THE ENEMIES OF THE GRASSHOPPER
EARLY in September a little black Tachytes suddenly became very common
in the garden. The first one that we saw was going forwards in a series
of long jumps, carrying a small grasshopper which was held by the base
of the antennæ. She soon doubled on her tracks, and it became evident
that she did not know her way; but after going about in circles for
two minutes she ran into her nest. When she came out she spent a long
time in circling around, flying close to the ground in wavy, snaky
lines, occasionally alighting to run a few steps; but in spite of this
locality study, ten minutes later, when she came jumping along with her
second grasshopper, she had lost her nest again and hunted about just
as before, twice going directly over it without seeing it. While she
was thus occupied another wasp of the same species attacked her and
tried to get possession of the grasshopper, but the rightful owner was
able to defend it. At last it was stored away, and she proceeded to
fill the nest, scratching the earth in with her first legs and working
it down with the tip of the abdomen. She worked quietly but steadily
for ten minutes, closing the place neatly, and then brought bits of
leaf and pieces of earth to cover it all over.
[Illustration: TACHYTES]
On the same afternoon we saw another of these wasps digging her nest,
but she was so much disturbed when we came anywhere near her that we
were obliged to retire. On the next day we saw her astride of a small
grasshopper, jumping along like the one of the day before. She too had
great trouble in finding her way. When she reached the nest she laid
her prey down while she went inside for a moment, and then, coming
out, seized it by the antennæ and backed in with it, instead of taking
it in forwards as was done in the other case.
Another wasp of this species carried a much larger grasshopper, which
was so heavy that she could not jump with it, but was obliged to keep
to the ground. In this case only one was used instead of two, which is
the usual number. This wasp was first seen at a distance of twenty feet
from her nest, and yet she went straight to the right spot without the
least confusion, showing that some individuals of the species have a
better idea of locality than others.
The nest is a short, shallow tunnel with an enlargement at the end,
within which are placed the grasshoppers, on their backs, with their
heads in. Earth is packed solidly into the tunnel, but not into the
cavity at the end.
We took two eggs of this species. Each was placed across the thorax
of the grasshopper at the base of the neck, on the ventral side. Both
hatched at the end of thirty–six hours from the time they were laid,
ate for three days, and then spun their cocoons. One of them ate only
one small grasshopper, leaving a second one untouched, while the other
finished the large grasshopper that formed her sole provision.
The grasshoppers taken from the nests, five in number, were in all
cases alive, there being a quivering of the mouth parts, and in some
cases of the legs also, without any stimulation. This condition lasted
for twenty–four hours from the time the poison was injected. After that
they became quiet, but remained alive until they were destroyed by the
larvæ.
[Illustration: NEST OF TACHYTES]
It is a curious thing that in these wasps is found the perfection of
that method of paralyzing the prey which is so much dwelt upon by
Fabre, although from their habits this fine workmanship is not of the
slightest use to them. They entomb their victims underground, where the
conditions are favorable to their preservation, and the extremely short
period that elapses between the laying of the egg and the spinning of
the cocoon makes it a matter of indifference whether the grasshopper is
alive or dead, since in any case it would be eaten before decomposition
set in.
We deserve no credit for discovering a second species, Tachytes
peptonica, for by her loud buzzing, slow flight, and persistent
hovering over the nest she gave us every assistance in her power.
She looks and acts like one of the large leaf–cutting bees, and this
resemblance is heightened by the fact that the grasshopper which
she carries is frequently of a leaf–green color. Her nest, which
is sometimes on the bare ground and sometimes in the grass, has no
external sign to mark it, and when with a great deal of fuss and
buzzing she descends and burrows, it closes behind her and disappears
from view, so that unless one marks the exact spot there is no way of
detecting it afterward. On her exit a very slight amount of scratching
closes the hole and leaves it looking exactly like the surrounding
surface; so that in comparing her work with the protracted labor of
Ammophila and some species of Pompilus in disguising the locality of
the nest, we were struck by the success to which she attained with a
very trifling amount of effort.
It takes peptonica thirty or forty minutes to catch a grasshopper, and
at each visit she remains for ten or fifteen minutes inside the nest.
The grasshopper is carried in the mandibles, supported by the second
and third pairs of legs. We never succeeded in opening a nest of this
species, but a grasshopper taken as the wasp was bringing it home did
not die until the sixth day.
In our summer work we often found ourselves wishing that we could
be in half a dozen places at once and could chase several wasps at
the same time. Never did we feel these desires more keenly than on
the twenty–ninth of July, when, after spending the best part of an
hour in watching the hunting of an Ammophila, we were obliged to
choose between following her to a possible conclusion, and giving our
attention to a little jet–black wasp, Lyroda subita, which we now saw
for the first time. This wasp was running around a bunch of clover in
a nervous, agitated manner, as though she were oppressed by some great
anxiety. The chance of discovering something entirely new decided us to
relinquish our Ammophiline hopes, and we sat down at the feet of our
new teacher.
We could not see anything remarkable about that bunch of clover, but
certainly the spot had some strong attraction for the uneasy little
wasp. She ran off first in one direction and then in another. She
circled about and made short flights now this way and now that, but
always returned. At last she betrayed the secret of her interest by
descending to the ground and picking up a small black cricket which had
been lying close by all the time. She flew up into the air with it, but
even now did not leave the neighborhood, continuing to fly about from
place to place, alighting now and again on the bean plants.
After this performance had lasted for five minutes she brought her
burden back to the same spot that it had occupied before, laid it down,
and without vouchsafing to us any explanation of her conduct, began
to burrow into the soft earth. She went down head first, backing out
with the dirt, which she carried with the front legs. While she was
thus occupied we defended her booty against two hunting parties of
ants which, at different times, fell upon it and would certainly have
carried it off if we had not been at hand.
It took the wasp twenty minutes to open the burrow, although, as we
afterward learned, it had been excavated before. At the end of that
time she turned around inside, came out head first, and dragged the
cricket within.
We at once opened the nest, but found it impossible to follow the
tunnel on account of the crumbling of the earth. Indeed, we almost
concluded that we were doomed to complete failure, for it was not
until we had gone down between six and seven inches that we found, in
a little pocket, our wasp in company with three crickets, upon one of
which was a larva a day or two old. At the time we knew nothing of the
habits of Bembex spinolæ, and we were much astonished to find a wasp
which evidently fed her young from day to day.
The contents of the nest were carefully conveyed to our wasp–nursery
at the cottage. The cricket that we had seen taken in was dead, as was
also the one upon which the larva was feeding. The third one was alive,
as was shown by a rhythmic movement of the palp on the right side. By
the next day, however, this one also was dead.
On the morning of the third day, July thirty–first, the larva had eaten
all of the first cricket and the greater part of one of the others,
leaving only the large hind legs. Supplying the place of the mother,
we killed two more and put them into the tube. One of these was eight
millimeters long, this being about the size of those which the wasp
herself had caught, while the other was of another species and much
larger, being thirty millimeters long. Its size and kind, however, made
no difference to the larva, which attacked this one next, although
there were two small ones yet untouched. It ate only half of this
big one, however, and then passed on. On August second we gave it two
more small crickets, and for that day and the one following its good
appetite continued, but on August fourth it stopped eating. We thought
that its larval life must be completed, and expected to see it spin its
cocoon, but something was lacking which we were too ignorant to supply,
and on August fifth it died. It had eaten six small crickets and half
of the large one, which was equal to about two more. Thus ended our
only acquaintance with this interesting little wasp.
The second week of August furnished such good play in our garden that
island life was neglected; but one brilliant morning we rowed over to
the home of Bembex and Philanthus, hoping that something new was in
store for us. We were not disappointed, for as we climbed the crest we
met a splendid Chlorion cœruleum dressed in shining blue, cricket in
mouth, plunging down the hillside through the long grass. Twenty–five
feet below, she reached her underground home, vanished for two or
three minutes, and then, coming to the entrance, turned her head from
side to side as though listening. Some indiscreet insect was chirping
loudly not far away, and before long the wasp ran out into the grass,
flew to a stump, dropped to the ground, flew to the top of a tall
weed, dropped again, and ran into a hole. A moment later she came out,
dragging a very limp cricket. An ant that crossed her path was chased
vindictively, and then the cricket was placed on its back and scraped
from head to foot four or five times with the mandibles. She then ran a
little farther, laid it down again, and repeated the operation, after
which it was taken into the nest.
[Illustration: CHLORION AND THE INDISCREET CRICKET]
To find ourselves on the track of a lively wasp at the beginning of her
day’s work was great good luck, and as Madam Cœruleum was perfectly
fearless and did her hunting on foot, instead of disconcerting us with
the long flights by which many of our wasps made the chase hopeless, we
had every chance to learn her ways.
It was a fatal day for the crickets. Between nine o’clock and one,
sixteen had been packed away, enough to provision three cells, as we
knew from former observations. Her manner was brisk and energetic, as
she ran about poking her head into every likely hole. At one time we
saw her dislodge a cricket which tried to escape by hiding under some
brush. She pursued, there was a lively scrimmage, and it was pulled
out quite limp and was then held in the mandibles, back up, while she
gave it a prolonged sting under the neck, after which it was carried
home without further manipulation. At another time she paused in
her homecoming to give the victim one long squeeze at the neck. The
crickets were placed in pockets, neatly arranged on their backs with
their heads inward and their long legs projecting into the main tunnel.
They were alive when taken, but died from day to day in the laboratory,
the larvæ eating them in this state without criticism.
While we were watching we noticed a much smaller wasp hovering about,
and presently she slipped into the nest. When the owner returned and
found her, there was a slight commotion in the passage–way, and then
the inquiline appeared, shaking her wings in a flippant manner, as
though she cared nothing for an encounter with the Big Blue. Instead of
coming out immediately as usual, cœruleum stayed inside for twenty–five
minutes. We should like to think that she was occupied in finding and
destroying the egg of the parasite, but we have no reason to suppose
that she could recognize that menace to her fortunes.
Cœruleum lives in her nest and enlarges it from day to day to fit her
necessities. On going over to the island one morning we found a cricket
sleeping calmly in the entrance way, little guessing how dangerous
was its position. It did not budge until the wasp came creeping up
from below, when it jumped away to a place of safety. Before the day’s
hunting began, a long study of the locality was made on foot, tufts of
grass, weeds and stones being carefully noted, and this accounts for
the ease with which the nest is afterward found.
One July afternoon we saw a little red Tachysphex tarsata on the Bembex
field of the island. She had a very anxious air, and was running
about wildly and rapidly, holding a small grasshopper with the third
pair of legs. She let it drop four or five times, and when she picked
it up again she seemed to sting it, but of this we were not quite
certain. At last she left it and began to rush about, investigating
the Bembex holes, entering one of them and perhaps throwing out a
little dirt as though she intended to use it, and then hurrying off
to another. We have no doubt that her confusion was the result of her
having lost track of a hole that she had made, as was the case with P.
quinquenotatus in one of our earlier observations. The Pompilus, after
a long search, resigned herself to the necessities of the case and made
a new nest; but this little wasp could not adjust herself to a break
in the system of her instinctive activities, and at last deserted her
prey and disappeared. We waited for an hour; and then, as she did not
return, we took possession of the grasshopper. It gave no response to
stimulation and never revived, a very careful examination later showing
that it was quite dead.
On the next morning we again saw this wasp on the Bembex field. She was
looking for a nesting–place, and when she had selected one she began
to work; the weather was warm and sunny, so that the Bembecids were in
the full swing of their obstreperous activity, and perhaps resenting
the presence of the little red wasp, or perhaps in a spirit of teasing,
they kept snatching her up and carrying her off to a distance of two
or three feet. She took these interruptions with the most philosophic
composure, hurrying back to her work as soon as she was released,
without any display of resentment. When the nest was finished, she
made a careful locality study both on foot and on the wing and then
flew away. In twenty minutes she came back, apparently to refresh
her memory, for she again made careful notes of all the points that
could help her to identify the place. She dug a little more and then
departed, to return five minutes later, on foot, with a grasshopper.
In spite of all the precautions she had taken, at this exciting moment
she was unable to remember just where her nest was, and spent some time
in running wildly about, but when she did find it she went in without
delay. We caught her as she came out, and dug up the grasshopper,
but found no egg, so that she probably would have brought in a second
victim had we let her go. The tunnel ran in obliquely for an inch and a
half, the pocket at the end being two inches below the surface.
A few days later we saw Larra quebecensis, another little grasshopper
wasp, with the same red abdomen as tarsata, going to and fro about her
nest, occasionally throwing out a little sand. She ran about near by
all through the afternoon, but was not in a mood for work. On the next
morning at ten o’clock, we found her touching up the nest a little,
after which she left it open and flew away. In an hour she came leaping
along like Tachytes, holding a small grasshopper in the third legs.
This was placed inside the door while she turned around, and was then
pulled in. She came out immediately, and in twenty minutes brought a
second, and in ten more a third grasshopper, staying within this time
for some minutes, after which she closed the nest. We took out the
grasshoppers, one of which bore an egg underneath, in the middle, in
front of the first pair of legs. The grasshoppers lived for five, six,
and seven days, but the egg did not develop. We once saw a quebecensis
that had laid down her grasshopper while she hunted for her nest. She
was moving in sinuous lines up and down the face of a cliff, with
incredible rapidity; we could not distinguish her, but could see only
a black streak with an occasional flash of crimson. When she rises on
her wings, too, she is wonderfully quick, disappearing as if by magic,
it being quite impossible to even guess at the direction she is taking.