CRABRO

THE highest point of the island is crowned by a great group of linden trees; and one day their perfume, carried by the wind far over field and wood, was calling everything that had wings to gather the richest of all the gifts that July can offer. We, too, were drawn to the spot, and found the great blossoming domes thrilling and vibrating with life. For miles around, the bees, wasps, and butterflies had gathered to the feast; and we seemed to touch the high-tide of the year in the scent of the flowers, the humming throng of happy creatures, and the vision of it all against the summer sky.

Below, in a great root that had pushed above ground, five little wasps, by name sexmaculatus, of the worthy but unimaginative genus Crabro, resisting the intoxication of the linden flowers, were sawing and cutting in the most humdrum and practical manner. One of them, presumably the earliest riser, was well down in the root, and came backing up once in a while, pushing a lot of wood dust out of the hole. This was spread out by means of legs and mandibles, and was then blown away by the fanning wings of the little worker, who circled about just above the ground until the last grain had disappeared. Here was another way of protecting the home. The fresh dust might attract the attention of some cuckoo-like insect who would lay her egg within; and therefore it was dispersed, just as Ammophila carried out her pellet and flung it to a distance, and Sphex spread evenly over the ground the mass of earth that she carried from her hole.

After this series of actions had been repeated several times the wasp flew away to hunt. We afterward found that she had finished the third in a set of cells leading from a main gallery. On her return we delayed her to see what she was carrying. She showed no fear, but alighted close by, and while she was trying to transfer to the third pair of legs the fly that she was clasping with the second pair, it escaped and flew gayly away. Flies are plenty, however, and she soon had another which she was permitted to store; and from that time she worked busily until we left her at noon. It took her from two to ten minutes to catch her fly, and at each return two or three minutes were spent in the nest. On opening her tunnel some days later, we found within not only flies, but long-bodied gnats, and all of them seemed to have been brought home uninjured. When the freshest cell was opened some flew away, others were walking about, and all were lively. The wasp egg was laid on the under side of the neck; and although we could not be certain of the exact time of laying we thought it hatched at the end of thirty-six hours. From ten to sixteen flies were provided for each larva.

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A month later we found Crabro lentus nesting in the ground. Her tunnel ran down obliquely for six and one half centimeters, and had an enlargement at the end. Two bugs and a fly were in the nest, when we opened it before the provision was completed. To find sexmaculatus taking both flies and gnats was surprising, so rigid are the family traditions of the wasps; still, she might feel that so long as she drew the line at Diptera she was all right. But to believe that one wasp, a Crabro, too, with all the marks of conservatism about her, would take such diverse things as bugs and flies, is almost too much to believe. It is true that Crabro wesmÆli is said to use both flies and bugs;[4] but some accident may have led to this supposition, and stronger evidence is needed to prove that there is variability in so deeply seated an instinct.

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The Crabro wasps all have pleasant ideas as to where they want to live, but interruptus excels in the choice of a dwelling place. We lately found ten or twelve of them in Milwaukee, nesting in an old log on the shore of Lake Michigan, and when they opened their doors in the morning they had before them the splendor of the great bay; but calm in the midst of the glory they never paused on the threshold, as Cerceris would have done, to take a look at the world before going to work. One morning the earliest riser in our little colony was beginning the day at half past nine. Of good size for a Crabro, with a square determined-looking head and very direct and business-like manners, she proceeded to cut out a new chamber for provisioning. These chambers are nothing more than enlargements of the long gallery, such as are made in stems by related species. At ten o’clock she departed on a hunting excursion among the bushes on the bank above us, and came back in eight minutes, carrying, much to our surprise, a white-winged moth, which was clasped under the body by the second and third pairs of legs, and was passed back to the third pair as she alighted before entering. A moth is an innovation, a delicacy new to the accepted idea of what a Crabro larder, accustomed to Diptera, should contain. A moment later she was off again, but this time did not succeed so quickly, coming back twice empty-handed for brief visits, and bringing in a load at the end of half an hour. It took six moths to provision the cell, and as the number neared completion her interest and energy seemed to wax greater, the hunting intervals shortening to five, and even to two minutes. We found afterwards that some of the moths were alive and some dead, and that she packed them lengthwise, one after another, into the closely fitting chamber. At a little before eleven o’clock the cell was filled, and the wasp retired from sight, closing the door behind her. We thought that she was resting, but presently the protrusion of wood dust showed that she was enlarging her house, and an hour later she came out and began to hunt again. By this time half a dozen were working. Before leaving for the first time in the morning each one made a thorough study of the place, and on returning they entered their own doors, which were standing open, without hesitation, the long white wings of the moths trailing behind them. Four species were represented in the nests that we opened.ill106

Many species of Crabro make their nests in the stems of plants, and among these is stirpicola, which is seen in numbers, through the middle of July, flying about in a leisurely way, though it is only toward the end of the month, or in the early days of August, that they settle down to the work of making their homes. On the afternoon of July twenty-seventh, after some very lively work in the heat of the day, we walked down to the berry garden at half past five o’clock, rather to rest ourselves than with the thought of undertaking anything new; but a wasp-hunter cannot afford to choose his own hours, and we thankfully accepted the sending of fortune when we came upon a stirpicola busy at work in digging out her nest. She had only begun to excavate, and had reached a length just equal to that of her own body. Her manners were an agreeable contrast to those of the wasps that we had been watching through the day. The feverish excitement of their ways seemed quite in keeping with the burning heat of noon, while Crabro’s slow and gentle movements harmonized perfectly with the long shadows of evening. To fully appreciate the difference between Pompilus or Ammophila and Crabro it is necessary to see them at work. The one is the embodiment of all that is restless, vying with the humming-birds in swiftness and energy, while the other is calm, quiet, and stately in all that she does.ill-107

Some ten feet away was a second stirpicola, and this one, to judge from the depth to which she had penetrated, must have been at work for about two hours. We watched them both, and saw them bring up load after load of pith. They bit out the pellets with their mandibles, and passed them back between the legs and under the body until a quantity had accumulated above the tip of the abdomen. They then walked backward up the stem, and thus pushed out the mass as they came to the top. Often they used the hind legs to assist in getting it out of the way, sometimes kicking it to a little distance. Once in every two or three trips they would come out far enough to expose part of the thorax. They appeared and disappeared with the regularity of a machine, never stopping to rest.

We remained with them until seven o’clock, when we placed a long bottle over each stem in such a way that while it did not interfere with the work of the wasp, it caught the chips of pith as they fell out. At the end of an hour we noted the amount of accumulation in the tube, and thus had a measure of their rate of work. The drawing gives an idea of the arrangement of the tube on the stem. When we left them they were still digging and delving.

At half past nine we took a lantern and went down to visit our charges. We expected to find them at rest, and asleep; but on the contrary they were working as busily as ever, and upon examining the measuring glasses we found that they had not paused since we left them. We measured the depth of the dÉbris in the bottles, and then emptied them.

At four o’clock on the next morning we went to the garden, and were much surprised to find that the two wasps had worked without intermission throughout the night. Indeed they seemed to have shortened a little the time that it took to make a round trip down the gallery and up to the opening again, since there was more pith in the bottles than we could have expected if they had worked at only their former rate. Neither the coolness of the air nor the darkness of the night had made the slightest difference to them. After watching them a few minutes, and marveling at their powers of endurance, we cleared out the tubes and returned to bed. At half past eight we found them still at work. Unlike us, they had taken no morning nap, but had gone on with their tunneling in their usual steady way.

From this time their ways diverged, and they must be described separately. At nine o’clock the one that we had first seen came up to the opening, walking head first, and flew off, remaining away seven minutes. When she returned she at once resumed her work, and kept at it without a pause until two in the afternoon. At this hour she went away, and we never saw her again. We suppose that she was killed, for it seems improbable that so faithful a creature could have deserted her half-finished home. Pompilus quinquenotatus often deserted a partly finished nest for some more enticing spot, and Sphex started several excavations before making a final choice; but we cannot believe that there was anything fickle about Crabro.

The second wasp came up head first to the entrance of her hole at two minutes after nine, as though she had been influenced, in some subtle way, by her neighbor’s example; but after looking about for a moment she went back. She repeated this observation several times, and finally, at twenty-five minutes after nine, came out and flew to a leaf near by. Then she circled around, alighting a number of times, and at last departed. Her stay was brief, for at just thirty-five minutes after nine she returned, and at once settled down to her work.

We now began to make notes as to the length of time that it took her to go down and bring back her load. We timed her again and again, and found that she was remarkably regular, each of her trips occupying from forty-five to fifty seconds.

All that day we kept her under strict surveillance, and never once did she suspend her operations either for rest or refreshment. Late in the afternoon, while we sat watching her as she appeared and disappeared with almost the regularity of clockwork, we found it difficult to realize that the patient little creature had been at work for more than twenty-four hours, with only one brief intermission. Without hurry or flurry she kept at her task, reminding us, in her business-like ways, of the social wasps of the genus Vespa. When we left her, at dusk, we attached the recording tube to the stem, and at ten o’clock in the evening we found that she had not stopped working. We emptied the glass, and left her.

At seven o’clock in the morning of July twenty-ninth we paid her a visit, and could scarcely believe the testimony of our senses when we saw that the record was one of unceasing toil through the long hours of the second night. We began to wonder if she would ever finish her task. Wonderful though she was, we had grown a little weary of our long session of watching. We had been glad that she worked through the first night; it was creditable to her and interesting to us, and we admired her even more for sticking to it through the second, but when it looked as though we might have to remain by her side through another long day, watching an endless series of loads as they were carried out, we confess that we thought she was rather overdoing it. Gradually, however, she slowed up her work, taking two or three minutes to make a journey down and up. At last, at just nine o’clock, her head appeared at the top of the stalk, and after a slight hesitation she flew away. The nest was completed.

We have studied wasps for a number of years, and we feel that we are on terms of more or less intimacy with many of the species, but never before have we known one to work after day was done. We have often gone out with a lantern at bedtime for a tour of inspection among our nests, and have always found the inhabitants quiet and presumably asleep. The social wasps are very industrious, but during the hot nights of July they are to be seen clustered together on the outside of their paper nests in deep repose; and although the Vespa wasps that nest in the ground sometimes come home late in the twilight, we have never seen them work after it was really dark. Polistes fusca may be said to share our cottage, so thickly does she hang her combs under the shelter of our porches, and from observations taken at all hours we know that she is quiet through the night. Sir John Lubbock, in “Ants, Bees, and Wasps,” speaks of the great industry of wasps. He has known them to work from early morning until dusk without any interval for rest or refreshment; but here was our little Crabro toiling from three in the afternoon of July twenty-seventh, through that night and the day and night following until nine o’clock on the morning of the twenty-ninth,—a period of forty-two consecutive hours with one intermission of ten minutes on the morning of the twenty-eighth. Surely she takes the palm for industry, not only from other wasps, but from the ant and the bee as well.ill113

The nest was completed, but the work of storing it remained to be done. The wasp flew away at nine o’clock, and ten minutes later came back with something, we knew not what, for she dropped into her hole so quickly that she was out of sight almost before we knew she was there. Two minutes later she came up, and was off again. This time she was gone twelve minutes, and when she returned we were again baffled in our effort to see what she was carrying. When she came out she alighted upon a leaf and attended to her toilet, cleaning both body and wings by rubbing them off with her hind legs, and from this time on she never started on a hunting expedition without paying this attention to her personal appearance. On her third trip she was gone twenty minutes, coming back with a small fly; and before we left her at ten o’clock, she had stored six more. When we came back at half past two in the afternoon she was working, and she kept up her goings and comings until four o’clock, when she suspended operations for the day. On the next morning we were called away, and know nothing of what she did, but on the following day, Thursday, we resumed our observations. She worked hard all the morning, but in the afternoon her trips were few, and were made at long intervals. On Friday she worked from eight to nine, when she departed, and never returned. We watched for her, at intervals, all through that day and the next, when we were forced to conclude that our faithful little worker had fallen a victim to some bird or beast. We did not disturb the nest until four days later, when we cut the stalk, and examined it.

We found that the tunnel was thirty-nine centimeters in length. This was a long distance for her to excavate, and, all things considered, her progress had been rapid. We have opened a number of stems that had been stored by this species, and all the excavations were from thirty to forty centimeters in length, the width of the gallery being about three and one half millimeters, while on each side there was from one to one and one half millimeters of pith that had not been cut away. Of course these points varied with the diameter of the stem and also with the size of the worker.

Our little stirpicola had stored one cell, had laid an egg, and had built a partition of pith across the stem as a floor to the second cell, before her untimely taking off. Had she lived, ten or twelve cells would have been stored, one above the other. The completed cell contained a larva and parts of eighteen flies of different sizes, four species being represented. The flies had all been attacked by the larva, the abdomens of some and the thoraces of others having been eaten. The larva continued to eat for two days, and then spun its cocoon. The flies found in this and in other nests of stirpicola were all dead. All the pupÆ that we kept wintered in the cocoon and came out in the spring.

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The females of Crabro, like those of other genera, seem to use their galleries as sleeping places, but the males stop at any convenient inn. We once entertained one of them for several nights in a hole in one of the posts of our cottage porch. Other males, as in Philanthus, spend time and care in digging a hole in the ground, to which they return night after night. In Agenia the female keeps one cell ahead of her needs, and tucks herself away in it very comfortably; but the PelopÆi, instead of making this use of their tubes, congregate in the evening where there are convenient crevices, and make as much fuss about getting settled as a lot of English sparrows. Mr. Banks has made a delightfully pretty as well as interesting observation on the sleeping habits of Ammophila. In a corner of his garden where the grass grew long, dozens of these wasps arrived every evening, and after a good many changes in position, fell sound asleep, clinging to the stems about one third of the way down. They registered at this hotel between seven and eight o’clock, and departed before five in the morning. We have seen a Pompilus take the greatest care in selecting a sheltered spot under some leaves, where she afterward hung herself up, and slept soundly until after eight the next day; and Mr. Brues has found companies of Priononyx atrata passing the night on the stems of sweet clover.