Santo Domingo. Many made papery nests, hanging from the undersides of
large leaves. Others hung their open cells underneath verandahs and
eaves of houses. One large black one was particularly abundant about
houses, and many people got stung by them. They also built their
pendent nests in the orange and lime trees, and it is not always safe
to gather the fruit. Fortunately they are heavy flyers, and can often
be struck down or evaded in their attacks. They do good where there
are gardens, as they feed their young on caterpillars, and are
continually hunting for them. Another species, banded brown and yellow
(_Polistes carnifex_), has similar habits but is not so common.
Bates, in his account of the habits of the sand-wasps at Santarem, on
the Amazon, gives an interesting account of the way in which they took
a few turns in the air around the hole they had made in the sand
before leaving to seek for flies in the forest, apparently to mark
well the position of the burrow, so that on their return they might
find it without difficulty. He remarks that this precaution would be
said to be instinctive, but that the instinct is no mysterious and
unintelligible agent, but a mental process in each individual
differing from the same in man only by its unerring certainty. I had
an opportunity of confirming his account of the proceedings of wasps
when quitting a locality to which they wished to return, in all but
their unerring certainty. I could not help noting how similar they
were to the way in which a man would act who wished to return to some
spot not easily found out, and with which he was not previously
acquainted. A specimen of the _Polistes carnifex_ was hunting about
for caterpillars in my garden. I found one about an inch long, and
held it out towards it on the point of a stick. It seized it
immediately, and commenced biting it from head to tail, soon reducing
the soft body to a mass of pulp. It rolled up about one-half of it
into a ball, and prepared to carry it off. Being at the time amidst a
thick mass of a fine-leaved climbing plant, before flying away, he
took note of the place where it was leaving the other half. To do
this, it hovered in front of it for a few seconds, then took small
circles in front of it, then larger ones round the whole plant. I
thought it had gone, but it returned again, and had another look at
the opening in the dense foliage down which the other half of the
caterpillar lay. It then flew away, but must have left its burden for
distribution with its comrades at the nest, for it returned in less
than two minutes, and making one circle around the bush, descended to
the opening, alighted on a leaf, and ran inside. The green remnant of
the caterpillar was lying on another leaf inside, but not connected
with the one on which the wasp alighted, so that in running in it
missed it, and soon got hopelessly lost in the thick foliage. Coming
out again, it took another circle, and pounced down on the same spot
again, as soon as it came opposite to it. Three small seed-pods, which
here grew close together, formed the marks that I had myself taken to
note the place, and these the wasp seemed also to have taken as its
guide, for it flew directly down to them, and ran inside; but the
small leaf on which the fragment of caterpillar lay, not being
directly connected with any on the outside, it again missed it, and
again got far away from the object of its search. It then flew out
again, and the same process was repeated again and again. Always when
in circling round it came in sight of the seed-pods down it pounced,
alighted near them, and recommenced its quest on foot. I was surprised
at its perseverance, and thought it would have given up the search;
but not so, it returned at least half a dozen times, and seemed to get
angry, hurrying about with buzzing wings. At last it stumbled across
its prey, seized it eagerly, and as there was nothing more to come
back for, flew straight off to its nest, without taking any further
note of the locality. Such an action is not the result of blind
instinct, but of a thinking mind: and it is wonderful to see an insect
so differently constructed using a mental process similar to that of
man. It is suggestive of the probability of many of the actions of
insects that we ascribe to instinct being the result of the possession
of reasoning powers.
[Illustration: WASP AND HOLE IN THE SAND.]
A WASP AND ITS PREY
(FROM THE INSTINCTS AND HABITS OF THE SOLITARY WASPS.)[6]
BY G. W. AND E. G. PECKHAM.
[6] Reprinted by permission from Bulletin No. 2, Series I, of The
Wisconsin Geological and Natural History Survey, 1898.
[Illustration]
Most graceful and attractive of all the wasps--as Fabre describes
them, the Ammophiles, of all the inhabitants of the garden, hold the
first place in our affections. Not so beautiful as the blue
_Pelopaeus_ nor so industrious as the little red-girdled _Trypoxylon_,
their intelligence, their distinct individuality, and their obliging
tolerance of our society make them an unfailing source of interest.
They are, moreover, the most remarkable of all genera in their
stinging habits, and few things have given us deeper pleasure than
our success in following the activities and penetrating the secrets of
their lives. In our neighborhood we have but two species of
_Ammophila_, _urnaria_ Cresson and _gracilis_ Cresson, both of them
being very slender bodied wasps of about an inch in length, _gracilis_
all black, and _urnaria_ with a red band around the front end of the
abdomen. With two exceptions our observations relate to _urnaria_.
During the earlier part of the summer we had often seen these wasps
feeding upon the nectar of flowers, especially upon that of the sorrel
of which they are particularly fond, but at that time we gave them but
passing notice. One bright morning in the middle of July, however, we
came upon one that was so evidently hunting, and hunting in earnest,
that we gave up everything else to follow her. The ground was covered,
more or less thickly, with patches of purslane, and it was under these
weeds that our _Ammophila_ was eagerly searching for her prey. After
thoroughly investigating one plant she would pass to another, running
three or four steps and then bounding as though she were made of
thistledown and were too light to remain upon the ground. We followed
her easily, and as she was in full view nearly all of the time we had
every hope of witnessing the capture, but in this we were destined to
disappointment. We had been in attendance on her for about a quarter
of an hour when, after disappearing for a few moments under the thick
purslane leaves, she came out with a green caterpillar. We had missed
the wonderful sight of the paralyzer at work, but we had no time to
bemoan our loss for she was making off at so rapid a pace that we were
well occupied in keeping up with her. She hurried along with the same
motion as before, unembarrassed by the weight of her victim. Twice she
dropped it and circled over it a moment before taking it again. For
sixty feet she kept to open ground, passing between two rows of
bushes, but at the end of this division of the garden, she plunged,
very much to our dismay, into a field of standing corn. Here we had
great difficulty in following her, since far from keeping to her
former orderly course, she zigzagged among the plants in the most
bewildering fashion, although keeping a general direction of
northeast. It seemed quite impossible that she could know where she
was going. The corn rose to a height of six feet all around us; the
ground was uniform in appearance, and, to our eyes, each group of corn
stalks was just like every other group, and yet, without pause or
hesitation, the little creature passed quickly along, as we might
through the familiar streets of our native town.
[Illustration: "She Hurried along, Unembarrassed by the Weight of Her
Victim."]
At last she paused and laid her burden down. Ah! the power that has
led her is not a blind, mechanically perfect instinct, for she has
travelled a little too far. She must go back one row into the open
space that she has already crossed, although not just at this point.
Nothing like a nest is visible to us. The surface of the ground looks
all alike, and it is with exclamations of wonder that we see our
little guide lift two pellets of earth which have served as a covering
to a small opening running down into the ground.
The way being thus prepared she hurries back with her wings quivering
and her whole manner betokening joyful triumph at the completion of
her task. We, in the meantime, have become as much excited over the
matter as she is herself. She picks up the caterpillar, brings it to
the mouth of the burrow and lays it down. Then, backing in herself,
she catches it in her mandibles and drags it out of sight, leaving us
full of admiration and delight.
How clear and accurate must be the observing powers of these wonderful
little creatures! Every patch of ground must, for them, have its own
character; a pebble here, a larger stone there, a trifling tuft of
grass--these must be their landmarks. And the wonder of it is that
their interest in each nest is so temporary. A burrow is dug,
provisioned and closed up, all in two or three days, and then another
is made in a new place with everything to learn over again.
From this time (July thirteenth) on to the first of September our
garden was full of these wasps, and they never lost their fascination
for us, although owing to a decided difference between their taste and
ours as to what constituted pleasant weather all our knowledge of them
was gained by the sweat of our brows. When we wished to utilize the
cool hours of the morning or of the late afternoon in studying them,
or thought to take advantage of a cloud which cast a grateful shade
over the sun at noonday, where were our Ammophiles? Out of sight
entirely, or at best only to be seen idling about on the flowers of
the onion or sorrel. At such a time they seemed to have no mission in
life and no idea of duty. But when the air was clear and bright and
the mercury rose higher and higher, all was changed. Their favorite
working hours were from eleven in the morning to three in the
afternoon, and when they did work they threw their whole souls into
it. It was well that it was so, for they certainly needed all the
enthusiasm and perseverance that they could muster for such wearisome
and disappointing labor. Hour after hour was passed in search, and
often there was nothing to show at the end of it, for, since the
caterpillars that they wanted were nocturnal species, most of them
were under ground in the day-time. The species observed by Fabre knew,
by some subtle instinct, where to find the worm, and unearthed it from
its burrow. _Urnaria_, on the contrary, never dug for her prey, but
hunted on bare ground, on the purslane, and most of all on the
bean-plants. These were examined carefully, the wasp going up and down
the stems and looking under every leaf, but the search was so
frequently unsuccessful that in estimating their work we are inclined
to think that they can scarcely average one caterpillar a day. When
they were hunting over bare ground they often paused and seemed to
listen, and in the beginning we expected to see them burrow down and
drag a victim from under the soil, but this never happened.
In this species, as in every one that we have studied, we have a most
interesting variation among the different individuals, not only in
methods but in character and intellect. While one was beguiled from
her hunting by every sorrel blossom she passed, another stuck to her
work with indefatigable perseverance. While one stung her caterpillar
so carelessly and made her nest in so shiftless a way that her young
could only survive through some lucky chance, another devoted herself
to these duties, not only with conscientious thoroughness, but with an
apparent craving after artistic perfection that was touching to see.
The method employed by the _Ammophilae_ in stinging their prey is more
complex than that of any other predatory wasp. The larvae with which
they provision their nests are made up of thirteen segments, and each
of these has its own nervous centre or ganglion. Hence if the
caterpillar is to be reduced to a state of immobility, or to state so
nearly approaching immobility that the egg may be safely laid upon it,
a single sting, such as is given by some of the _Pompilidae_ to their
captured spiders, will be scarcely sufficient. All this we knew from
Fabre's "Souvenirs," and yet we were not at all prepared to believe
that any plain American wasp could supply us with such a thrilling
performance as that of the Gallic _hirsuta_, which he so dramatically
describes. We were, however, most anxious to be present at the
all-important moment that we might see for ourselves just how and
where _Ammophila urnaria_ stings her victim.
For a whole week of scorching summer weather we lived in the bean
patch, scorning fatigue. We quoted to each other the example of
Fabre's daughter Claire, whose determination to solve the problem of
_Odynerus_ led to a sun-stroke. We followed scores of wasps as they
hunted; we ran, we threw ourselves upon the ground, we scrambled along
on our hands and knees in our desperate endeavors to keep them in
view, and yet they escaped us. After we had kept one in sight for an
hour or more some sudden flight would carry her far away and all our
labor was lost.
At last, however, our day came. We were doing a little hunting on our
own account, hoping to find some larvae which we could drop in view of
the wasps and thus lead them to display their powers, when we saw an
_urnaria_ fly up from the ground to the underside of a bean leaf and
knock down a small green caterpillar. Breathless with an excitement
which will be understood by those who have tasted the joy of such a
moment, we hung over the actors in our little drama. The ground was
bare, we were close by and could see every motion distinctly. Nothing
more perfect could have been desired.
The wasp attacked at once but was rudely repulsed, the caterpillar
rolling and unrolling itself rapidly and with the most violent
contortions of the whole body. Again and again its adversary descended
but failed to gain a hold. The caterpillar in its struggles, flung
itself here and there over the ground, and had there been any grass or
other covering near by it might have reached a place of partial
safety, but there was no shelter within reach, and at the fifth attack
the wasp succeeded in alighting over it, near the anterior end, and in
grasping its body firmly in her mandibles. Standing high on her long
legs and disregarding the continued struggles of her victim, she
lifted it from the ground, curved her abdomen under its body, and
darted her sting between the third and fourth segments. From this
instant there was a complete cessation of movement on the part of the
unfortunate caterpillar. Limp and helpless, it could offer no further
opposition to the will of its conqueror. For some moments the wasp
remained motionless, and then, withdrawing her sting, she plunged it
successively between the third and the second, and between the second
and the first segments.
[Illustration: WASP PLUNGING HER STING INTO THE CATERPILLAR.]
The caterpillar was now left lying on the ground. For a moment the
wasp circled above it and then, descending, seized it again, further
back this time, and with great deliberation and nicety of action gave
it four more stings, beginning between the ninth and tenth segments
and progressing backward.
_Urnaria_, probably feeling--as we certainly did--reaction from the
strain of the last few minutes, and a relief at the completion of her
task, now rested from her labors. Standing on the ground close by she
proceeded to smooth her body with her long hind legs, standing in the
meantime, almost on her head, with her abdomen directed upward. She
then gave her face a thorough washing and rubbing with her first
legs, and not until she had made a complete and satisfactory toilet
did she return to the caterpillar.
We saw _Ammophila_ capture her prey only three times during the whole
summer, but from these observations and from the condition of her
caterpillars taken at various times from nests, her method seems to be
wonderfully close to that of _hirsuta_, with just about the same
amount of variation in different individuals.
Thus in our second example, she stung the first three segments in the
regular order, the third, the second, and lastly (and most
persistently) the first. She then went on, without a pause, to sting
the fourth, fifth, sixth, and seventh, stopping at this point and
leaving the posterior segments untouched. In our first example, it
will be remembered, the middle segments were spared. The sting being
completed, she proceeded to the process known as _malaxation_, which
consists in repeatedly squeezing the neck of the caterpillar, or other
victim, between the mandibles, the subject of the treatment being
turned around and around so that all sides may be equally affected.
In our third case a caterpillar which we had caught was placed in
front of a wasp just after she had carried the second larva into her
nest. She seemed rather indifferent to it, passing it once or twice as
she ran about, but finally picked it up and gave it one prolonged
sting between the third and fourth segments. She then spent a long
time in squeezing the neck, pinching it again and again. It was then
left on the ground, and as she showed no further interest in it we
carried it home for further study.
In the three captures, then, that came under our observation, all the
caterpillars being of the same species and almost exactly of the same
size, three different methods were employed. In the first, seven
stings were given at the extremities, the middle segments being left
untouched, and no malaxation was practised. In the second, seven
stings again but given in the anterior and middle segments, followed
by slight malaxation. In the third, only one sting was given but the
malaxation was prolonged and severe.
[Illustration]
LEAF-CUTTING ANTS
(FROM THE NATURALIST IN NICARAGUA.)
BY THOMAS G. BELT, F.G.S.
[Illustration]
Nearly all travellers in tropical America have described the ravages
of the leaf-cutting ants (_OEcodoma_); their crowded, well-worn paths
through the forests, their ceaseless pertinacity in the spoliation of
the trees--more particularly of introduced species--which are left
bare and ragged, with the mid-ribs and a few jagged points of the
leaves only left. Many a young plantation of orange, mango, and lemon
trees has been destroyed by them. Again and again have I been told in
Nicaragua, when inquiring why no fruit-trees were grown at particular
places, "It is no use planting them; the ants eat them up." The first
acquaintance a stranger generally makes with them is on encountering
their paths on the outskirts of the forest crowded with the ants; one
lot carrying off the pieces of leaves, each piece about the size of a
sixpence, and held up vertically between the jaws of the ant; another
lot hurrying along in an opposite direction empty handed, but eager to
get loaded with their leafy burdens. If he follows this last division,
it will lead him to some young trees or shrubs, up which the ants
mount; and where each one, stationing itself on the edge of a leaf,
commences to make a circular cut, with its scissor-like jaws, from the
edge, its hinder-feet being the centre on which it turns. When the
piece is nearly cut off, it is still stationed upon it, and it looks
as though it would fall to the ground with it; but, on being finally
detached, the ant is generally found to have hold of the leaf with one
foot, and soon righting itself, and arranging its burden to its
satisfaction, it sets off at once on its return. Following it again,
it is seen to join a throng of others, each laden like itself, and,
without a moment's delay, it hurries along the well-worn path. As it
proceeds, other paths, each thronged with busy workers, come in from
the sides, until the main road often gets to be seven or eight inches
broad, and more thronged than the streets of the city of London.
[Illustration: SETS OFF AT ONCE ON ITS RETURN.]
After travelling for some hundreds of yards, often for more than half
a mile, the formicarium is reached. It consists of low, wide mounds of
brown, clayey-looking earth, above and immediately around which the
bushes have been killed by their buds and leaves having been
persistently bitten off as they attempted to grow after their first
defoliation. Under high trees in the thick forest the ants do not make
their nests, because, I believe, the ventilation of their underground
galleries, about which they are very particular, would be interfered
with, and perhaps to avoid the drip from the trees. It is on the
outskirts of the forest, or around clearings, or near wide roads that
let in the sun, that these formicariums are generally found. Numerous
round tunnels, varying from half an inch to seven or eight inches in
diameter, lead down through the mounds of earth; and many more, from
some distance around, also lead underneath them. At some of the holes
on the mounds ants will be seen busily at work, bringing up little
pellets of earth from below, and casting them down on the
ever-increasing mounds, so that its surface is nearly always fresh and
new-looking.
Standing near the mounds, one sees from every point of the compass
ant-paths leading to them, all thronged with the busy workers carrying
their leafy burdens. As far as the eye can distinguish their tiny
forms, troops upon troops of leaves are moving up towards the central
point, and disappearing down the numerous tunnelled passages. The
outgoing, empty-handed hosts are partly concealed amongst the bulky
burdens of the incomers, and can only be distinguished by looking
closely amongst them. The ceaseless, toiling hosts impress one with
their power, and one asks--What forests can stand before such
invaders? How is it that vegetation is not eaten off the face of the
earth? Surely nowhere but in the tropics, where the recuperative
powers of nature are immense and ever active, could such devastation
be withstood.
Further acquaintance with the subject will teach the inquirer that,
just as many insects are preserved by being distasteful to
insectivorous birds, so very many of the forest trees are protected
from the ravages of the ants by their leaves either being distasteful
to them, or unfitted for the purpose for which they are required,
whilst some have special means of defence against their attacks.
These ants do not confine themselves to leaves, but also carry off any
vegetable substance that they find suitable for growing the fungus on.
They are very partial to the inside white rind of oranges, and I have
also seen them cutting up and carrying off the flowers of certain
shrubs, the leaves of which they neglected. They are very particular
about the ventilation of their underground chambers, and have numerous
holes leading up to the surface from them. These they open out or
close up, apparently to keep up a regular degree of temperature below.
The great care they take that the pieces of leaves they carry into the
nest should be neither too dry nor too damp, is also consistent with
the idea that the object is the growth of a fungus that requires
particular conditions of temperature and moisture to ensure its
vigorous growth. If a sudden shower should come on, the ants do not
carry the wet pieces into the burrows, but throw them down near the
entrances. Should the weather clear up again, these pieces are picked
up when nearly dried, and taken inside; should the rain, however,
continue, they get sodden down into the ground, and are left there. On
the contrary, in dry and hot weather, when the leaves would get dried
up before they could be conveyed to the nest, the ants, when in
exposed situations, do not go out at all during the hot hours, but
bring in their leafy burdens in the cool of the day and during the
night. As soon as the pieces of leaves are carried in they must be cut
up by the small class of workers into little pieces. I have never seen
the smallest class of ants carrying in leaves! their duties appear to
be inside, cutting them up into smaller fragments, and nursing the
immature ants. I have, however, seen them running out along the paths
with the others; but instead of helping to carry in the burdens, they
climb on the top of the pieces which are being carried along by the
middle-sized workers, and so get a ride home again. It is very
probable that they take a run out merely for air and exercise. The
largest class of what are called workers are, I believe, the directors
and protectors of the others. They are never seen out of the nest,
excepting on particular occasions, such as the migrations of the ants,
and when one of the working columns or nests is attacked, they then
come stalking up, and attack the enemy with their strong jaws.
Sometimes, when digging into the burrows, one of these giants has
unperceived climbed up my dress, and the first intimation of his
presence has been the burying of his jaws in my neck, from which he
would not fail to draw blood. The stately observant way in which they
stalk about, and their great size, compared with the others, always
impressed me with the idea that in their bulky heads lay the brains
that directed the community in their various duties. Many of their
actions, such as that I have mentioned of two relays of workmen
carrying out the ant food, can scarcely be blind instinct. Some of the
ants make mistakes, and carry in unsuitable leaves. Thus grass is
always rejected by them, but I have seen some ants, perhaps young
ones, carrying leaves of grass; but after a while these pieces are
always brought out again and thrown away. I can imagine a young ant
getting a severe ear-wigging from one of the major-domos for its
stupidity.
[Illustration: SECTION THROUGH LEAF-CUTTING ANT'S NEST.]
I shall conclude this long account of the leaf-cutting ants with one
more instance of their reasoning powers.
A nest was made near one of our tramways, and to get to the trees the
ants had to cross the rails, over which the wagons were continually
passing and repassing. Every time they came along a number of ants
were crushed to death. They persevered in crossing for some time, but
at last set to work and tunnelled underneath each rail. One day, when
the wagons were not running, I stopped up the tunnels with stones; but
although great numbers carrying leaves were thus cut off from the
nest, they would not cross the rails, but set to work making fresh
tunnels underneath them. Apparently an order had gone forth, or a
general understanding been come to, that the rails were not to be
crossed.
[Illustration]
SOME WONDERFUL SPIDERS
(FROM A JOURNAL OF RESEARCHES, ETC.)
BY CHARLES DARWIN.
[Illustration]