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.

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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.

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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 coeruleum 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.

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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 Coeruleum 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, coeruleum 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.

Coeruleum 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.