THE LEGIONARY ANTS
These insects, which Wheeler describes as “the Huns and Tartars of the
insect world,” are found in tropical Africa and Asia, and in the warmer
parts of America. There is a great variation in size and appearance
between the different castes, the females and workers being blind and
wingless, while the males have well developed wings and large compound
eyes. Some of these ants have no fixed habitation, but wander from
place to place, traveling mostly at night, and camping during the day
in any shallow hole that affords a temporary shelter. They cannot
endure the direct rays of the sun, and Savage, in 1845, observed that
“if they should be detained abroad till late in the morning of a
sunny day by the quantity of their prey, they will construct arches
over their path, of dirt agglutinated by a fluid excreted from the
mouth,” except when they can remain concealed by thick grass or leaves.
Sometimes the soldier ants form a sort of network arch with their own
bodies, and Savage says that “whenever an alarm is given the arch is
instantly broken, and the ants, joining others of the same class on
the outside of the line, who seem to be acting as commanders, guards
and scouts, run about in a furious manner in pursuit of the enemy.
If the alarm should prove without foundation, the victory won or the
danger passed, the arch is quickly renewed, and the main column marches
forward as before in all the order of a military discipline.”
In these marches the ants carry their eggs, larvae and pupae with them,
these being borne in the mandibles of the _minima_ or small workers,
and the whole column lives by foraging. Savage’s description of their
predatory habits is well worth quoting here: “They will soon kill the
largest animal if confined. They attack lizards, guanas, snakes, etc.,
with complete success. We have lost several animals by them--monkeys,
pigs, fowl, etc. The severity of their bite is increased to great
intensity by vast numbers, to a degree impossible to conceive. We may
easily believe that it would prove fatal to any animal in confinement.
They have been known to destroy the _Python natalensis_, our largest
serpent. When gorged with prey it lies motionless for days; then,
monster as it is, it easily becomes their victim.... Their entrance
into a house is soon known by the simultaneous and universal movement
of rats, mice, lizards, Blapsidae, Blattidae, and of the numerous other
vermin that infest our dwellings. Not being agreed, they cannot dwell
together, which modifies in a good measure the severity of the driver’s
habits, and renders their visits sometimes (though very seldom in my
view) desirable. Their ascent into our beds we sometimes prevent by
placing the feet of the bedsteads into a basin of vinegar, or some
other uncongenial fluid; this will generally be successful if the
rooms are ceiled, or the floors overhead tight; otherwise they will
drop down upon us, bringing along with them their noxious prey in the
very act of contending for victory. They move over the house with a
good degree of order, ransacking one point after another, till, either
having found something desirable, they collect upon it, when they may
be destroyed _en masse_ by hot water; or, disappointed, they abandon
the premises as a barren spot, and seek some other more promising
locality for exploration. When they are fairly in we give up the house,
and try to await with patience their pleasure, thankful, indeed, if
permitted to remain within the narrow limits of our beds or chairs.
They are decidedly carnivorous in their propensities. Fresh meat of all
kinds is their favorite food; fresh oils also they love, especially
that of _Elais guiniensis_, either in the fruit or expressed. Under my
observation they pass by milk, sugar and pastry of all kinds, also salt
meat; the latter, when boiled, they have eaten, but not with the zest
of fresh. It is an incorrect statement, often made, that _they devour
everything eatable_ by us in our houses; there are many articles which
form an exception. If a heap of rubbish comes within their route, they
invariably explore it, when larvae and insects of all orders are borne
off in triumph--especially the former.”
Sometimes, instead of camping in shelters on the ground, these ants
climb up into a tree and hang together in a cluster like a swarm of
bees. Savage reports a colony suspended from a low tree: “From the
lower limbs (four feet high) were festoons or lines of the size of
a man’s thumb, reaching to the plants and ground below, consisting
entirely of these insects; others were ascending and descending upon
them, thus holding free and ready communication with the lower and
upper portions of this dense mass. One of these festoons I saw in the
act of formation; it was a good way advanced when first observed:
ant after ant coming down from above, extending their long limbs and
opening wide their jaws, gradually lengthened out the living chain till
it touched the broad leaf of a _Canna coccinea_ below. It now swung to
and fro in the wind, the terminal ant meanwhile endeavoring to attach
it by his jaws and legs to the leaf; not succeeding, another ant of the
same class (the very largest) was seen to ascend the plant, and, fixing
his hind legs with the apex of the abdomen firmly to the leaf under the
vibrating column, then reaching with his fore-legs and opening wide his
jaws, closed in with his companion above, and thus completed the most
curious ladder in the world.”
Similar chains are used in bridging little rills or even small brooks,
but when a real flood occurs a different procedure is adopted. In this
case they cling together so as to form a large ball, with the eggs and
young in the center, and float away upon the water until a safe landing
can be effected.
There are several kinds of legionary and driver ants in America; some
species have been found as far north as Texas and even Colorado, but
most of them are confined to the tropics. These ants usually do not
spend all of their time on the march, but have permanent nests, from
which they sally out at intervals on foraging expeditions. Belt offers
a graphic description of the sortie of a colony in Brazil: “One of the
smaller species (_Eciton praedator_) used occasionally to visit our
house, swarm over 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.... 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 followed the ants in the woods. On
approaching to ascertain the cause of the 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.... 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 of the ground below. By and by up would come some of the ants,
following every branch, and driving their prey before them to the ends
of the small twigs, when nothing remained for them but to leap, and
they would alight in the very midst 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.”
[Illustration: Fig. V. Legionary ants attacking a snake.]
Some of the Brazilian species are more nomadic in their habits.
Belt says: “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-colored 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
habitation in hollow trees, and sometimes underneath large fallen
trunks that offer suitable hollows. A nest I came across in the latter
situation was open at one side, and 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 insects. I was
surprised to see in this living nest tubular passages leading down
into the center of the mass, kept open just as if it had been formed
of inorganic material. Down these holes the ants who were bringing the
booty passed with their prey. I thrust a long stick down to the center
of the cluster and brought out clinging to it many ants holding larvae
and pupae, which were probably kept warm by the crowding together of
the ants. Besides the common dark-colored workers and light-colored
officers, I saw there 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.”
Sumichrast, who studied some of the Mexican legionaries in 1863,
noted many seemingly aimless migrations, “which they undertake at
undetermined epochs, but in relation, it appears to me, with the
atmospheric changes. What traveler, passing over the _tierra caliente_,
has not encountered the phalanxes of _tepeguas_ upon the paths of the
primitive forests? What inhabitant of these countries has not, at least
once, been unpleasantly torn from the arms of sleep by the invasion
of his domicile by a black army of _soldados_?... Besides the changes
of domicile which are so generally in relation with the atmospheric
variation as to serve as a rule to the inhabitants of the country,
the _Eciton_ devotes itself every season to excursions for pillage,
destined to supply the larvae with nourishment. Nothing is more
curious than these _battues_ executed by an entire population. Over an
extent of many square meters, the soil literally disappears under the
agglomeration of their little black bodies. No apparent order reigns in
the mass of the army, but behind this many lines or columns of laggards
press on to rejoin it. The insects concealed under the dry leaves and
the trunks of fallen trees fly on all sides before this phalanx of
pitiless hunters, but, blinded by fright, they fall back among their
persecutors and are seized and dispatched in the twinkling of an eye.
Grasshoppers, in spite of the advantage given them by their power of
leaping, hardly escape more easily. As soon as they are taken, the
_Eciton_ tears off the hinder feet and all resistance becomes useless.”
The same author describes with some feeling their habit of invading
houses. “These visits ordinarily take place at the beginning of the
rainy season, and almost always during the night. The expeditionary
army penetrates the habitation which it proposes to visit at many
points at once, and for this purpose divides itself into many columns
of attack. One is apprised very soon of their arrival by the household
commotion among the parasitic animals. The rats, the spiders, the
cockroaches, abandon their retreats and seek to escape from the attacks
of the ants by flight. Alimentary substances the _soldados_ hold in
no esteem, and they disdain even sugary things, to which the ants in
general are so partial. Dead insects even do not seem to invite their
covetousness. It has often happened to me to be obliged to abandon
my abode, without having time to carry away my collection, to which
they have never done the least injury. The trouble occasioned by these
insects in entering houses is more than compensated by the expeditious
manner in which they purge them of vermin, and in this view their visit
is an actual benefit.”
As these ants are usually quite blind and their movements are directed
(so far as we can tell) by the sense of smell and contact alone, it
is quite remarkable that they are able to move about so readily, and
become familiar with their surroundings in less time than their seeing
relatives. Forel wrote in 1899: “Throw a handful of _Ecitons_ with
their larvae on a spot with which they are absolutely unacquainted. In
such circumstances other ants scatter about in disorder and require an
hour or more to assemble and bring their brood together and especially
to become acquainted with their environment, but the _Ecitons_ do this
at once. In five minutes they have formed distinct files which no
longer disintegrate. They carry their larvae and pupae, marching in a
straight path, palpating the ground with their antennae and exploring
all the holes and crevices till they find a suitable retreat and enter
it with surprising order and promptitude. The workers follow one
another as if at a word of command, and in a very short time all are in
safety.”