AN ISLAND SETTLEMENT
OUR children often made themselves useful by reporting finds in the
shape of nests, and one day they returned from the island with a
wonderful tale of great numbers of big wasps that were digging in the
ground. “I don’t know what they are,” said the small boy, “but they act
to me like the maddest kind of hornets.” With this attractive picture
before us, we lost no time in going over to the spot, where we found
a thriving colony of Bembex spinolæ. On our approach they fell upon
us, “desire of blood, and rage, and lust of fight” in their mien, and
chased us to a distance, but without inflicting a single wound. This
temperance was not due to gentleness of disposition, but to the fact
that Bembex is not at all handy with her sting, her body being too
large and clumsy to curve and give the lightning stab as other wasps
do. With renewed courage we again approached them, more cautiously this
time, and soon learned that if we preserved an extremely composed and
dignified demeanor our presence on the field would be tolerated.
Bembex, like Philanthus, and some species of Sphex, lives in a sort of
semi–social state, a number of individuals occupying the same space
of ground, although each one has its separate nest. Bembex, however,
differs from these genera and from almost all of the solitary wasps in
her habit of feeding her young from day to day, or rather from hour to
hour, as long as it remains in the larval state. This difference in
her maternal cares as compared with those of other species results in
a less numerous progeny. The larva, for a period of two weeks, demands
constant attention from the mother, so that a second egg cannot be laid
until the first–born has gone into its cocoon, unless, indeed, she
feeds two larvæ at once, which does not seem probable. The season of
work is ten or twelve weeks, so that Wesenberg is probably correct in
allowing only five or six young ones to each mother for the summer.
In watching our wasps we found that the new nests were usually made
in the outskirts of the colony, which was thus continually extending
its limits. Like many other species, Bembex has great difficulty
in deciding just where to dig. Our Sphex made three beginnings
before finally settling down. The only Ammophila that we watched
from the beginning changed her place after working for ten minutes.
P. quinquenotatus often tried half a dozen places before she was
satisfied, and spinolæ is quite as difficult to please.
When, at last, the right place is found, the labor of excavation is
carried on vigorously. The mandibles are used for loosening the earth,
and for lifting, but the greater part of the work is done with the
first pair of legs, the tarsi of which are doubled up while the dirt is
swept out with the brush of stiff spiny hairs on the second joint. This
attitude gives them a very comical aspect, making them look as if they
were sweeping with their elbows. They sometimes lie far over to one
side while loosening the earth with their mandibles. While digging, the
body is held high by the straightening of the third pair of legs, and
the dirt comes out behind in a rapid stream, flying to a distance of
three or four inches. Before long the wasp is lost to sight, but every
few moments she comes backing out, pushing behind her the dirt that
she has displaced below. In about fifteen minutes the nest is ready,
and the wasp turns her attention to scattering all the dirt that has
been thrown out, sweeping the ground clean so that no sign of her work
remains. We have often speculated as to the meaning of the careful and
conscientious performance of this part of her task. With the wasps that
nest by themselves it is not easy to see what enemy they are providing
against in hiding the entrance to the nest; but the precaution seems
still less necessary—even absurd—in the Bembex field, where there is
no possibility of concealing the colony, and where the nests are only
an inch or two apart, so that an enemy might burrow anywhere with
the certainty of finding one. Moreover, the only enemy that we could
discover was the parasitic fly, which never attempts to enter when
the hole is closed. However, unmoved by our opinion on the subject,
spinolæ spends five or six minutes of her precious time in making the
neighborhood of her home quite tidy, and then she fills in the mouth of
the nest with a little loose earth before going away to catch her fly.
Oxybelus, though she is limited in choice by her small size, can
catch a fly in three or four minutes. Bembex is strong enough to take
anything that she sees, and she has no preference for one species
above another, yet she seldom finds one under twenty or twenty–five
minutes. When she comes back nothing of the fly is visible unless it
is unusually large, so closely is it held under her body by the second
pair of legs. She alights, and scratches away the loose earth at the
entrance of the nest with her first legs, and then, as she creeps
within, she passes the fly along from the second to the third pair, so
that the end of its body, projecting beyond the abdomen of the wasp,
is visible for an instant before it is carried inside. Sometimes she
drops the fly behind her, and then, turning around, pulls it in with
her mandibles. In other cases, where a longer portion of the tunnel has
been filled with earth, the fly is left lying on the ground while the
wasp clears the way. This offers a favorable opportunity to parasites,
especially as the fly is not placed with regard to its safety, but
is dropped anywhere. The dirt that is kicked out sometimes covers it
so that when the way is clear the careless proprietor must search it
out and clean it off before she can store it away. In one instance,
in which we had been opening a nest close by, the tunnel was entirely
blocked by the loose earth which we had disturbed, and the wasp worked
for ten minutes before she cleared a way to her nest. During part of
this time she held the fly, but when she realized that it was going to
be a long piece of work she laid it down near by. As the wasp enters
she sometimes leaves the hole open behind her, but oftener fills it by
pushing up earth from below. When she comes out again she throws in a
little dirt, and then begins to circle about the place. She seems not
quite easy about the nest, however, returning three or four times to
scratch earth over the entrance, before finally taking her departure.
We opened a good many nests in the course of the summer, and found
them all very much alike, much more so than is the case with other
species. The entrance tunnel runs in obliquely for from three to five
inches below the surface of the ground, and ends in a pocket.
We grow accustomed to marvels, and from our familiarity with other
wasps we take as a matter of course the unerring accuracy with which
Bembex swoops down upon the exact spot at which the entrance to her
nest is hidden. And yet how strange a power it is! There is not the
least sign to help her—not a stone, not a blade of grass is to be seen
on the field. Our method of marking a nest which we wished to find
again was to place tiny pebbles at exactly equal distances from it, one
on either side, so that the middle point of the straight line between
them gave us the desired spot; and the wasp doubtless uses the same
method, only her landmarks are sometimes so infinitesimal that we do
not recognize them.
Bouvier finds that when he cuts away the plants around the nest of B.
labiatus, clearing a space of twenty–eight or thirty inches square,
the wasp is much confused, flying about for a long time before she is
able to find her home. He once placed a flat stone over the entrance.
The wasp alighted upon it, and after scratching vainly for a while made
her way in. The stone was left in this position for two days, during
which time Bembex learned to regard it as a landmark, for upon its
being removed to a distance of eight inches she still followed it upon
returning with her fly, and insisted upon finding her nest near it.
[Illustration: NEST OF BEMBEX]
An observation of Marchand points to the same conclusion. He says:—
On July seventeenth, 1900, during a short sojourn at Pouliguen, on
returning from a hunt after Diptera and Hymenoptera in the cliffs of
Caudan, about eleven in the morning, in tropical heat, I paused to take
breath near the old mill of Caudan and looked about for a little shade
before continuing my walk to Pen–Château. I had seated myself on the
stones of a slope shaded from the sun and was wiping the perspiration
from my forehead, when I saw a large wasp arrive directly before me. I
instinctively followed it with my eyes; it paused some yards from the
mill on the side of the cliff, and began to open a nest which was placed
scarcely twenty inches from the foot of a swallow–wort, a rather common
plant in the neighborhood of the ruin. She was Bembex rostrata at work
at provisioning her nest.
Moved by curiosity, instead of going on to breakfast, I awaited the exit
from the nest, which took place in about five minutes. Bembex scratched
the sand and took flight from the side of the cliff. How long would she
be away? I looked at my watch and arose.
Ought I to go or to wait a little while? I took the latter decision. Out
of malice, and without any idea of trying a control experiment to the
admirable observations which science owes to the naturalist of Sérignan,
of whom I was not thinking at all, I cut close to the sand the stalk
of the swallow–wort and planted it a little nearer the mill, moving it
about two feet, and being careful to put in place of the plant a little
fragment of a bottle which I found in the mill. I seated myself in the
shade and waited. Twenty minutes later the wasp dropped straight on to
the place where I had cut the plant, that is to say, it deviated from
its nest by a distance about equal to the displacement to which I had
subjected the swallow–wort. It walked right and left, agitating its
antennæ, appearing confused as to the locality. I followed these goings
and comings for two or three minutes. Several times it flew away and
then returned, always searching about. Pitying it and desiring, since I
was now relieved of the fatigue which the heat had caused me, to go back
to breakfast, I took my net and drawing near, made as if to catch it,
swinging the pocket rapidly about. It veered away with a quick jerk of
the wings. I then took up the swallow–wort, lifting the fragment which
marked its original place, and replanted it in the sand.
I again looked at my watch to see whether I could consecrate yet a
few more minutes to curiosity without making my kind host, my friend
Dr. M^[ce] Rivron, and his wife, who honored me with the charming
hospitality of Kursac, wait too long. It was only half past eleven; we
usually did not breakfast until about noon; it would take only a quarter
of an hour to traverse the distance from the mill of Caudan to the
house. I could then, without fear of being chided, dispose of fifteen
minutes. This lapse of time would perhaps suffice to show me whether my
_bestiole_ would this time find the way to her nest without hesitation.
I waited a little; five minutes had not passed when my Bembex, coming
like an arrow, alighted on the sand near the plant, still holding the
prey which I had noticed when she departed at my chasing her, after
her vain attempts to find the entrance to her nest; but this time she
did not hunt long. She felt about a little to right and left, but soon
turned directly toward the entrance to the tunnel, distant scarcely two
inches from the place where she had settled. My Bembex had a memory.
A curious thing about these wasps, and one which shows how much common
feeling they have, is that they work in waves, all starting off on
their hunting expeditions within a few minutes of each other, and
returning together after the chase. At one time all the residents seem
to be present, digging their nests, carrying in their booty, dashing
at each other, and chasing the parasites with a tremendous amount of
humming and swooping about. Then suddenly they are all gone. Nothing
remains but multitudes of flies, which keep up a giddy dance over the
field, and for ten or fifteen minutes the place seems deserted. Then
the wasps begin to return, several coming at a time, and as if by magic
the whole scene awakens to life. More than half of the wasps bring
nothing home with them, and these fall to robbing their more fortunate
companions. Those that are carrying flies must pause a moment, burdened
as they are, to scratch away the earth at the entrance to the nest.
When unmolested they go in very quickly, but it is just at this point
that the marauders fall upon them, displaying an amount of persistence
and energy in their attacks that, were it properly directed, might
easily enable them to secure flies for themselves.
We once saw a wasp that had been fortunate enough, or perhaps
unfortunate enough, to catch an immense fly, the wings of which stood
out on both sides very conspicuously. This made her an especial mark
for her unprincipled relatives. Half a dozen of them chased her about,
like chickens pursuing one of their number that has found a worm. She
circled and settled, and circled and swooped around for five or six
minutes, continually pursued and attacked by the robbers, and quite
unable to get into her nest. At last, curious to see what she was
carrying, we made her drop her load, and secured it for ourselves.
We found it to be a horse fly, quite dead, but showing no marks of
violence. It was not wasted, for we afterward fed it to one of our wasp
nurslings at home.
At another time we saw one wasp attack another that was bringing in a
fly. In the struggle that ensued the owner lost her booty, as the two
rolled over and over on the ground, and as they parted it was seized by
the thief. They clinched again, and rolled on the ground as before, and
this time the fly was recovered by the rightful owner. At this point,
thinking that perhaps one of the wasps was a male, and that this might
be their style of courtship, we seized both of them; whereupon the fly
was dropped, and the two wasps turned their attention to attacking us.
Both proved to be females. Not only do the Bembecids fight in this way
for the possession of their prey—they quarrel even without apparent
cause. We have seen two females digging their nests at a little
distance apart, one of which was repeatedly attacked by the other,
although she did nothing to provoke the aggressor. They are certainly
very unneighborly, and have no idea of living in harmony. When flying
in a threatening manner, either at us or at each other, they have a way
of wagging their abdomens violently from side to side in a way well
calculated to inspire terror.
In warm sunny weather spinolæ works industriously through the middle
of the day, and seems determined to provide abundantly, not only for
her own offspring, but for any unbidden guests that it may be her
fate to care for. She never works more than four or five hours a day,
however, and in unfavorable weather she does not work at all. On going
over to the island one cloudy morning to spend some hours in watching
the Bembex activities, we found the spot quiet and lifeless. No one
seeing it for the first time would have dreamed of the multitudes of
living creatures beneath his feet. The nests seemed to be all closed,
but on peering curiously about we found one on sloping ground, in the
suburbs of the colony, of which the door was open. Just within was
the proprietor gazing out on the landscape, as she is shown in the
illustration. She seemed to be leaning on her elbows, and her face,
enlivened by two great goggle eyes, had an irresistibly comical
aspect. With the exception of the omnipresent flies, this wasp was
the only sign of life about the place. Even in good weather, and in
working hours, the wasps sometimes rest, for we have seen them go in
empty–handed, closing the door behind them, to remain for half an hour
at a time.
[Illustration: BEMBEX SPINOLÆ LOOKING OUT OF NEST]
There is one thought that must strike even a casual observer at the
sight of the hordes of parasites that hover over a Bembex colony:—
“The buzzing flies, a persevering train,
Incessant swarm, and chased return again.”
Why do not these wasps, fly–catchers as they are by profession, kill
the worthless wretches that infest their homes, thriving abundantly on
the fruits of their labor, a continual menace to the life and safety
of their offspring? To the uninitiated it would seem that these flies
might serve as food for the wasp larvæ quite as well as any of the
dozen species that they actually take; but even if the wasp–mother
believes that they possess indigestible qualities, it would be much
less trouble to kill them and throw them away than to be perpetually
chasing them to a little distance only to see them return as soon as
she gives her attention to anything else. Whatever the reason for it
may be, the relation between the wasps and the flies is certainly most
curious and puzzling. Fabre’s explanation is that since this miserable
little fly has its own part to play in nature, Bembex must respect it,
thus preserving harmony in the world of living things. The idea is
perfectly in accord with his own theories, but we find ourselves quite
unable to accept it.
There can be no doubt that the parasites are a grave danger to Bembex.
She suffers from them far more than any other wasp that we are
familiar with, her mode of feeding the young rendering her peculiarly
susceptible to their attacks. Of the ten or twelve nests that we
opened only one was free from them, the others containing from two
to five lively maggots nearly as large as the wasp larvæ, which were
sharing the food brought in by the mother. Fabre, who has studied the
question thoroughly, has found as many as ten parasitic larvæ in one
nest. He has also noticed that where the parasites are most numerous
the wasp–larva is proportionately small and emaciated, reaching only
one half or one third of its normal size. When it attempts to spin
its cocoon it has not strength enough to do so, and thus perishes
miserably among the pupæ of the interlopers, which have the advantage
of developing more rapidly. He has proved, by experiments upon nests
transported to his study, that although the invaders preserve friendly
relations with the rightful owner of the nest so long as food is
abundant, they nevertheless, at the first suggestion of scarcity, fall
upon the wasp larva and ruthlessly devour it. This “black action” he
has seen with his own eyes. In view of this base ingratitude, we are
more than ever impressed with the troubles of the poor Bembex mother,
as she tries to feed a dozen mouths where she has bargained for only
one.
We several times saw a fly follow a wasp into her nest, remaining
within for half a minute, and it is probable that they go in to lay
their eggs. According to Fabre, it is the habit of the flies that are
parasitic upon the half–dozen species of Bembex that he has studied
to seize the moment at which the fly projects from under the abdomen
of the wasp as she enters the nest; and he has even known them to lay
two or three eggs on one fly in the instant of time that its body was
exposed.
Fabre took a partly grown Bembex larva from the nest, where it was
surrounded by the remains of twenty flies. He fed it generously, and it
ate sixty–two more, making a total of eighty–two in the eight days that
passed before the spinning of the cocoon. Our experiments in this line
gave similar results. We took charge of a partly grown larva on the
afternoon of August tenth, and between that date and August fifteenth,
when it spun its cocoon, it ate forty–two house flies besides a big
Tabanus.
Fabre thinks that under natural conditions the mother does not give
the larva all it can eat at one time, but provides it with what she
considers a reasonable amount of food, and keeps anything that she
catches beyond this out of its reach. He draws his conclusion from the
fact that he has found several flies in the tunnel leading to the nest,
while the larva had as many more close to it. It would certainly be
convenient for Bembex to have a reserve of this kind in case of rainy
weather, but the forethought implied in such an action seems to require
a higher degree of intelligence than can be claimed for her.
In one nest we found a single fly with a long cylindrical egg attached
to the left side of the thorax just at the origin of the third leg. In
another, which we had seen made and provisioned, we found, six days
later, a larva which we judged to be four days old. Assuming that the
egg was laid on the first day, it must have taken it about two days
to hatch. Other nests gave us larvæ in all stages of development,
surrounded by the remains of Diptera, among which Syrphus, Tabanus, and
Musca were represented.
In regard to the condition of the flies captured by Bembex, we have
never seen the crushing of the thorax, which is noted by both Wesenberg
and Fabre. Indeed, the flies that we found were not always dead, since
in two instances they responded readily to stimulation. Similar results
have been obtained by Mr. S. W. Dunning of Hartford, Connecticut.
Twice we have seen our spinolæ, as she was bringing home her prey,
alight near the nest and sting it as it was held with the second pair
of legs. We could see the process distinctly, since she is slow and
clumsy, and, in one instance, had difficulty in reaching the fly,
falling over to one side in an awkward manner. It is probable, then,
that this is a habit with the wasp, but that the sting is usually given
at the place of capture.
We opened a number of Bembex nests, but succeeded in raising only one
larva, which we took when it was half grown. This one, during the five
days that passed before it spun the cocoon, ate forty–three flies.
Mr. Bates has some notes on Monedula signata, which takes nothing but
flies, and even confines itself to a single species, although it must
sometimes go half a mile away to find it. This reminds us of Pompilus
quinquenotatus, which never takes anything but Epeira strix.
[Illustration: BEMBEX]
A considerable contribution to our knowledge of the genus Bembex has
been made in the paper by Wesenberg (written in Danish) which has
already been referred to. This paper deals with Bembex rostrata. It was
translated for Mr. Ashmead by Mr. Martin Linell.
[Illustration: A CORNER OF THE BEMBEX COLONY]
It seems that rostrata makes its nest in solid sand, covering it up
with loose sand, and usually, also, with a little flat stone, to
prevent parasites from entering. The cell measures one cubic inch, the
entrance tunnel being one and one half centimeters long, and arcuate. A
cell contains four or five fresh flies (Lucilia, Eristalis, etc.), and
torn–off wings, sucked–out thoraces, and in the middle of these, a big
flat larva.
When the larva is hatched the mother brings more and more flies, the
flies being larger and larger as it grows. This adjustment of the size
of the fly to the growth of the larva has also been noted by Fabre.
Wesenberg says that fifty Bembecids will nest on a spot as big as
a room during a period of three months. The time required for the
development of the larva is two weeks, this giving five or six young
ones for the season. He queries, “Does each female have more than one
nest? and if so, how can she remember them?” To determine this point
we marked six wasps by touching them with differently colored paints,
putting near their nests pebbles painted to correspond with the owners,
and then watched them closely for three hours. During this time the
red wasp returned regularly to the red nest, the blue to the blue, and
so on. They were watched for an hour and a half on the following day
with the same result, so that it seems quite certain that spinolæ has
only one nest at a time. To feed two larvæ at once, with interlopers
thrown in, would be a heavier task than the most determined industry
could accomplish.