings, but it would only
have fallen into as great a danger, for the numerous birds that
accompany the army ants are ever on the look out for any insect
that may fly up, and the heavy flying locusts, grasshoppers, and
cockroaches have no chance of escape. Several species of
ant-thrushes always accompany the army ants in the forest. They do
not, however, feed on the ants, but on the insects they disturb.
Besides the ant-thrushes, trogons, creepers, and a variety of other
birds, are often seen on the branches of trees above where an ant
army is foraging below, pursuing and catching the insects that fly
up.
The insects caught by the ants are dismembered, and their too bulky
bodies bitten to pieces and carried off to the rear. Behind the
army there are always small columns engaged on this duty. I have
followed up these columns often; generally they led to dense masses
of impenetrable brushwood, but twice they led me to cracks in the
ground, down which the ants dragged their prey. These habitations
are only temporary, for in a few days not an ant would be seen in
the neighbourhood; all would have moved off to fresh
hunting-grounds.
Another much larger species of foraging ant (__Eciton hamata__) hunts
sometimes in dense armies, sometimes in columns, according to the
prey it may be after. When in columns, I found that it was
generally, if not always, in search of the nests of another ant
(Hypoclinea sp.), which rear their young in holes in rotten trunks
of fallen timber, and are very common in cleared places. The
Ecitons hunt about in columns, which branch off in various
directions. When a fallen log is reached, the column spreads out
over it, searching through all the holes and cracks. The workers
are of various sizes, and the smallest are here of use, for they
squeeze themselves into the narrowest holes, and search out their
prey in the furthest ramifications of the nests. When a nest of the
Hypoclinea is attacked, the ants rush out, carrying the larvae and
pupae in their jaws, only to be immediately despoiled of them by
the Ecitons, which are running about in every direction with great
swiftness. Whenever they come across a Hypoclinea carrying a larva
or pupa, they capture the burden so quickly, that I could never
ascertain exactly how it was done.
As soon as an Eciton gets hold of its prey, it rushes off back
along the advancing column, which is composed of two sets, one
hurrying forward, the other returning laden with their booty, but
all and always in the greatest haste and apparent hurry. About the
nest which they are harrying everything is confusion, Ecitons run
here and there and everywhere in the greatest haste and disorder;
but the result of all this apparent confusion is that scarcely a
single Hypoclinea gets away with a pupa or larva. I never saw the
Ecitons injure the Hypoclineas themselves, they were always
contented with despoiling them of their young. The ant that is
attacked is a very cowardly species, and never shows fight. I often
found it running about sipping at the glands of leaves, or milking
aphides, leaf-hoppers, or scale-insects that it found unattended by
other ants. On the approach of another, though of a much smaller
species, it would immediately run away. Probably this cowardly and
un-antly disposition has caused it to become the prey of the Eciton.
At any rate, I never saw the Ecitons attack the nest of other
species.
The moving columns of Ecitons are composed almost entirely of
workers of different sizes, but at intervals of two or three yards
there are larger and lighter-coloured individuals that will often
stop, and sometimes run a little backward, halting and touching
some of the ants with their antennae. They look like officers
giving orders and directing the march of the column.
This species is often met with in the forest, not in quest of one
particular form of prey, but hunting, like _Eciton predator_, only
spread out over a much greater space of ground. Crickets,
grasshoppers, scorpions, centipedes, wood-lice, cockroaches, and
spiders are driven out from below the fallen leaves and branches.
Many of them are caught by the ants; others that get away are
picked up by the numerous birds that accompany the ants, as
vultures follow the armies of the East. The ants send off exploring
parties up the trees, which hunt for nests of wasps, bees, and
probably birds. If they find any, they soon communicate the
intelligence to the army below, and a column is sent up immediately
to take possession of the prize. I have seen them pulling out the
larvae and pupae from the cells of a large wasp's nest, whilst the
wasps hovered about, powerless, before the multitude of the
invaders, to render any protection to their young.
I have no doubt that many birds have acquired instincts to combat
or avoid the great danger to which their young are exposed by the
attacks of these and other ants. Trogons, parrots, toucans,
mot-mots, and many other birds build in holes of trees or in the
ground, and these, with their heads ever turned to the only
entrance, are in the best possible position to pick off singly the
scouts when they approach, thus effectually preventing them from
carrying to the main army intelligence about the nest. Some of
these birds, and especially the toucans, have bills beautifully
adapted for picking up the ants before they reach the nest. Many of
the smaller birds build on the branches of the bull's-horn thorn,
which is always thickly covered with small stinging honey-eating
ants, that would not allow the Ecitons to ascend these trees.
Amongst the mammalia the opossums can convey their young out of
danger in their pouches, and the females of many of the tree-rats
and mice have a hard callosity near the teats, to which the young
cling with their milk teeth, and can be dragged away by the mother
to a place of safety.
The eyes in the Ecitons are very small, in some of the species
imperfect, and in others entirely absent; in this they differ
greatly from those ants which hunt singly, and which have the eyes
greatly developed. The imperfection of eyesight in the Ecitons is
an advantage to the community, and to their particular mode of
hunting. It keeps them together, and prevents individual ants from
starting off alone after objects that, if their eyesight were
better, they might discover at a distance. The Ecitons and most
other ants follow each other by scent, and, I believe, they can
communicate the presence of danger, of booty, or other
intelligence, to a distance by the different intensity or qualities
of the odours given off. I one day saw a column of __Eciton hamata__
running along the foot of a nearly perpendicular tramway cutting,
the side of which was about six feet high. At one point I noticed a
sort of assembly of about a dozen individuals that appeared in
consultation. Suddenly one ant left the conclave, and ran with
great speed up the perpendicular face of the cutting without
stopping. It was followed by others, which, however, did not keep
straight on like the first, but ran a short way, then returned,
then again followed a little further than the first time. They were
evidently scenting the trail of the pioneer, and making it
permanently recognisable. These ants followed the exact line taken
by the first one, although it was far out of sight. Wherever it had
made a slight detour they did so likewise. I scraped with my knife
a small portion of the clay on the trail, and the ants were
completely at fault for a time which way to go. Those ascending and
those descending stopped at the scraped portion, and made short
circuits until they hit the scented trail again, when all their
hesitation vanished, and they ran up and down it with the greatest
confidence. On gaining the top of the cutting, the ants entered
some brushwood suitable for hunting. In a very short space of time
the information was communicated to the ants below, and a dense
column rushed up to search for their prey.
The Ecitons are singular amongst the ants in this respect, that
they have no fixed habitations, but move on from one place to
another, as they exhaust the hunting grounds around them. I think
_Eciton hamata_ does not stay more than four or five days in one
place. I have sometimes come across the migratory columns. They may
easily be known by all the common workers moving in one direction,
many of them carrying the larvae and pupae carefully in their jaws.
Here and there one of the light-coloured officers moves backwards
and forwards directing the columns. Such a column is of enormous
length, and contains many thousands, if not millions of
individuals. I have sometimes followed them up for two or three
hundred yards without getting to the end.
They make their temporary habitations in hollow trees, and
sometimes underneath large fallen trunks that offer suitable
hollows. A nest that I came across in the latter situation was open
at one side. The ants were clustered together in a dense mass, like
a great swarm of bees, hanging from the roof, but reaching to the
ground below. Their innumerable long legs looked like brown threads
binding together the mass, which must have been at least a cubic
yard in bulk, and contained hundreds of thousands of individuals,
although many columns were outside, some bringing in the pupae of
ants, others the legs and dissected bodies of various insects. I
was surprised to see in this living nest tubular passages leading
down to the centre of the mass, kept open just as if it had been
formed of inorganic materials. Down these holes the ants who were
bringing in booty passed with their prey. I thrust a long stick
down to the centre of the cluster, and brought out clinging to it
many ants holding larvae and pupae, which probably were kept warm
by the crowding together of the ants. Besides the common
dark-coloured workers and light-coloured officers, I saw here many
still larger individuals with enormous jaws. These they go about
holding wide open in a threatening manner, and I found, contrary to
my expectation, that they could give a severe bite with them, and
that it was difficult to withdraw the jaws from the skin again.
One day when watching a small column of these ants, I placed a
little stone on one of the ants to secure it. The next that
approached, as soon as it discovered the situation of the prisoner,
ran backwards in an agitated manner, and communicated the
intelligence to the others. They rushed to the rescue, some bit at
the stone and tried to move it, others seized the captive by the
legs, and tugged with such force that I thought the legs would be
pulled off, but they persevered until they freed it. I next covered
one up with a piece of clay, leaving only the ends of its antennae
projecting. It was soon discovered by its fellows, which set to
work immediately, and by biting off pieces of the clay, soon
liberated it. Another time I found a very few of them passing along
at intervals. I confined one of these under a piece of clay, at a
little distance from the line, with his head projecting. Several
ants passed it, but at last one discovered it and tried to pull it
out, but could not. It immediately set off at a great rate, and I
thought it had deserted its comrade, but it had only gone for
assistance, for in a short time about a dozen ants came hurrying
up, evidently fully informed of the circumstances of the case, for
they made directly for their imprisoned comrade, and soon set him
free. I do not see how this action could be instinctive. It was
sympathetic help, such as man only among the higher mammalia shows.
The excitement and ardour with which they carried on their
unflagging exertions for the rescue of their comrade could not have
been greater if they had been human beings, and this to meet a
danger that can be only of the rarest occurrence. Amongst the ants
of Central America I place the Eciton as the first in intelligence,
and as such at the head of the Articulata. Wasps and bees come next
to ants, and then others of the Hymenoptera. Between ants and the
lower forms of insects there is a greater difference in reasoning
powers than there is between man and the lowest mammalian. A recent
writer has argued that of all animals ants approach nearest to man
in their social condition.* (*Houzeau, "Etudes sur les Facultes
mentales des Animaux comparees a celles de l'Homme.") Perhaps if we
could learn their wonderful language we should find that even in
their mental condition they also rank next to humanity.
I shall relate two more instances of the use of a reasoning faculty
in these ants. I once saw a wide column trying to pass along a
crumbling, nearly perpendicular, slope. They would have got very
slowly over it, and many of them would have fallen, but a number
having secured their hold, and reaching to each other, remained
stationary, and over them the main column passed. Another time they
were crossing a water-course along a small branch, not thicker than
a goose-quill. They widened this natural bridge to three times its
width by a number of ants clinging to it and to each other on each
side, over which the column passed three or four deep. Except for
this expedient they would have had to pass over in single file, and
treble the time would have been consumed. Can it not be contended
that such insects are able to determine by reasoning powers which
is the best way of doing a thing, and that their actions are guided
by thought and reflection? This view is much strengthened by the
fact that the cerebral ganglia in ants are more developed than in
any other insect, and that in all the Hymenoptera, at the head of
which they stand, "they are many times larger than in the less
intelligent orders, such as beetles."* (* Darwin, "Descent of Man"
volume 1 page 145.)
The Hymenoptera standing at the head of the Articulata, and the
Mammalia at the head of the Vertebrata, it is curious to mark how,
in geological history, the appearance and development of these two
orders (culminating, one in the Ants; the other in the Primates)
run parallel. The Hymenoptera and the Mammalia both make their
first appearance early in the secondary period, and it is not until
the commencement of the tertiary epoch that ants and monkeys appear
upon the scene. There the parallel ends. No one species of ant has
attained any great superiority above all its fellows, whilst man is
very far in advance of all the other Primates.
When we see these intelligent insects dwelling together in orderly
communities of many thousands of individuals, their social
instincts developed to a high degree of perfection, making their
marches with the regularity of disciplined troops, showing
ingenuity in the crossing of difficult places, assisting each other
in danger, defending their nests at the risk of their own lives,
communicating information rapidly to a great distance, making a
regular division of work, the whole community taking charge of the
rearing of the young, and all imbued with the strongest sense of
industry, each individual labouring not for itself alone but also
for its fellows--we may imagine that Sir Thomas More's description
of Utopia might have been applied with greater justice to such a
community than to any human society. "But in Utopia, where every
man has a right to everything, they do all know that if care is
taken to keep the public stores full, no private man can want
anything; for among them there is no unequal distribution, so that
no man is poor, nor in any necessity, and though no man has
anything, yet they are all rich; for what can make a man so rich as
to lead a serene and cheerful life, free from anxieties, neither
apprehending want himself, nor vexed with the endless complaints of
his wife? He is not afraid of the misery of his children, nor is he
contriving how to raise a portion for his daughters, but is secure
in this, that both he and his wife, his children and grandchildren,
to as many generations as he can fancy, will all live both
plentifully and happily."