THE GREAT GOLDEN DIGGER
THIS wasp (Sphex ichneumonea Linn.) is one of our most beautiful
species, its great size and its brilliant color, as it flies among the
flowers, serving to make it well known to all observers of nature.
During the later part of July, all through August, and even in the
early days of September it is commonly found at work making or storing
its burrow. It is rare in our garden, however, and we thought ourselves
fortunate in being able to keep track of one individual from the
making to the closing of the nest. Although large and powerful it is
gracefully formed. In color it is brown, varied with bright yellow.
On the morning of the third of August, at a little after ten o’clock,
we saw one of these hunters start to dig a nest on the side of a stony
hill. After making some progress in the work she flew off and selected
a second place, where she dug so persistently that we felt confident
that this was to be her final resting–place; but when the hole was two
and one half inches deep, it too was deserted. Again our wasp chose
a spot and began to burrow. She worked very rapidly, and at twenty
minutes before twelve the hole was three inches deep. At high noon she
flew away, and was gone forty minutes. The day was excessively hot,
about 98° Fahr., and we ourselves were only deterred from taking a
noonday rest by our fixed determination not to leave the place until we
had seen all that there was to be seen in the manœuvres of ichneumonea.
On returning she appeared very much excited, fairly quivering with
vitality as she resumed her work. She came up backward, carrying the
earth with her mouth and anterior legs, and went back from the opening
some little distance, when it was dropped, and she at once went in
again. While in the burrow we could hear her humming, just as the
Pelopæi do when, head downward in the wet mud, they gather their loads
for nest–building. In five or six trips a little mass of earth would
accumulate, and then she would lie quite flat on the heap and kick the
particles away in all directions. As the work progressed the earth was
carried further and further away before it was placed on the ground,
and as she backed in different directions the material brought out was
well spread about from the down–hill side of the nest. Sometimes she
would spend several moments in smoothing the débris all around, so
that the opening presented much the appearance of an immense ant–hill,
only the particles were much larger. During the first hour that we
watched her she frequently turned directly toward us, and, sometimes
remaining on the ground and sometimes rising on her wings to a level
with our faces, appeared to be eyeing us intently for four or five
seconds. Her attitude was comical, and she seemed to be saying, “Well,
what are you hanging around here for?”
[Illustration: THOROUGH LOCALITY STUDY BY SPHEX]
As the afternoon wore on she worked more calmly and her fidgety and
excited manner disappeared, the excavation progressing steadily until
half–past three. At that time she came out and walked slowly about in
front of her nest and all around it. Then she rose and circled just
above it, gradually widening her flight, now going further afield and
now flying in and out among the plants and bushes in the immediate
vicinity. The detailed survey of every little object near her nest was
remarkable; and not until her tour of observation had carried her five
times entirely around the spot did she appear satisfied and fly away.
All her actions showed that she was studying the locality and getting
her bearings before taking her departure. A fact that impressed us very
much was that with the two nests that she had begun and then deserted
she had taken no such precaution, but simply came up and flew off.
Had she made up her mind, if we may be allowed to use the term, that
the localities were in some way unsuitable and that hence she had no
occasion to return to them? Had she decided, in the last instance, that
she would return and so must get her bearings? We wondered how far the
different acts were instinctive, or were, as Huber has it, an evidence
of a “little dose of judgment.” Bates, in speaking of Monedula signata,
says that he often noticed it taking a few turns about the locality
of its nest, and that he was convinced that it was doing so for the
purpose of getting its bearings. Belt, having described how he fed a
specimen of Polistes carnifex with a caterpillar, which the wasp cut
into two parts, goes on to say: “Being at the time amidst a thick mass
of fine–leaved climbing plant, it proceeded, before flying away, to
take 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 around 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.”[2] He then remarks that when the wasp came back for the remaining
half it flew straight to its nest without taking any further note of
the locality. Both of these writers believe that many of the actions
of insects that are ascribed to instinct are really evidence of the
possession of a certain amount of intelligence.
[Illustration: HASTY LOCALITY STUDY BY SPHEX]
To return to our Sphex. When she flew away we naturally supposed that
she had gone in search of her prey, and we were on the _qui vive_ to
observe every step in her actions when she came home. Alas! when she
came back half an hour later, she was empty–handed. She dug for four
minutes, then flew off and was gone two minutes, then returned and
worked for thirty–five minutes. Another two minutes’ excursion, and
then she settled down to work in good earnest and brought up load
after load of earth until the shadows grew long. We noticed that on
these later trips she flew directly away, depending upon her first
careful study of the surroundings to find her way back. At fifteen
minutes after five the patient worker came to the surface, and made a
second study, this time not so detailed, of the environment. She flew
this way and that, in and out among the plants, high and low, far and
near, and at last, satisfied, rose in circles, higher and higher, and
disappeared from view. We waited for her return with all the patience
at our command, from fifteen minutes after five until fifteen minutes
before seven. We felt sure that when she came back she would bring her
victim with her, and when we saw her approaching we threw ourselves
prone on the ground, eagerly expecting to see the end of the drama; but
her search had been unsuccessful,—she carried nothing. In the realms
of wasp–life, disappointments are not uncommon, and this time she had
us to share her chagrin, for we felt as tired and discouraged as she
perhaps did herself. When we saw her entering without any provision
for her future offspring, we were at a loss what to do next; and it
may be that this state of mind was shared by her also, for she at once
began to fill in the entrance to her nest. We now thought it time to
act, and decided to capture her, to keep her over night in one of our
wasp–cages, and to try to induce her to return to her duty on the
following day. We therefore secured her in a large bottle, carried her
to the cottage, and having made every possible arrangement for her
comfort, left her for the night.
[Illustration: SPHEX DRAGGING GRASSHOPPER TO HER NEST]
On the next morning, at half after eight o’clock, we took Lady Sphex
down to her home, and placed the mouth of the bottle so that when she
came out she had to enter the nest. This she did, remaining below,
however, only a moment. When she came up to the surface she stood still
and looked about for a few seconds, and then flew away. It surprised
us that having been absent from the place for so many hours, she made
no study of the locality as she had done before. We thought it a very
unpromising sign, and had great fears that she was deserting the place
and that we should see her no more. One would need to watch a wasp
through the long hours of a broiling hot day to appreciate the joy
that we felt when at nine o’clock we saw her coming back. She had no
difficulty in finding her nest, nor did she feel any hesitation as to
what ought to be done next, but fell to work at once at carrying out
more dirt. The weather, although still hot, had become cloudy and so
threatening that we expected a down–pour of rain every moment, but
this seemed to make no difference to her. Load after load was brought
up, until, at the end of an hour, everything seemed completed to her
satisfaction. She came to the entrance and flew about, now this way,
and now that, repeating the locality study in the most thorough manner,
and then went away. At the expiration of an hour we saw her approaching
with a large light green meadow–grasshopper, which was held in the
mouth and supported by the fore legs, which were folded under. On
arriving, the prey was placed, head first, near the entrance, while the
wasp went in, probably to reassure herself that all was right. Soon
she appeared at the door of the nest and remained motionless for some
moments, gazing intently at her treasure. Then seizing it (we thought
by an antenna) she dragged it head first into the tunnel.
The laying of the egg did not detain her long. She was up in a moment
and began at once to throw earth into the nest. After a little she went
in herself, and we could plainly hear her humming as she pushed the
loose material down with her head. When she resumed the work outside we
interrupted her to catch a little fly that we had already driven off
several times just as it was about to enter the nest. The Sphex was
disturbed and flew away, and this gave us an opportunity to open the
burrow. The grasshopper was placed on its back, with its head next to
the blind end of the pocket and the legs protruding up into the tunnel.
We found that the egg of the wasp, which was seven millimeters long,
and rather slender, was placed on the under face of the thorax at a
right angle to its length, and parallel with the femur of the second
leg. This leg had apparently been stung so that it had swollen and
folded over the free end of the egg, which was thus firmly held in
place at both extremities.[3] Upon examination we found that the
abdomen of the grasshopper was beating regularly and automatically,
but the closest observation failed to discover any other movements,
nor would any part respond when stimulated. At three o’clock in the
afternoon we found the abdomen still pulsating, and, in addition, that
both antennæ moved several times when we lifted off the cover of the
jar that contained the insect. On the next morning the grasshopper was
very lively, the antennæ and labial palpi moving without stimulation.
It had passed fæces, and was able to lift its abdomen, which was
curved over toward the head, as it lay on its back, frequently and
with considerable violence. On the next afternoon there was no change
in the movements, but the egg was dead. On the seventh the grasshopper
responded to stimulation by a slight movement of the palpi and the
end of the abdomen. The pulsation of the abdomen continued until the
afternoon of the eighth, when it ceased, no effort of ours succeeding
in starting it again. The movements of the antennæ and palpi grew
weaker and weaker on the ninth, and on the morning of the tenth the
insect was dead, a period of five and a half days having elapsed since
it was brought into the nest.
We had not supposed that the digging up of her nest would much disturb
our Sphex, since her connection with it was so nearly at an end; but
in this we were mistaken. When we returned to the garden about half an
hour after we had done the deed, we heard her loud and anxious humming
from a distance. She was searching far and near for her treasure
house, returning every few minutes to the right spot, although the
upturned earth had entirely changed its appearance. She seemed unable
to believe her eyes, and her persistent refusal to accept the fact
that her nest had been destroyed was pathetic. She lingered about the
garden all through the day, and made so many visits to us, getting
under our umbrellas and thrusting her tremendous personality into our
very faces, that we wondered if she were trying to question us as to
the whereabouts of her property. Later we learned that we had wronged
her more deeply than we knew. Had we not interfered she would have
excavated several cells to the side of the main tunnel, storing a
grasshopper in each. Who knows but perhaps our Golden Digger, standing
among the ruins of her home, or peering under our umbrella, said to
herself: “Men are poor things: I don’t know why the world thinks so
much of them.”
[Illustration: NEST OF SPHEX]
Dr. Packard describes Sphex ichneumonea as nesting in gravelly walks,
where it digs to a depth of from four to six inches, using its jaws
and fore legs to do the excavating. While the wasps that he observed
completed the hole in half an hour, ours was actually at work a little
over four hours. Her nest, as is shown in the drawing, measured
seven and one half inches to the beginning of the pocket, which was
three quarters of an inch wide by one and one half inches long. The
yellow–winged Sphex, a native of France, was found by Fabre to take
several hours to make her nest, working in hard ground; while another
species, also studied by this observer, dug in soft earth, either in
the ground or in the accumulations on the roofs of buildings, and
completed her work in fifteen minutes at the most. These variations in
the habits of closely related species should be carefully studied in
any attempt toward an explanation of their instincts.
Fabre’s account of the genus Sphex, as it appears in France, is
most interesting. He says that the yellow–winged species, living in
colonies, first digs her nest and then secures her cricket, which is
brought, on the wing, to the neighborhood of the burrow, the last part
of the journey being accomplished on foot. The cricket is dragged by
one of the antennæ, and is not left until the nest is reached. It is
then placed so that the antennæ reach precisely to the opening, and
there it is left while the wasp descends hurriedly into the depths of
the burrow. In a few seconds she reappears, showing her head outside,
seizes the antennæ of the cricket, and drags it below. These manœuvres
are repeated with a striking degree of invariability.
The other Sphex first secures her prey, which is too large and heavy
to be carried far, and then digs her nest in the neighborhood of the
capture. This being done, she returns to her victim, and straddling it
drags it by one or both of the antennæ. Sometimes the whole journey is
accomplished at once, but oftener the wasp suddenly drops her burden
and runs rapidly to her nest. Perhaps it seems to her that the entrance
is not large enough to accommodate a creature of such size; perhaps she
imagines some imperfections of detail which would impede the process
of storing it up. The work is retouched, the doorway enlarged, the
threshold smoothed. Then she returns to her booty and again starts
with it. After a few steps the Sphex seems to be seized with another
idea. She has visited the doorway, but has not seen the interior. Who
knows whether all is well within? She drops her prey and again runs
off. The visit to the interior is made, more touches are given, and
once more she returns. Will the journey be accomplished this time?
Impossible to say. Some wasps, more given to worry than others or more
forgetful of the small details of architecture, to repair their neglect
or to clear up their suspicions, abandon their booty five or six times
in succession to retouch the nest or simply to visit the interior. The
prey, once brought to the nest, is carried in without the preliminaries
that are common to the other species.