WORKERS IN CLAY

THE nests of PelopÆus coeruleus and PelopÆus cementarius, our two mud-daubers, are common under eaves and in other sheltered places, and many a country boy on opening them has been astonished to find that they do not contain wasps, but are crammed with spiders. Let them alone, however, and the wasps will arrive, for somewhere in the mass is an egg; and when it hatches the spiders will serve as breakfast, dinner and tea for the larva, until the change from the Arachnida to the Hymenoptera has been accomplished. Poor spiders! it is a wonder that there are any left, such thousands and tens of thousands are destroyed by these tremendously energetic enemies.

Of what is PelopÆus thinking as, humming loudly, she jams her paralyzed and benumbed victims into her little cylindrical tubes? If only we could get inside of that little head! If only we could be wasps for a day, and then come back and tell about it, how much vain speculation would be saved! We can understand her when she soars gayly into the blue, the sunshine flashing from her brilliant wings; we too have felt the delight of health and freedom. She is still comprehensible when, at the close of day, she and her sisters quarrel for the favorite sleeping-places among the carvings of the porch pillars; but we cannot follow her mental processes when, at the moment of building, she surrenders herself to the mysterious sway of instinct, doing she knows not what, but doing it joyously, and preserving through it all the precious possession of her own individuality. Every aspect speaks of pleasure as these wasps gather at well or spring, and, singing contentedly, stand on their heads to gather their loads of mud. Briskly and gayly they fly back and forth, pausing at the nest long enough to pat the soft building material into shape. A single load makes half a ring at the larger part of the nest or a whole one at the bottom; and since one dries before the next is put on, the contour of each ring is visible when the tube is done, giving a very artistic effect. This is only accident, however; the wasp cares nothing about the beauty of the structure, for her next step is to daub the whole with lumps of mud, the walls being thus thickened and strengthened. About forty loads are necessary for each cell, and to build and provision one is a good day’s work.

It is strange enough that with no one to teach her PelopÆus knew how to make her cell; but now she must do her hunting, and it is stranger still that she should be impelled to catch nothing but spiders. How does she know a spider from a fly, and why should she prefer one to the other? Not so unreasonable as some wasps, however, she demands nothing further than that her prey shall belong to this great group, and passes lightly over differences of species and genera. Her powerful sting fits her to cope with anything she may meet; but as the size of the cell must be taken into consideration, and the victim must be carried home on the wing, she is on the lookout for something not too large. Here then she ceases to be an automaton, and to some extent makes use of her wits.

How does PelopÆus seize her spider? When and how many times is it stung? Is the wound given with discrimination, a certain point in the ganglion being pricked, so that the spider may be paralyzed, but not killed? Is there any malaxation?

These were important questions to us, and we were therefore greatly excited over our first hunt. One of the blue wasps came flying along, alighted on our cottage wall, and began her search, creeping into corners and cracks and investigating cottony lumps of web. In a few moments a small Epeira strix (the only species to be found on the cottage) was dislodged, and at once dropped to the floor of the porch. The wasp paid no further attention to it, but went on with her search. Three more spiders, one after the other, were disturbed and dropped to the floor without being followed. The fifth one discovered was a little larger than the others, and was seized by the jaws and first legs of the wasp before it had time to escape. It was then rolled into a ball, or at least so it appeared, and stung, then rolled a little more and stung again, and then carried off. We had scarcely drawn breath after this performance when a second wasp appeared. This one dislodged two spiders, and then caught a third, which was seized and stung without any rolling, and then instantly borne away. A third wasp seized the first spider that she found, and started on her flight at the same moment, stinging it on the wing.

So the game went on, while we waxed warm with the excitement and fascination of the chase. As the hours went by some of the yellow mud-daubers appeared, adding to the interest of the scene, although we could not see that their method differed in the least from that of coeruleus.

Rarely did they succeed in catching a spider until they had dislodged two or three. Sometimes the spiders were followed as they dropped, and were caught on the floor, but oftener the wasp let them escape and continued her search on the wall. At the moment of capture we could see that she bent her abdomen under and inflicted a sting, but although we concentrated our attention on the point we could not be sure as to just what part was touched. It is our impression that this first sting was given anywhere, at random, with the object of producing a condition of temporary quiet in the victim, so that the next part of the operation could be carried on with deliberation.

The second step in the procedure was commonly for the wasp to alight upon some neighboring object, usually the branch of a bush or tree, and sting the spider a second time, being evidently in no haste; but the difficulty of following her as she flew, and her habit of alighting above our range of vision, made it almost impossible to see just what she did. She certainly remained on the branch for some moments, either resting quietly or rolling the spider around and around, and had every opportunity to sting it as carefully as she wished; but we afterward found that she followed no exact method, since two thirds of the spiders were killed at the moment of capture, and most of the others died within a week, while a few lived for thirty-five or forty days. In this study we opened five hundred and seventy-three cells and handled over two thousand spiders, watching over them from day to day with a magnifying glass, that no sign of life might be neglected.

When PelopÆus has filled her cell, she seals it up and makes another close to it, clusters of from six to twenty being found in one spot. Any especially desirable place is used by great numbers; and they make a lively scene, working eagerly at their nests, dashing off for more mud or bringing in their victims. All animated by the same compelling instinct, they are still individuals, and the character of each enters into her work. One picks up the first spider she sees, no matter how tiny it may be, and makes twenty-five or thirty journeys before her cell is filled, while another seems to have a calculating turn of mind, using four or five big spiders instead of a quantity of small ones. Has she made a note of the calibre of her cell, and determined to save herself trouble by looking farther and selecting the largest ones that will go in?ill271

Most of them place their cells vertically; but a few prefer the horizontal position, while still others, undecided as to the matter of direction, make clusters in which some are horizontal and others upright. Occasionally there is a remarkable innovation in building-material, as where in a group of fifteen, four cells in the centre were constructed of pure white plaster, forming a striking contrast to the surrounding mud color. One wasp built an entire cluster after an original fashion, following the beaten track until the cell was completed, and even bringing mud enough to daub it over, as her sisters were doing, but sticking it all in one spot, so that when the group was complete irregular lumps were attached here and there, leaving visible the elegant architecture of the individual cells. Did she think they were too pretty to spoil? or was she merely one of those radical spirits that rebel against conventionality and demand change for the sake of change? It is these variations that furnish Natural Selection with its materials; but rigid as may be the rules regarding the non-survival of the unfit, we find that the race of PelopÆus still produces many absent-minded wasps, that after spending hours in carefully constructing their nests, seal them up empty, forgetting to put in the spiders or to lay the egg.

When a cell is sealed, the mother wasp ceases to take an interest in it, but she has done all that is necessary. In two or three days the egg hatches, after which the larva spends ten or fifteen days in eating, and then spins its cocoon. Here it remains, perhaps for only a few weeks,—for there are two or three generations in one season,—or perhaps through the long months of winter.

Fabre gives a most entertaining account of a French species of PelopÆus which nests in the wide-mouthed chimneys of the peasant. Undisturbed by the steam of washing day or the bustle of dinner-getting, the wasp enters the open door, passes unconcerned among the human inhabitants, and makes her cells against the smoky bricks, out of reach of the flames. This species kills her prey at the moment of capture, by which act she falls in the estimation of Fabre, who respects a wasp in proportion to the nicety with which she delivers her sting. He says, however, that at least she follows a logical method in turning to account these spiders, menaced with early decay. In the first place the prey is multiplied in each cell. The piece actually attacked by the larva is soon a disorganized mass, likely to decay speedily; but it is small and is consumed before decomposition can advance, for when a larva once attacks a spider it does not leave it for another. The others then remain intact, which is enough to keep them fresh during the short period of larval life. When, on the contrary, the prey consists of a single large piece, it is necessary that the organic life should be maintained, and a special art must also be observed in eating it. It is well then that PelopÆus is inspired to take numerous small pieces. The egg, moreover, is always placed on the first spider brought in, whether the storing of the nest is completed within a few hours, or whether, as in some cases, it occupies several days; and this M. Fabre considers a very happy arrangement.

The French PelopÆi differ from ours at nearly every point. Ours kill only about two thirds of their victims, many of the others being paralyzed so perfectly that they live for two or three weeks. Again, ours, instead of placing the egg upon the first spider, almost invariably lay it upon the last one brought in. Another point of difference is that our larvÆ frequently start in by eating up the soft abdomens, like children who first devour the plums in their pudding, returning later to the tough parts that are left, a rash and reprehensible course of action of which their better-taught French cousins are never guilty. When one comes to compare the two sets of facts furnished by the two groups of species, the deductions which Fabre has drawn as to the importance of the instincts of the French group are seen to be unfounded. The American species violate nearly every principle which he considers necessary to their existence, and yet they flourish and multiply. For our part we find nothing in the actions of PelopÆus that needs to be explained—nothing that is not well adapted to the conditions under which each species works. The measure of praise or blame which we mete out to these depredators is merely a way of saying whether we would or would not follow their methods in provisioning our houses and rearing our children. Perhaps we would always use large spiders and would always have them fresh; but it is evident that tastes differ, and the matter is so purely a subjective affair that it will have to go unsettled. In any event, whether her victims be strong or feeble, old or young, big or little, fresh or dry, they certainly serve admirably in enabling PelopÆus to rear brood after brood, and to people the different parts of the earth with abundant representatives of her kind.