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Popular Science Monthly/Volume 49/September 1896/Social Insects

SOCIAL INSECTS.
By L. N. BADENOCH.

IT is well known that some bees are social and form nests where their broods are reared, workers existing who provide daily for the young. In architectural skill these social kinds do not always hold a foremost place. The cells composing their nests vary in shape from the perfectly hexagonal, as in the hive, to those which are less regularly six-sided, until in the bumblebees' homes they are not in the least like the delicate, sharply defined structures of the true honeybee, but are oval and isolated or distributed almost at random.

Leaving the hive bee out of the question, the bumbles (Bombi) alone construct social communities in England; they constitute the nearest ally, as regards its habits, of the true honeybee in North America, which is especially rich in species. Their economy is simple; their colonies begin, enlarge, and end like wasps. They live for one season, perishing with the cold of autumn, except a few queens, which hide themselves away in utter solitude in sheltered and convenient spots, and, awaking with the warmth of spring, lay the foundation of a new swarm. In the ordinary course of things these queens do not survive a second winter.

Parasitic bees (Apathus) so closely resemble the bumbles that it requires long practice to distinguish them easily. Little is known of the parasite, other than that it is found in the nests of its hosts, at whose expense it apparently lives, after the manner of the cuckoo. It has no pollen basket, showing that it can not collect food, and its young must feed upon the stores of their hosts, and its jaws seem unadapted for building. Flies and several beetles also prey upon the bees, and the larvæ of moths consume their honey and waxen cells.

In the tropics the honeybee is replaced by the Meliponæ and Trigonæ, which are generally minute and almost stingless, and live in vast colonies. The former construct a comb for their young, resembling that of the hive, but of one layer of cells, while the honey cells are irregular and occasionally attain a great size. They nest in hollow trees or in banks or any suitable crevice; the Trigonæ, suspend pear-shaped combs from the extremities of the branches of trees, without any kind of external PSM V49 D664 Nest of polistes.jpgFig. 1.—Nest of Polistes. A wasp's nest without cover. covering. Meliponæ are masons and prone to block up the gap in the tree they employ with clay, leaving a small orifice for entrance and exit; some stop theirs with wax, and they incline to feed on the sweet sap that exudes from the forest trees and on the excrement of birds rather than on flowers. As with the communities of social bees, so with the social wasps (Vespidæ), there appears a third order of beings, the workers or neuters, which, like the females, are provided with a sting. The interest attached to the economy of the family rivals that of the wonderful works of the hive; indeed, many of the structures of the social wasps constitute the most beautiful examples of insect architecture. Among them there is a variety of form, an evidence of intelligent choice of the materials used in their construction, a difference of texture produced, and an adaptation of the nest to the circumstances of the situation to which the buildings of the bee can lay no claim. If the hive bee is the more admirable architect, it is decidedly not the most ingenious. It is the better mathematician, but the less facile engineer; it is the more learned, but the less imaginative. While the bees may be said to build in wax, the social wasps are chiefly natural paper or cardboard makers—not out of rags, but ligneous materials, triturated and agglutinated in various ways. Though the nests are upon many plans, essentially they are all alike. Similar cells, nearly always hexagonal, are agglomerated, leaving between them no space to form combs, after the manner of bees, but of very varying aspects. These are the cradles of the larvae, which, deposited here as eggs, are reared by the female or workers, and, having attained full growth, they inclose themselves within the cups, with silky convex caps, until their transformation to perfect wasps.

So far as the disposition of the social wasp is concerned, it is a case of being given a bad name, and—well, maltreated. But a wasp seldom attacks when unmolested; yet threaten its citadel, and you will probably have cause to repent, for, with courage that we all must admire, it boldly and persistently resents intrusion on its dwelling and defends against disturbance its helpless young brood.

It combines the most opposed instincts of diet, and is an omnivorous feeder. From the first days of spring till autumn ends, we may see wasps (Vespa) intent upon stealing the sweet vegetable liquor they love; in spring they profit by the blossoms of fruit trees. As the fair profusion of summer changes to the soberer autumn wealth, they are presented with another fertile source of PSM V49 D665 Home of myrapetra scutellaris.jpgFig. 2.—Home of Myrapetra scutellaris. nutriment, and it is then their colonies immensely increase. They fall upon fruits voraciously, the choicest and most ripe, and so have gained for themselves a worse reputation than insects much more injurious. Should the season be warm and the increase of their colonies commensurate with the warmth, as it often is, they become a veritable plague, not only in gardens, but at table they agitate us while they nibble at some luscious dish.

But, hateful marauder though the wasp is in these respects, it is a predaceous as well as a vegetable eater, and thus not devoid of the compensating quality of usefulness in ridding us of many a fly and other pests. The audacity with which it seizes and devours insects is astonishing. The attack is sudden: it will spy a fly on the leaf of a bush, and in the twinkling of an eye is upon it; if large, it is dismembered; head, wings, and legs are torn off, and the trunk is demolished on the spot or borne away. Wasps often attack butterflies of different kinds; pouncing upon the luckless victims, as a falcon on a bird, they drag them to the ground and mutilate them, and subsequently the mangled body seems to be robbed of all vitality ere the wasp takes its final departure with it to the nest. Curiously, if it misses its aim, it does not strike a second time, but flies on, as if to cover its defeat. Immoderately fond of honey, it frequents the vicinity of beehives, ready to swoop on the bees returning home charged with their hard-got spoil.

Social wasps have two principal modes of nidification. Either the combs are enveloped in a covering of simple leaves of generally slender paper, analogous to that which serves for the cells; or the covering is of cardboard, composed of only one layer of material, of a consistence at times extraordinarily thick and resisting, at others slight and supple.

The common paper-makers build in the open air, on trees or bushes, under the roofs of outbuildings, on a beam, or in some such situation; the construction corresponds with that of the ground wasps, but the texture of the foliaceous envelope, which is fabricated with perfect art, has all the appearance of shell-work. It incloses an infinity of cells arranged in many tiers. A nest is invariably built from above downward. The start is made by accumulating on the determined site a good supply of paper, forming it into an umbrellalike canopy. To the under side of this cap—the ceiling, so to speak—the first comb is attached, and the rest of the work consists in prolonging the canopy more or less in an egg-shape, and in establishing additional combs, free, as a rule, only pendent to columns of paper, which pass from the upper surface of each comb to the comb immediately above; entrance is obtained at the lower end. Toward the summit of the envelope is a thickened cellular mass, but this portion excepted, it is made up of a number of separate leaves or layers of paper, limited in size and imbricated, and in contact together merely at the points of imbrication, leaving large cellular spaces between the sheets; moreover, the points of fusion of two successive sheets never fall one over the other. Each sheet therefore lies on a stratum of air, with the result that the exterior layers may be soaked with rain without soiling in the least the ones beneath. Tree wasps increase the size of the combs by cutting away the inner layers of the envelope, taking care to add layers externally so as to maintain, and even to slightly augment, the thickness of the walls, in proportion to the greater magnitude now assumed by the edifice.

Some elegant and graceful pensile nests, although diverse in form, have this in common, that the combs are always destitute of any envelope; and the cell-group is supported by a stalk of paper. which may be central or wholly lateral. Usually a varnish is rubbed on the cells to prevent them being wetted by rain (Fig. 1).

The envelope of a typical cardboard-maker (Chartergus chartarius) is of a veritable cardboard, white, gray, yellow, or buff in color, smooth and solid, and impervious to the weather. It may be conical, cylindrical, almost globe-shaped, straight, but more often is a little curved. In the interior the platforms of cells differ from those of the common paper-making wasp in stretching right across like so many floors, being fastened on all sides to the walls. A simple hole perforates each, enabling the wasps to get from story to story. The form arises from the mode of enlargement of the dwelling. When the number of inhabitants becomes great and a fresh series of cells is required, these wasps do not, as a preliminary proceeding, amplify the envelope so as to extend the tiers; they first build cells, and cover them afterward. Beginning with the bottom of the nest, they set cells upon it, then lengthen the outer wall so as to include this fresh stage, and close in the end with a new floor, in its turn to become the ceiling of the next tier of cells when enlargement is again desired. No trace of the addition is suffered to remain and mar the covering, which would seem constructed at one stroke. Probably these wasps, like Myrapetra scutellaris (see Fig. 2), deviate from the ordinary habits of wasps in being collectors of honey.

It would be difficult to find a more peculiar nest than that of Myrapetra scutellaris. It is huge as compared with the insects, its brown cardboard wonderfully thick, hard, firm, and coarse in texture, and composed, not of wood fibers, but of the dung of the capincha, an aquatic cavy. The strange, fairly conical knobs that beset the surface of the envelope may defend the abode, which hangs low, against mammalia, such as tigers, jaguars, and cougars, that would plunder it of its honey; they appear to protect and conceal the entrance ways—of which, opposed to the custom of wasps, there are many—but they may be simple freaks of Nature. It seems odd for beings so sensible to put these projections on the end of the nest, no less than on the sides, necessitating their gnawing them away each time they add a stage; but probably they possess some means of softening the cardboard, and doubtless the same material, worked up afresh, helps to establish the new tier and the new cells.

 


 
It is represented in a bulletin of the Department of Agriculture that about two hundred and fifty thousand cocoanut palm trees of all ages are growing on the eastern coast of Florida, about twenty-five thousand of which are bearing. The tree is fruitful near the salt water, but does not thrive when removed inland. It begins to fruit in from five to seven years after planting the nut.