Ant parasites—Fleet-footed brigands—Honey-stealing mites—A
strange table companion—Privileged cockroaches—Ants and
their riders—A fly-ride on beetle-back.
LEAVING the beetles—though as there are probably some thousands that
live habitually in ants’ nests, we have said very little about them—we
may glance at an extraordinary little creature, in appearance something
like a wood-louse with a fish’s tail, that resides with certain ants on
the footing of a freebooter, constantly stealing from them, and eluding
their resentment by extreme activity, living, as it were, in a state of
perpetual motion. The legs of these persistent yet withal timid brigands
are many and long, which, together with their shape and general
lightness of build, enables them to run with great speed, so that they
easily outdistance the ants, and, escaping to some less frequented part
of the nest, with which they are always well acquainted, remain there
quiet for a time. Should a single ant approach them, however, they
immediately run away, or, if forced by circumstances to be near one or
more—which, in an ants’ nest, must be often difficult to avoid—make a
point, apparently, of never keeping still, as though to confuse them,
or, perhaps, to be the better able to dash off at any instant.
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[Illustration: AN INSECT FREEBOOTER, AND AN INSECT BEGGAR.]
The extraordinary looking insect shown towards the top is the
lepismid, or fleet-foot, who lives by stealing food from
ants when they are in the act of passing it from one to the
other. The atemeles beetle shown below is begging food,
which will not be refused, from the ant in front of him.
The way in which these fleet-foots secure their food is highly
remarkable, each little theft—which has about it more of the parasite
than the brigand—occasioning a group of three. The ants upon which they
live are of the species known as _Lasius umbratus_, and, like many other
kinds, often feed one another, the hungry asking of the full, by whom he
is rarely, if ever, denied. In the process of regurgitation—with which
we are now familiar—the two stand fronting each other, with mandibles
interlocked, and a drop of honey passes from mouth to mouth. For an
instant it trembles between the two, resting on both, and that instant
is the opportunity of the _Lepismid_. Darting forward, he interposes his
own, and having absorbed some portion of the drop _in transitu_, speeds
swiftly away to make a third elsewhere. Such a life, however great may
be the thief’s agility, is full of danger, and, from time to time, an
individual is captured and killed. In nests under observation such
executions may be witnessed, and _Lepismid_ corpses—or, as various
professors prefer calling them, _cadavers_—are sometimes noted. Under
artificial conditions, however, opportunities of escape are much more
limited, unless, indeed, some special provision is made. Thus, when
Professor Wheeler first introduced a colony of _Lasius umbratus_ into
one of his _formicariums_, he found, after a couple of _dies_,[12] five
_Lepismid cadavers_. But having, by the addition to the said
_formicarium_ of a _refugium_, or asylum, made it more as _in natura_,
this mortality ceased, and the remaining _Lepismids_ continued
henceforth _existentes_.
A similar mode of feeding, but under circumstances of much greater
security, is indulged in by _Antennophorus_, another ant-guest, whose
relations with its host are of a still closer description.
_Antennophorus_ is a mite which, according to M. Janet, fixes itself on
to the head, or the sides of the abdomen, of the ant which it affects,
and clings there as long as it sees fit. This it is enabled to do owing
to a special adaptation of the feet, which end in little horny cups
(_cornicula_ is the word here) furnished with some substance of so
adhesive a quality that it might well be called “stickphast,” if no
Latin word were at hand. Not all the feet, however, are of this
description, for the anterior ones are transformed into a pair of long
waving antennæ, which contain olfactory organs of the greatest
sensibility. With these their owner makes up for the want of eyes, and,
smelling and feeling its way, walks, when it wishes to, along the bodies
of its hosts, passing from one to another. Sometimes, either by accident
or otherwise, it becomes detached, and is then helpless as far as
locomotion is concerned, but by no means so in other respects. Its
object, now, is to reaffix itself: nor is it long before it succeeds in
doing so. As it “lies upon the soil in one of the galleries of the nest
it raises and stretches forward its first pair of ambulatory feet, and,
at the same time, explores the space around it with its long antenniform
ones. These appendages are much more agitated when an ant passes close
by. Should it pass near enough, the _Acarid_ (which has a finer sound
than ‘mite’) glues itself on to its body by means of the cup of sticky
material at the end of one of its ambulatory feet, which it holds up
ready for this operation, and it can, in this way, soon climb up and fix
itself in a good position on its host. The latter is surprised, and
seeks to rid itself of its strange companion, but failing in this, it
becomes resigned very quickly (as we do to increased taxation) as soon
as the _Acarid_ has taken up one of its normal positions.”[13] It will
carry two indeed, or even three, without complaining. An ant with one of
these burdens fixed, like the income-tax, to the under side of its head,
and two others, which may stand for a rise in tea and sugar, is a very
common sight.
The feeding of _Antennophorus_ has been closely observed by M. Janet in
his artificial nests, and is thus described by him: “The ants had
acquired a habit of placing themselves, crowded one against another, in
one corner of the nest, and thither came such as had their crops well
filled, after a meal of honey, and disgorged it before the mouths of
their comrades who had none. While the fasting ant was eating the honey
thus disgorged, _Antennophorus_, riding on its head, took its share. To
do this, it pushed itself forward, and thrust its rostrum into the
droplet, and generally, whilst holding itself in position by means of
the two hinder pairs of legs, it attached itself by means of the forward
pair (which in this case, however, would represent antennæ) to the head
of the disgorging ant.”[13] Perhaps there is some little mistake
here—possibly I have not copied the passage correctly. There has been no
hint before as to the modified antenniform legs of the parasite
performing any other office than that of feeling and smelling, whilst
the word “attach” or “affix” is that always used to describe the working
of the sticky, cup-footed ones. In the position described the antennæ
might very well act as supports, but hardly, one would think, in such a
way as that their owner could be described as attaching himself through
their means. Possibly it is the first pair of true legs that act in this
way, but the matter is of no great consequence—not more than a war, say,
or the fall of a ministry, in the general run of things. Suffice it that
we have our picture, the little parasite stretched, like a bridge,
between the heads of the feeding and disgorging ants, and taking its
share with the latter.
_Lasius something_ is the name of the ant which _Antennophorus_ utilises
in this way, and it is, I think, a European species. Another
one—_Pachycondyla harpax_—the large, black ant of America—wears its
parasite round its neck, like an Elizabethan ruff. In this case both
host and guest are in the larval state, and the involuntary partnership
between them—involuntary probably on the part of either—is not dissolved
until both have attained full maturity. The position of affairs is this:
the ant larva apparently lies on its back upon earth a little hollowed,
to receive it, by the workers of the nest. The parasitic larva—that of
an unknown species of fly—has a long, slender neck, as we may call the
anterior part of the body, and whilst this is wound about the
corresponding portion of its host, the body, which broadens out after
the manner of an oil-flask, is affixed by a disc at its end to some part
of the back of the latter. When the ants feed the larvæ, they place the
food—which consists either of grain that has been stored, or of insects
captured and torn up by them—on the broad surface of the abdomen, which
forms a sort of trough for its reception. Immediately upon feeling the
welcome load, the hungry larva stretches down its head to the banquet,
but that of the parasite moves with it, and its small, sharp jaws take
eager toll of each dish. Thus the two feed together, cheek by jowl, and
should what has been provided prove insufficient for this double
onslaught, the unbidden guest will stretch its snake-like neck, and move
it ceaselessly until the ever-ready jaws come into contact with a second
feast, upon the table next it. Should none, however, be within reach,
the guest will give vent to its irritated feelings by biting the bodies
of such unbounteous Timons, or even that of its own host. They wriggle
with pain, and this may possibly induce the ants to bring them fresh
supplies, under the impression that they are hungry, as indeed they may
be, with meals shared in this way. If so, we can hardly suppose a
parasitic larva to act with such a motive, but as the best biters would
in this case get the most food, natural selection may possibly have
helped to develop the habit, which would have a compensating advantage
for the wrigglers too. As the French say, “_Il y a compensation en
tout._”
The parasite, whilst stretching out as far as it can from the body of
its host, in quest of food, remains, all the while, attached to the
latter by the disc in which its body ends. It can, however, leave one
ant larva for another, though Professor Wheeler, to whom we owe this
interesting discovery, believes that it does this “with great
reluctance, and only under urgent circumstances, such as extreme hunger,
the death of the larva to which it is attached, and perhaps, when fully
mature, and about to pupate.”[14] So long, indeed, as its original host,
on whose body, when quite young, it was probably hatched from the egg,
continues well and is well fed, it has no reason to seek farther, since
all its wants are provided for. It is not only fed by the worker ants,
but shares in any other of the benefits which these may bestow upon the
rising generation of the nest. Thus, if they move larvæ, as is
customary, to give them change of temperature, and produce the requisite
hygienic conditions, the parasite is moved along with them, and it is
cleaned also—a still more important advantage possibly—at the same time
as they are. At such times the ants never seem to notice the uncouth
incubus upon the bodies of their infant sisters, though one would
suppose the difficulty would be not to do so. They are, it is true,
blind, or nearly so, but it seems strange that their sense of touch,
which is no doubt delicate, should not be able to inform them, since the
parasite, though small enough, absolutely, is of great size regarded as
an excrescence on its host’s body. This probably is the way in which the
matter presents itself to the ants, if they think about it at all, for
since the two lives are passed constantly together, and are subjected to
the same conditions, it is likely that they share one smell between
them.
But this curious parasitic relation between ant and fly is not confined
to the larval stage of each. Continued observation led to a further
discovery which I give in Professor Wheeler’s own words: “As the days
passed, the mature ant-larvæ spun their brown cocoons one by one, and
one by one the mature commensals (the larval parasites, that is to say)
disappeared. No traces of them could be discovered. The only remaining
resource was to open the cocoons. Five were opened, and in two of recent
formation commensals were found! Having shared the table of their host,
they had come to share its bed as well. The dipteron (the parasite, as I
have said, is a fly) had pupated after the manner of its kind, forming a
puparium, that is, instead of spinning a cocoon like the ant larva: the
dead larval skin, somewhat shrivelled and contracted, was used as an
envelope, and within this the pupa proper was found. In all cases the
puparium was located in the caudal pole (at the bottom) of the ant
cocoon, and was immovably stuck to the wall of the cocoon, its anterior
end directed towards the cephalic pole”[14] (the top). But what, asks
Professor Wheeler, does the commensal larva do “while the ant-larva is
weaving its cocoon? Does it move about to avoid the swaying jaws of the
spinning larva? or does it take up its position, from the first, at the
posterior end of the larval ant, and there remain motionless while the
posterior pole of the cocoon is being completed? It is very difficult to
answer these questions.”[14]
One might think that young ants thus deprived, day by day, of a portion
of every meal, would be stunted in their growth, and not make such large
and healthy workers as those who had never been encumbered with a
parasite. This, however, does not seem to be the case, and no difference
can be detected between the one and the other. Perhaps, therefore, ants
habitually eat, if not more than is good for them, at least more than
they require. This is the case almost universally amongst civilised men,
at least in Northern Europe, and with savages to a still greater extent
whenever the wherewithal is at hand. In the above case we have, as
Professor Wheeler remarks, a very perfect example of what is termed
commensalism, in the original meaning of the word—that is to say, of two
or more individuals dining together at the same table. As applied to
natural history, the individuals in question must be of different
species, but it is not often that the definition otherwise is so
rigorously adhered to.
This curious parasite inhabits the nests, or, more strictly speaking,
the bodies, of an ant, native to Texas, that has long been famous as a
storer of grain, but whose supposed still further achievements in an
agricultural direction would now seem open to doubt. In the nest of
another American ant, which most certainly does grow mushrooms, the same
observer found another “_myrmecophile_,” or ants’ nest insect, viz. a
minute species of cockroach that lives its life amongst the caves and
galleries of the great vegetable mass which forms, and is designed to
form, the mushroom bed, upon the product of which it feeds. Here again
the ants have become thoroughly reconciled to the presence amongst them
of a guest from which, as far as can be seen, they derive no benefit,
whilst having to submit to a loss, through its agency, of some part of
the fruits of their labours. These little cockroaches are fairly
numerous, and have become so adapted to living in darkness that their
eyes have almost disappeared. Another loss, or partial loss, is of a
more curious nature, and, one might think, would be a great privation to
them. Their antennæ, namely, are always incomplete, but this does not
seem to have come about by a gradual process of atrophy, but rather to
have been caused by mutilation during their owners’ lifetime. But how
has this happened, and what has been the mutilating agency? Professor
Wheeler’s explanation, which he believes to be the only one, is that
their antennæ have been unconsciously sheared off by the ants, whilst
engaged either in clipping their mushrooms or in cutting up the pieces
of leaves which they are continually bringing into the nest, to add to
the bed on which they grow. “It is easy,” he says, “to understand how an
insect like a cockroach, living in the midst of thousands of ants which
are continually opening and closing their scissor-like mandibles, should
be certain, sooner or later, to have its long antennæ cropped. One
wonders how the tarsi (the legs, that is to say) of the cockroach escape
the same treatment.”[15] This wonder, however, if there is really any
reason for it, suggests a doubt as to the sufficiency of the explanation
here offered. The antennæ, one would think, might be held high, in which
case, if sheared at all, it could only be at the base, but if here (as
would not, however, seem to be the case) why should not the legs be
sheared too? Again, it seems possible that the insects themselves may be
in the habit of gnawing one another’s antennæ. As the cockroaches live
and flourish it would seem that this mutilation of their antennæ, if
that, indeed, be the explanation, can do them no great injury. Yet these
organs are supposed to be of great importance to insects, and, judging
by their length and delicacy, one would think that they were especially
so to the members of the cockroach family. In this case they would
probably be extremely careful of them, and the fact that these
ants’-nest cockroaches do not seem to be so, may show that subterranean
conditions, contrary to what one might have expected, have affected
their efficacy.
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[Illustration: A RIDE ON BEETLE-BACK, AND A LIVING SWEET-SHOP.]
Enjoyment seems to be the only motive the fly has for riding
on the back of the African beetle shown in the upper part of
this illustration. Beneath is shown the well named honey-pot
ant with its distended body full of honey, which it gives
away to any hungry working ant.
A diet of mushrooms, or fungus, is not the only thing for which these
little blind, light-shunning cockroaches are indebted to their
landlords, the ants, for often one of them may be seen to mount upon one
of the latter, and take a ride on its back. They seem especially fond of
the soldiers, as horses, and will sit perched on their enormous heads,
as they walk up and down in a stately sort of way, sometimes for quite a
long time. Enjoyment seems here to be the only motive, and perhaps it is
a natural one, since there is a fly in Africa which seems to have quite
a passion for riding on the back of a beetle. “Across the mouth of the
Seyhouse,” says the Rev. Mr. Eaton, “on sandy pasture-land bordering the
seashore, big _coprophagous_ beetles—it sounds abusive, but no harm is
meant—are common, sheltering in large holes in the soil, when at rest,
and running about on business. A small species of _Borborinæ_ (that is
the fly) may often be seen riding on their backs, chiefly on the
pronotum and about the bases of the elytra, sometimes half a dozen
females on one beetle. The beetles occasionally throw themselves on
their backs, and try to get rid of them by rolling; but the flies elude
all their efforts to dislodge them, dodging out of harm’s way into the
jointures of the thorax, and darting from back to breast, and back
again, in a way that drives the beetle nearly mad. In vain she scrapes
over them with her legs, in vain does she roll over, or delve down
amongst the roots of the herbage: the flies are as active as monkeys
(not perhaps a very striking simile here), and there is no shaking them
off. It is difficult (such is their strange predilection) to get them
off into the killing-bottle. Nothing (not even the killing-bottle)
persuades them to fly, and they would very much rather stick to the
beetle than——” what? Not go to heaven, but “be driven off it down the
tube.”[16] The tube must be the neck of that same bottle. This, surely,
is a case of infatuation if ever there was one. Eccentric fly! And what
must be the charms of a beetle that can prevail over those of cyanide of
potassium! But the beetle, it must be remembered, is a _coprophagous_
one. There may be a world of explanation in a word like that.
-----
Footnote 12:
If _cadaver_ for corpse or carcase, why not _dies_ for day, which is
just as good English? Or why not all Latin, with a glossary, or—better
still—a translation?
Footnote 13:
Charles Janet, _Comptes Rendus_, 1897, pp. 583-5.
Footnote 14:
The American Naturalist, December, 1901.
Footnote 15:
Ibid., November, 1900.
Footnote 16:
The Entomologist’s Monthly Magazine (quoted in the _American
Naturalist_), August, 1896.
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