AN ISLAND SETTLEMENT

OUR children often made themselves useful by reporting finds in the shape of nests, and one day they returned from the island with a wonderful tale of great numbers of big wasps that were digging in the ground. “I don’t know what they are,” said the small boy, “but they act to me like the maddest kind of hornets.” With this attractive picture before us, we lost no time in going over to the spot, where we found a thriving colony of Bembex spinolÆ. On our approach they fell upon us, “desire of blood, and rage, and lust of fight” in their mien, and chased us to a distance, but without inflicting a single wound. This temperance was not due to gentleness of disposition, but to the fact that Bembex is not at all handy with her sting, her body being too large and clumsy to curve and give the lightning stab as other wasps do. With renewed courage we again approached them, more cautiously this time, and soon learned that if we preserved an extremely composed and dignified demeanor our presence on the field would be tolerated.

Bembex, like Philanthus, and some species of Sphex, lives in a sort of semi-social state, a number of individuals occupying the same space of ground, although each one has its separate nest. Bembex, however, differs from these genera and from almost all of the solitary wasps in her habit of feeding her young from day to day, or rather from hour to hour, as long as it remains in the larval state. This difference in her maternal cares as compared with those of other species results in a less numerous progeny. The larva, for a period of two weeks, demands constant attention from the mother, so that a second egg cannot be laid until the first-born has gone into its cocoon, unless, indeed, she feeds two larvÆ at once, which does not seem probable. The season of work is ten or twelve weeks, so that Wesenberg is probably correct in allowing only five or six young ones to each mother for the summer.

In watching our wasps we found that the new nests were usually made in the outskirts of the colony, which was thus continually extending its limits. Like many other species, Bembex has great difficulty in deciding just where to dig. Our Sphex made three beginnings before finally settling down. The only Ammophila that we watched from the beginning changed her place after working for ten minutes. P. quinquenotatus often tried half a dozen places before she was satisfied, and spinolÆ is quite as difficult to please.

When, at last, the right place is found, the labor of excavation is carried on vigorously. The mandibles are used for loosening the earth, and for lifting, but the greater part of the work is done with the first pair of legs, the tarsi of which are doubled up while the dirt is swept out with the brush of stiff spiny hairs on the second joint. This attitude gives them a very comical aspect, making them look as if they were sweeping with their elbows. They sometimes lie far over to one side while loosening the earth with their mandibles. While digging, the body is held high by the straightening of the third pair of legs, and the dirt comes out behind in a rapid stream, flying to a distance of three or four inches. Before long the wasp is lost to sight, but every few moments she comes backing out, pushing behind her the dirt that she has displaced below. In about fifteen minutes the nest is ready, and the wasp turns her attention to scattering all the dirt that has been thrown out, sweeping the ground clean so that no sign of her work remains. We have often speculated as to the meaning of the careful and conscientious performance of this part of her task. With the wasps that nest by themselves it is not easy to see what enemy they are providing against in hiding the entrance to the nest; but the precaution seems still less necessary—even absurd—in the Bembex field, where there is no possibility of concealing the colony, and where the nests are only an inch or two apart, so that an enemy might burrow anywhere with the certainty of finding one. Moreover, the only enemy that we could discover was the parasitic fly, which never attempts to enter when the hole is closed. However, unmoved by our opinion on the subject, spinolÆ spends five or six minutes of her precious time in making the neighborhood of her home quite tidy, and then she fills in the mouth of the nest with a little loose earth before going away to catch her fly.

Oxybelus, though she is limited in choice by her small size, can catch a fly in three or four minutes. Bembex is strong enough to take anything that she sees, and she has no preference for one species above another, yet she seldom finds one under twenty or twenty-five minutes. When she comes back nothing of the fly is visible unless it is unusually large, so closely is it held under her body by the second pair of legs. She alights, and scratches away the loose earth at the entrance of the nest with her first legs, and then, as she creeps within, she passes the fly along from the second to the third pair, so that the end of its body, projecting beyond the abdomen of the wasp, is visible for an instant before it is carried inside. Sometimes she drops the fly behind her, and then, turning around, pulls it in with her mandibles. In other cases, where a longer portion of the tunnel has been filled with earth, the fly is left lying on the ground while the wasp clears the way. This offers a favorable opportunity to parasites, especially as the fly is not placed with regard to its safety, but is dropped anywhere. The dirt that is kicked out sometimes covers it so that when the way is clear the careless proprietor must search it out and clean it off before she can store it away. In one instance, in which we had been opening a nest close by, the tunnel was entirely blocked by the loose earth which we had disturbed, and the wasp worked for ten minutes before she cleared a way to her nest. During part of this time she held the fly, but when she realized that it was going to be a long piece of work she laid it down near by. As the wasp enters she sometimes leaves the hole open behind her, but oftener fills it by pushing up earth from below. When she comes out again she throws in a little dirt, and then begins to circle about the place. She seems not quite easy about the nest, however, returning three or four times to scratch earth over the entrance, before finally taking her departure.

We opened a good many nests in the course of the summer, and found them all very much alike, much more so than is the case with other species. The entrance tunnel runs in obliquely for from three to five inches below the surface of the ground, and ends in a pocket.

We grow accustomed to marvels, and from our familiarity with other wasps we take as a matter of course the unerring accuracy with which Bembex swoops down upon the exact spot at which the entrance to her nest is hidden. And yet how strange a power it is! There is not the least sign to help her—not a stone, not a blade of grass is to be seen on the field. Our method of marking a nest which we wished to find again was to place tiny pebbles at exactly equal distances from it, one on either side, so that the middle point of the straight line between them gave us the desired spot; and the wasp doubtless uses the same method, only her landmarks are sometimes so infinitesimal that we do not recognize them.

Bouvier finds that when he cuts away the plants around the nest of B. labiatus, clearing a space of twenty-eight or thirty inches square, the wasp is much confused, flying about for a long time before she is able to find her home. He once placed a flat stone over the entrance. The wasp alighted upon it, and after scratching vainly for a while made her way in. The stone was left in this position for two days, during which time Bembex learned to regard it as a landmark, for upon its being removed to a distance of eight inches she still followed it upon returning with her fly, and insisted upon finding her nest near it.

ill125

An observation of Marchand points to the same conclusion. He says:—

A curious thing about these wasps, and one which shows how much common feeling they have, is that they work in waves, all starting off on their hunting expeditions within a few minutes of each other, and returning together after the chase. At one time all the residents seem to be present, digging their nests, carrying in their booty, dashing at each other, and chasing the parasites with a tremendous amount of humming and swooping about. Then suddenly they are all gone. Nothing remains but multitudes of flies, which keep up a giddy dance over the field, and for ten or fifteen minutes the place seems deserted. Then the wasps begin to return, several coming at a time, and as if by magic the whole scene awakens to life. More than half of the wasps bring nothing home with them, and these fall to robbing their more fortunate companions. Those that are carrying flies must pause a moment, burdened as they are, to scratch away the earth at the entrance to the nest. When unmolested they go in very quickly, but it is just at this point that the marauders fall upon them, displaying an amount of persistence and energy in their attacks that, were it properly directed, might easily enable them to secure flies for themselves.

We once saw a wasp that had been fortunate enough, or perhaps unfortunate enough, to catch an immense fly, the wings of which stood out on both sides very conspicuously. This made her an especial mark for her unprincipled relatives. Half a dozen of them chased her about, like chickens pursuing one of their number that has found a worm. She circled and settled, and circled and swooped around for five or six minutes, continually pursued and attacked by the robbers, and quite unable to get into her nest. At last, curious to see what she was carrying, we made her drop her load, and secured it for ourselves. We found it to be a horse fly, quite dead, but showing no marks of violence. It was not wasted, for we afterward fed it to one of our wasp nurslings at home.

At another time we saw one wasp attack another that was bringing in a fly. In the struggle that ensued the owner lost her booty, as the two rolled over and over on the ground, and as they parted it was seized by the thief. They clinched again, and rolled on the ground as before, and this time the fly was recovered by the rightful owner. At this point, thinking that perhaps one of the wasps was a male, and that this might be their style of courtship, we seized both of them; whereupon the fly was dropped, and the two wasps turned their attention to attacking us. Both proved to be females. Not only do the Bembecids fight in this way for the possession of their prey—they quarrel even without apparent cause. We have seen two females digging their nests at a little distance apart, one of which was repeatedly attacked by the other, although she did nothing to provoke the aggressor. They are certainly very unneighborly, and have no idea of living in harmony. When flying in a threatening manner, either at us or at each other, they have a way of wagging their abdomens violently from side to side in a way well calculated to inspire terror.

In warm sunny weather spinolÆ works industriously through the middle of the day, and seems determined to provide abundantly, not only for her own offspring, but for any unbidden guests that it may be her fate to care for. She never works more than four or five hours a day, however, and in unfavorable weather she does not work at all. On going over to the island one cloudy morning to spend some hours in watching the Bembex activities, we found the spot quiet and lifeless. No one seeing it for the first time would have dreamed of the multitudes of living creatures beneath his feet. The nests seemed to be all closed, but on peering curiously about we found one on sloping ground, in the suburbs of the colony, of which the door was open. Just within was the proprietor gazing out on the landscape, as she is shown in the illustration. She seemed to be leaning on her elbows, and her face, enlivened by two great goggle eyes, had an irresistibly comical aspect. With the exception of the omnipresent flies, this wasp was the only sign of life about the place. Even in good weather, and in working hours, the wasps sometimes rest, for we have seen them go in empty-handed, closing the door behind them, to remain for half an hour at a time.

ill131

There is one thought that must strike even a casual observer at the sight of the hordes of parasites that hover over a Bembex colony:—

“The buzzing flies, a persevering train,
Incessant swarm, and chased return again.”

Why do not these wasps, fly-catchers as they are by profession, kill the worthless wretches that infest their homes, thriving abundantly on the fruits of their labor, a continual menace to the life and safety of their offspring? To the uninitiated it would seem that these flies might serve as food for the wasp larvÆ quite as well as any of the dozen species that they actually take; but even if the wasp-mother believes that they possess indigestible qualities, it would be much less trouble to kill them and throw them away than to be perpetually chasing them to a little distance only to see them return as soon as she gives her attention to anything else. Whatever the reason for it may be, the relation between the wasps and the flies is certainly most curious and puzzling. Fabre’s explanation is that since this miserable little fly has its own part to play in nature, Bembex must respect it, thus preserving harmony in the world of living things. The idea is perfectly in accord with his own theories, but we find ourselves quite unable to accept it.

There can be no doubt that the parasites are a grave danger to Bembex. She suffers from them far more than any other wasp that we are familiar with, her mode of feeding the young rendering her peculiarly susceptible to their attacks. Of the ten or twelve nests that we opened only one was free from them, the others containing from two to five lively maggots nearly as large as the wasp larvÆ, which were sharing the food brought in by the mother. Fabre, who has studied the question thoroughly, has found as many as ten parasitic larvÆ in one nest. He has also noticed that where the parasites are most numerous the wasp-larva is proportionately small and emaciated, reaching only one half or one third of its normal size. When it attempts to spin its cocoon it has not strength enough to do so, and thus perishes miserably among the pupÆ of the interlopers, which have the advantage of developing more rapidly. He has proved, by experiments upon nests transported to his study, that although the invaders preserve friendly relations with the rightful owner of the nest so long as food is abundant, they nevertheless, at the first suggestion of scarcity, fall upon the wasp larva and ruthlessly devour it. This “black action” he has seen with his own eyes. In view of this base ingratitude, we are more than ever impressed with the troubles of the poor Bembex mother, as she tries to feed a dozen mouths where she has bargained for only one.

We several times saw a fly follow a wasp into her nest, remaining within for half a minute, and it is probable that they go in to lay their eggs. According to Fabre, it is the habit of the flies that are parasitic upon the half-dozen species of Bembex that he has studied to seize the moment at which the fly projects from under the abdomen of the wasp as she enters the nest; and he has even known them to lay two or three eggs on one fly in the instant of time that its body was exposed.

Fabre took a partly grown Bembex larva from the nest, where it was surrounded by the remains of twenty flies. He fed it generously, and it ate sixty-two more, making a total of eighty-two in the eight days that passed before the spinning of the cocoon. Our experiments in this line gave similar results. We took charge of a partly grown larva on the afternoon of August tenth, and between that date and August fifteenth, when it spun its cocoon, it ate forty-two house flies besides a big Tabanus.

Fabre thinks that under natural conditions the mother does not give the larva all it can eat at one time, but provides it with what she considers a reasonable amount of food, and keeps anything that she catches beyond this out of its reach. He draws his conclusion from the fact that he has found several flies in the tunnel leading to the nest, while the larva had as many more close to it. It would certainly be convenient for Bembex to have a reserve of this kind in case of rainy weather, but the forethought implied in such an action seems to require a higher degree of intelligence than can be claimed for her.

In one nest we found a single fly with a long cylindrical egg attached to the left side of the thorax just at the origin of the third leg. In another, which we had seen made and provisioned, we found, six days later, a larva which we judged to be four days old. Assuming that the egg was laid on the first day, it must have taken it about two days to hatch. Other nests gave us larvÆ in all stages of development, surrounded by the remains of Diptera, among which Syrphus, Tabanus, and Musca were represented.

In regard to the condition of the flies captured by Bembex, we have never seen the crushing of the thorax, which is noted by both Wesenberg and Fabre. Indeed, the flies that we found were not always dead, since in two instances they responded readily to stimulation. Similar results have been obtained by Mr. S. W. Dunning of Hartford, Connecticut.

Twice we have seen our spinolÆ, as she was bringing home her prey, alight near the nest and sting it as it was held with the second pair of legs. We could see the process distinctly, since she is slow and clumsy, and, in one instance, had difficulty in reaching the fly, falling over to one side in an awkward manner. It is probable, then, that this is a habit with the wasp, but that the sting is usually given at the place of capture.

We opened a number of Bembex nests, but succeeded in raising only one larva, which we took when it was half grown. This one, during the five days that passed before it spun the cocoon, ate forty-three flies.

Mr. Bates has some notes on Monedula signata, which takes nothing but flies, and even confines itself to a single species, although it must sometimes go half a mile away to find it. This reminds us of Pompilus quinquenotatus, which never takes anything but Epeira strix.

ill136

A considerable contribution to our knowledge of the genus Bembex has been made in the paper by Wesenberg (written in Danish) which has already been referred to. This paper deals with Bembex rostrata. It was translated for Mr. Ashmead by Mr. Martin Linell.

ill137

.

It seems that rostrata makes its nest in solid sand, covering it up with loose sand, and usually, also, with a little flat stone, to prevent parasites from entering. The cell measures one cubic inch, the entrance tunnel being one and one half centimeters long, and arcuate. A cell contains four or five fresh flies (Lucilia, Eristalis, etc.), and torn-off wings, sucked-out thoraces, and in the middle of these, a big flat larva.

When the larva is hatched the mother brings more and more flies, the flies being larger and larger as it grows. This adjustment of the size of the fly to the growth of the larva has also been noted by Fabre.

Wesenberg says that fifty Bembecids will nest on a spot as big as a room during a period of three months. The time required for the development of the larva is two weeks, this giving five or six young ones for the season. He queries, “Does each female have more than one nest? and if so, how can she remember them?” To determine this point we marked six wasps by touching them with differently colored paints, putting near their nests pebbles painted to correspond with the owners, and then watched them closely for three hours. During this time the red wasp returned regularly to the red nest, the blue to the blue, and so on. They were watched for an hour and a half on the following day with the same result, so that it seems quite certain that spinolÆ has only one nest at a time. To feed two larvÆ at once, with interlopers thrown in, would be a heavier task than the most determined industry could accomplish.