SEVERAL LITTLE WASPS

IN a search for the nest of one of our garden wasps we found, in the woods beyond the fence, an old, weather-beaten stump which was riddled with holes both large and small. The large ones were evidently the passage-ways of ants, and were in constant use. The small ones seemed to be uninhabited; but thinking they might contain the nests we were in search of, and hoping that if we watched long enough we might see our wasps flitting in and out, we settled ourselves close by. We were resolved to stay as long as was necessary, and we blessed the fate that made it our duty to sit on the grass under the shade of a wide-spreading oak rather than in the distressing glare and heat of the garden; for this was on the tenth of July, and the weather was what the farmers call “seasonable.”

Twenty, thirty, forty minutes passed. Our eyes ached with persistent gazing, and we had nearly made up our minds that the likely-looking little holes were untenanted, when lo! a tiny wasp, carrying something which we could not see distinctly, darted into one of them. It was gone so quickly that we could not be sure that it was the species we were looking for, and when it reappeared, after two or three minutes, we saw that it was not. This point being determined, we watched the hole with redoubled interest.

It was wearisome work, for the wasp stayed away a long time, and we dared not let our gaze wander lest she should slip in without our knowledge. At the end of thirty-five minutes she returned, but again we failed to see what she carried. She flew with great rapidity, and we scarcely caught sight of her before she vanished into her nest. We could not but wonder at the ease and certainty with which she recognized her own doorway among the hundreds of holes on the side of the stump. This power of localization, while it is one of the most common among wasps, is surely also one of the most remarkable.

Our little Rhopalum pedicellatum, for that proved to be her name, made six more journeys within the next two hours. At the end of this time we opened the tunnel, and, after a great deal of sawing and cutting, succeeded in finding the nest five inches from the surface. It was nothing but a slight enlargement of the gallery, in the soft decaying wood. In it we found thirty-three gray gnats, all of them, except two, being dead. On one of the dead ones was the egg, which had probably been laid within a few hours.

The egg hatched two days later, on July twelfth, but on the fifteenth the larva died. By this time many of the gnats looked very dry, although we had tried to arrange for both moisture and ventilation by packing the bottom of the tube with pith and covering the top with muslin.

Further watching gave us one more wasp of this species, in the same stump. This time the nest was only two inches from the surface. It contained four dead gnats and two live ones, but no egg, showing that the egg is not always laid on the first ones stored.

Much later in the season, toward the end of August, we found another species of Rhopalum which proved to be new, and for which Mr. Ashmead has proposed the name rubrocinctum, since it wears a red girdle around the front end of the abdomen, being otherwise dressed in black like pedicillatum. It makes its home in the stalks of raspberry bushes. We opened a stem which contained thirteen compartments, separated by partitions of pith. These were filled with black, gray, and green gnats, which were packed in so closely that they were doubled over and pressed out of shape. Each cell contained from twenty-five to thirty gnats. In some of them were cocoons, in others larvÆ, and in one was an egg. The gnats were very carefully examined, and all of them, from the cells that had been filled last as well as from those provisioned earlier, were dead.

Other species of Rhopalum are said to prey upon spiders and aphides.

In studying the species that come in our way we are continually developing distinct likings for some kinds above others. The appearance of one of these favorites is always hailed with delight, and when the season’s work is over we remember them with lively pleasure. ill75

It is thus, dear little Oxybelus, that we dwell upon the thought of you and your pretty ways. No other wasp rose so early in the morning, no other was so quick and tidy about her work, so apt and business-like without any fuss or flurry. No other was more rapid and vigorous in pursuit of her prey, and we think with admiration and gratitude of the number of flies that you must have destroyed in the course of the summer.

O. quadrinotatus is only one-quarter of an inch long, and is dark gray with four whitish spots on the abdomen. It was before nine o’clock in the morning that, while out on an early inspection tour in the garden, we saw one of these wasps descend upon a sandy spot, and after a moment’s rapid scratching with her first legs enter the hole that she had opened. Under her body she was carrying a fly which looked like the common domestic species. It was upside down, its head being tightly clasped with the third pair of legs, and all of its abdomen projected beyond the abdomen of the wasp. Ashmead quotes from Fabre the remarkable statement that Oxybelus carries her flies home impaled on her sting, an idea that probably arose from the fact that nearly the whole body of the fly is visible.

Our new-found wasp stayed only a moment in her nest, although, as we afterward found, it was long enough for her to lay her egg on the fly. When she came out she quickly smoothed the sand over the spot with her head and legs so that there was nothing to mark the nest, and flew away. In three minutes she returned with another fly. She alighted two or three inches away, and scratched for an instant, but quickly saw her mistake, and found the right spot.

Again and again the pretty little worker went and came, while we sat watching close by, admiring her deft handiwork in opening and closing the nest and wondering at the ease with which she found it at each return. There was nothing tiresome or dilatory about this species, and within twenty minutes we had seen six flies stored up. The nest was closed and the place smoothed over every time before she went away, but when she entered she left the door open behind her. We once tried to make her drop the fly, but when disturbed she flew up and alighted on a plant near by, keeping her hold on it. The whole performance was brisk and business-like, but without the feverish hurry of Ammophila and Pompilus.

After the sixth fly was taken in we were afraid to let her go again, thinking that the nest must now be completely provisioned, and that she would not return. She was such a charming little wasp, scarcely bigger than a fly herself and yet so useful in her industry, that we hated to disturb her; but as we were obliged to have her for identification we first caught her, and then opened the nest. It contained only the flies that we had seen taken in, the egg being attached to the one lowest down, on the left side, between the head and the thorax. It was long and cylindrical. The flies were dead, but showed no marks of violence. We learned later that it takes Oxybelus two hours to make her nest so that this one must have been prepared the day before.

The egg, which was laid just before nine o’clock on the morning of August seventh, hatched at a little after nine on the morning of August eighth. The larva began to eat at once, and devoured all the inside of the thorax and abdomen of the fly to which it was attached, in the first twenty-four hours. On August twelfth it had reached the sixth fly, and we supplied it with three more. On August fourteenth these were gone, and we again replenished its larder, this time with two flies. The larva had partly eaten these when something went wrong. Its appetite failed, and on August sixteenth it died.

On further acquaintance this wasp lost none of her charm,—indeed, she gained in interest from the almost human curiosity that she showed about the affairs of other people. Where several were living close together one of them would sometimes stop digging her own nest to perch on a weed and watch the labor of another, and we once saw an especially inquisitive character burrow through the closed door and enter the home of her next-door neighbor.

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We find but meagre notes on the genus Oxybelus. Ashmead says that no observations have been made on the American species, but that in Europe they are found to burrow in sand and to provision their nests with dipterous insects. He says also that according to Verhoeff the species in this genus do not paralyze their prey by stinging, as they are unable to do so on account of the rigidity of the abdomen, but that instead they crush the thorax with the mandibles just beneath the wings, the centre of the nervous ganglia. He found in one nest a dozen flies, and all had the thorax crushed and were dead. In the case of our wasp we do not know how the flies were killed, but there was no crushing of the thorax. The larva devoured, in all, ten flies. At the time of its death it had probably finished the larval stage of its existence, since nine days had elapsed since the hatching of the egg. It may be that this period just before pupation is a critical point in the life history of a wasp, for we lost several of our nurslings at this time, and Fabre has noted that when, on account of the presence of parasites, the larva of Bembex rostrata had lacked something of its usual amount of nourishment, it perished miserably at the end of its larval stage, not having strength enough to spin its cocoon. No waspling in our charge ever died from lack of nourishment—on that score our consciences are clear; but it was difficult to make their conditions quite normal, and for this reason we may have been, indirectly, the cause of their death.

The way in which our Oxybelus carries its prey is peculiar to itself. Bembex and Philanthus also hold their prey under the body, but use the second pair of legs, so that it does not project behind except at the moment of entrance into the nest. Quadrinotatus, as we could distinctly see, since she passed close to us several times in quick succession, clasps the head of her victim in the third pair of legs, and flying thus, with its whole body sticking out behind her, she certainly presents a very remarkable appearance.ill81

Aporus fasciatus is a dark gray species, and is less than half an inch in length. We were working one hot day in the melon field, when we saw one of these little wasps going backward and dragging a female of MÆvia vittata which was much larger than she was herself. She twice left it on the ground while she circled about for a moment, but soon carried it up on to one of the large melon leaves, and left it there while she made a long and careful study of the locality, skimming close to the ground in and out among the vines; at length she went under a leaf that lay close to the ground and began to dig. After her head was well down in the ground we broke off the leaf that we might see her method of work. She went on for ten minutes without noticing the change, and then, without any circling, flew off to visit her spider. When she tried to return to her hole it was evident that some landmark was missing. Again and again she zigzagged from the spider to the nesting-place, going by a regular path among the vines from leaf to leaf and from blossom to blossom, but when she reached the spot she did not recognize it. At last we laid the leaf back in its place over the opening, when she at once went in and resumed her work, keeping at it steadily for ten minutes longer. At this point she suddenly reversed her operations and began to fill the hole that she had made, kicking in the earth until the entrance was hidden. She then glanced at the spider, selected a new place, and began to dig again. Surprisingly large pellets of earth were carried out, backward, and loose dirt was kicked under the body by the first legs. At the end of two or three minutes she paused and remained perfectly still for a time, considering the situation. Her conclusion was adverse to the locality, for she soon filled in the hole, looked once more at the spider, and started a third nest in a new place. This in turn was soon abandoned, as was also a fourth. The fifth beginning was made under a leaf that lay close to the ground, so that we could not see her at all. Fasciatus! had we had the naming of her she should have gone down the ages as exasperans! We had now watched her for an hour in the intense heat; the bell for the noonday meal had sounded, hunger and thirst had descended upon us, and most devoutly did we hope that she was suited at last, but no—after twenty minutes’ work this place also was abandoned, and a sixth nest started. This, however, was the final choice, and after forty-five minutes spent in digging, it was completed. As the spider was brought toward the nest it was left again and again while the nervous little wasp flew to the hole, went in, examined, and came out again. At last she backed in, caught the spider by the abdomen, and dragged it down. It was too big—the head stuck in the hole; but she pulled from below while we pushed gently from above, and it slowly disappeared. When she came out we opened the nest and took the spider. The egg was fastened to the middle of the left side of the abdomen. This one, as was also the case with a second and third afterward taken from fasciatus, was much less affected by the poison than is usual among the victims of solitary wasps, moving from the time it was taken, without any stimulation, and improving rapidly from day to day. Our second spider appeared to be blind, and died upon the sixteenth day, while the third had entirely recovered by the seventeenth day after it was stung, and was released. Fasciatus, then, probably depends upon packing her victim in tightly to keep it quiet.

It was three days and a half before the egg that we had taken hatched. The larva developed rapidly, retaining its hold at the spot to which the mother had fastened it. The spider remained alive for six days, and the larva continued to grow for two days longer, when it died also, being at the time about two thirds grown. We had great trouble in protecting our growing larvÆ from the inroads of fungi, and this was one of the many that perished from that cause.

The next example of fasciatus that came under our notice was a remarkable contrast to the one that we have just described, being as slow and dignified as the other was nervous and hurried. She chose a place and kept to it, her steady labor being interrupted only by occasional visits to the spider; but it took her fifty minutes to complete the nest. When finished it was a small gallery running down obliquely for an inch and a half into the ground.

The only habit that this species can claim as peculiar to itself is the strange and useless one of filling up the partly made nests that it is about to abandon. We have never seen the sense of order carried to so high a point in any other wasp.

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On a hillside near our cottage stands a log cabin, deserted and untenanted save for small creatures of the wild, which, though a favorite spot with wood-boring wasps, is an unprofitable place for study because of the difficulty of cutting out their nests without destroying property. One day in early July, however, when we were in the full fervor of hunting and longed to utilize every moment, the wasps in our garden seemed to have resolved that enjoyment and enjoyment only was their destined end and way, and became so exasperatingly idle that in disgust we turned to the cabin. For half an hour we saw nothing more exciting than a Trypoxylon immuring her victims and a Pompilus hunting spiders under the eaves, but at the end of that time Passolocus annulatus, a tiny wasp new to us, came flying quietly along and entered one of the holes with which the ends of the logs were riddled. She was carrying an aphis in her mandibles, and when this was duly stored she reappeared and flew away. She had probably just renewed her work after a spell of rest, since from this time on for nearly an hour she came back regularly every four or five minutes. She nearly always alighted on a blade of grass before going into the nest, but did not appear to be malaxing her prey. Presently another stage in the game was reached. She no longer brought aphides, but little pellets of mud with which she plastered up the opening. After she had finished this task and departed, we carefully chiseled into the log and laid bare the nest. The tunnel ran in for about three inches, and ended in three pockets which were well stocked with dead aphides, there being fifty-seven in all. The innermost cell contained a larva, and in the others were eggs, one of which hatched on the next day and one on the day following. This second one was probably laid just before the nest was sealed, giving forty hours for the egg stage; and it proved to be the healthiest of the three. The others perished in early infancy; but this one passed twelve days in eating, not only its own share of provisions, but those destined for the other members of the family as well, and then spun its cocoon.

We afterwards saw many of these wasps working in the logs of the cabin, and noticed that they seemed to have seasons of leisure alternating with spells of active work, as though when one cell had been filled up and the egg laid they felt at liberty to amuse themselves for a time before beginning on another. When an entirely new residence was to be chosen they went house-hunting among the old holes in the logs; and whether they had a high standard of sanitary conditions, or whether they objected to making extensive repairs, a great many places were examined and rejected before they settled down. The choice once made, many loads of pith were carried out before the little householder was satisfied. After the new abode was put to rights, the wasp would pass a whole day in rest, spending much of the time in looking out of her doorway and perhaps in observing the doings of her neighbors, but when she began to work she was very industrious, and allowed nothing to interfere with her labors, paying no more attention to us, no matter how closely our curiosity led us to interrogate her, than if we had been trees blown about by the wind.ill89

Some of the wasps dig deep into the stems of bushes to form galleries for their nests, but we found one wise genus that went in only far enough to make one or two cells, thus saving the trouble of carrying her cuttings thirty or forty centimeters in direct opposition to the force of gravity. This was Odynerus, whose nests we found in July, in blackberry and raspberry stems. Our first species was perennis, whose nests bear her mark in the shape of a pellet of earth placed above each mud partition. One of her cells contained a wasp larva and about sixteen caterpillars, nearly one third of which were dead, while the rest were more or less lively. They seemed to have been stung near the anterior part, as the last three or four segments were jerked up violently when touched. The larva went on eating, and the caterpillars went on dying from hour to hour. At the end of the eighth day, the baby wasp finished its meal, having eaten all that had been provided for it, as well as two dead caterpillars from another nest.

Much interest attaches to the way in which Odynerus lays her egg, since instead of following the common fashion of fastening it to the prey she suspends it by a tiny filament of web from the wall or ceiling of her cell. Thus in O. reniformis, nesting in the ground, it is hung from the ceiling, a mass of very imperfectly paralyzed caterpillars being collected below, and when the larva comes out the thread lengthens until the tiny jaws reach the food supply. Startle it ever so slightly and the waspling retreats by way of its web, descending again only when everything is quiet. For twenty-four hours it retains this path to safety, and then, growing bold, it drops down and feeds at its ease.

We had opened hundreds of plant stems in quest of these suspended eggs without being so fortunate as to find one, and were therefore much pleased when our kind friend, Dr. Sigmund Graenicher, whose interest in bees keeps him in touch with out-of-door happenings, and who has given us much valuable help, brought us two stalks, one of which had in it a nest of O. conformis, while the other contained two freshly provisioned cells of O. anormis. In all three the egg had been hung from the side of the cell about one third of the way down, and in the nest of conformis, from which all but one of the caterpillars had fallen, it hung loose against the wall. In the other nests the lower part was packed tightly with sixteen small larvÆ, upon which lay the egg, supported in a horizontal position, although attached to the side wall exactly as in conformis, and above were eight more caterpillars, the whole forming a compact mass shut in by the usual partition of mud. So closely were they crammed in that after counting them we were unable to get them all back again, and although motionless in their narrow quarters they became quite active when relieved from pressure. This is an entirely different arrangement from that of O. reniformis, and since the larva is in contact with the caterpillars from the moment of hatching the manner of the egg-laying has no significance in relation to the safety of the young.ill91

Conformis hatched on the morning after we received it, sloughing off the skin of the egg, but remaining attached to it, and thus doubling the length of the thread by which it hung. The caterpillar was slightly separated from it, and it seemed to have no notion of feeling about for its food, eating nothing for twenty-four hours, but growing and developing nevertheless. We now piled up some caterpillars in contact with it, and it began to eat, but after its own caterpillar and as many as we dared take from anormis were gone it stubbornly refused to take soft, tender little spiders, or caterpillars out of our garden; and it perished, a victim to prejudice.

The two eggs of anormis were probably laid within a few hours of each other, since they had both hatched on the morning of the third day, and had broken from their attachment, beginning to eat at once. They cocooned on the fifth day after hatching.

We had long wished to find a nest of O. capra, and early in September fortune favored us. A neighbor of ours keeps a large tin horn hanging under the porch. One day when she wished to use it, no amount of blowing would bring forth a sound; and when she unscrewed the mouthpiece to investigate the matter, out tumbled several small green caterpillars and a quantity of dry mud. When we heard of this incident we begged that if it should be repeated the nest and its contents might be saved for us; and on the second of September we received the mouthpiece of the horn with a message to the effect that a wasp had been working at it for some days. Examination showed that there were three cells, each containing a larva and a supply of caterpillars, of which there were ten in the cell most lately formed, and only one left uneaten in the oldest. The caterpillars, all of them being alive, together with the wasp larvÆ, were transferred to a place in which they could be conveniently watched. None of the caterpillars died until they were attacked. The larvÆ ate all the food that was provided, the oldest one cocooning on the fourth, and the second one on the seventh of September. Of the third, we have no record, excepting that the caterpillars had all been eaten on September eighth.

We happened to be passing through our neighbor’s grounds at nine o’clock on the morning of September fifth, and calling to ask whether there had been any more visits from the wasp, we learned that capra had been seen making a mud partition in the horn on the day before. While we were speaking she arrived and entered the mouthpiece, where she remained for about ten minutes. When she departed we found that she had laid her egg, which we carried away with us, wishing to determine the length of the egg stage. This proved to be longer than that of any wasp that we had heretofore known, for not until the morning of September ninth did the larva make its appearance, the egg skin bursting and leaving its tenant free to crawl away. In other genera the egg changes into a larva imperceptibly, there being no sloughing off of the skin.

Capra, then, first finds a suitable crevice, and builds a partition across the inner end, the earth being scratched up from some dry, bare spot, and moistened in her mouth. Before gathering the ten or twelve small caterpillars that are to provision the cell, she lays her egg; and although we could not be sure, we thought that in this case as in the others it was suspended.

Unless the cell is tightly packed at the beginning, capra certainly needs the filament, for her caterpillars were so far from being reduced to a state of decent immobility that we had to press wads of cotton into the tubes in which they were kept to prevent them from wriggling out of the way of the larva. None of our larvÆ, not even the one-day-old ones, were injured by their activity; but had the egg been left to its fate among them it might have perished.

Later in September we found O. vagus bringing pellets from a sharp-edged hole in the ground. Her method was to carry each load on the wing to a distance of ten or twelve inches, where it was dropped without the lively fling with which Ammophila discards her lump of dirt. The red end of a match stuck into the ground two inches away proved very disquieting to the dainty little wasp. These colored matches were a great convenience in marking nests, and as we were using them constantly, we did not guess, for a time, what the trouble was. For half an hour she went and came, circling about, alighting upon plants, and seeming entirely absorbed in examining them with the minutest care, even alighting upon our hands with most engaging friendliness, but pretending all the time that the nest was naught to her. When the offending object was removed she hurried in at once and resumed her work. The storing was not begun until the next morning, when she took in six caterpillars of very different sizes, at intervals of from ten to twenty minutes, and then filled the hole. We hoped to find the little chamber arranged as in reniformis, but had not skill enough to excavate in such a way as to show the internal plan. It is remarkable that this genus, with only one set of tools for all its species, has worked out such different styles of architecture, the ground nests bearing no resemblance to those cut out of woody stalks; and its flexibility is shown in the use of empty snail shells by a foreign species, as well as by capra’s habit of partitioning off convenient crevices found ready made.

The prettiest nests that we have seen in stems are those of Plenoculus peckhamii, which separates its cells, not by solid partitions, but by numerous granules of earth, which are used by the larvÆ for forming the case of the cocoon. One raspberry stalk that we opened had at the bottom six of these mud cocoons, and above these three larvÆ eating, each in its own compartment, the provision in this case consisting of immature bugs of the genus Pamera. Sometimes the stalk which is being filled by Plenoculus attracts the fancy of a bee or of another wasp, as is shown by the upper cells being filled by Osmia or Crabro, or sometimes Plenoculus builds above the bee cells. When a number of wasp eggs are placed in a plant stem, the last one laid is the first to hatch. The different habits of the Hymenoptera in this respect are very interesting. In the case of Ceratina dupla, the small carpenter bee, the egg first laid hatches first, those above following in regular order. The lower ones wait patiently in their cells until the one in the top cell has matured, and then they all come out at once. When two species occupy the same stalk, the lack of adjustment probably results in the destruction of those lower down, excepting in the case of the cuckoo flies, which have acquired the habit of gnawing their way out at the side of the stem.