1911 Encyclopædia Britannica/Wasp
WASP (Lat. vespa), the common name for a well-known sort of stinging insect. The order Hymenoptera is divided into two sub-orders, the Symphyta and the Apocrita. The latter is subdivided into several sections, one of which, the Vespoidea, includes all the true wasps; in addition to the ruby wasps and many of the “Fossores” or digging wasps.
The true wasps (forming the old section Diploptera) are in their turn divided into three families — (1) the Vespidae, (2) the Eumenidae, and (3) the Masaridae, which together comprise some 1500 different species. They are characterized by their wings, which are present in both sexes and also in the modified females or workers, being longitudinally folded when at rest, except in the Masaridae. The antennae are usually elbowed, and contain twelve or thirteen joints; in some cases they are clavate. A pair of notched faceted eyes are present, and three ocelli in the top of the head. The mouth-parts are arranged for sucking, but have not reached that degree of perfection found amongst the bees. Hence wasps cannot obtain the sugary secretion from deeply-seated nectaries, and their visits to flowers are confined to such as are shallow or widely opened; they particularly frequent the Umbelliferae. The maxillae are elongated, and compressed, the maxillary palp six-jointed. The labium is prolonged centrally into a “tongue,” which is glandular at the tip; the paraglossae are linear. The labial palp has three or four joints. The pro-thorax is oval, and its sides are prolonged backward to the base of the wings. The fore wing has two or three submarginal cells. The legs are not provided with any adaptations for collecting pollen. The abdomen is sometimes pedunculate, its second (apparently first) segment being drawn out into a long stalk, which connects it with the alitrunk, made up of the thorax and the first abdominal segment. The queens and the workers are armed with a powerful sting. The usual colour of these insects is black, relieved to a greater or less degree by spots and patches of yellow or buff.
The Diploptera may be subdivided into two groups in accordance with the habits of life of the insects comprising the section. One of the groups includes the family Vespidae, which is composed of social wasps, and includes the hornet (Vespa crabro) and the common wasp (V. vulgaris). The other group contains two smaller families, the Eumenidae and the Masaridae, the members of which are solitary in their mode of life.
Family 1. Vespidae. — In addition to their social habits the members of this family are characterized by certain structural features. The anterior wings have three submarginal cells. The antennae have thirteen joints in the males and twelve in the females; the claws of the tarsi are simple; the anterior four tibiae have two spines at the tip; the abdomen is but rarely pedunculated, and the posterior segments are often very contractile.
The members of this family approximate very closely to bees in their social manner of life. The communities are composed of males, fertile females and workers. The latter are females in which the ovary remains undeveloped; they resemble the perfect female in external appearance, but are slightly smaller. It has been shown by P. Marchal that a clear line of distinction between queen and worker cannot always be drawn. Unlike the hive bees', the wasps' community is annual, existing for one summer only. Most of the members die at the approach of autumn, but a few females which have been fertilized hibernate through the winter, sheltered under stones or in hollow trees. In the spring and with the returning warm weather the female regains her activity and emerges from her hiding-place. She then sets about finding a convenient place for building a nest and establishing a new colony. The common wasp (V. vulgaris) usually selects some burrow or hole in the ground, which, if too small, she may enlarge into a chamber suitable for her purpose. She then begins to build the nest. This is constructed of small fibres of old wood, which the wasp gnaws, and kneads, when mixed with the secretion from the salivary glands, into a sort of papier-mâché pulp. Some of this is formed into a hanging pillar attached to the root of the cavity, and in the lower free end of this three shallow cup-like cells are hung. In each of these an egg is laid. The foundress of the society then continues to add cells to the comb, and as soon as the grubs appear from the first-laid eggs she has in addition to tend and feed them. The development within the egg takes eight days.
The grubs are apodal, thicker in the middle than at either end; the mandibles bear three teeth; the maxillae and labium are represented by fleshy tubercles. The body, exclusive of the head, consists of thirteen segments, which bear lateral tubercles and spiracles. The larva has no anus. The larvae are suspended with the head downwards in the cells, and require a good deal of attention, being fed by their mother upon insects which are well chewed before they are given to the larvae, or upon honey. At the same time the mother is enlarging and deepening the cells in which they live, building new cells, and laying more eggs, which are usually suspended in the same angle of each cell.
After about a fortnight the grubs cease to feed, and, forming a silky cover to their cells, become pupae. This quiescent stage lasts about ten days, at the end of which period they emerge as the imago or perfect insect. The silky covering of the cell is round or convex outwards; and to leave the cell the insect either pushes it out, when it opens like a box lid, or gnaws a round hole through it. As soon as the cell is vacated it is cleaned out and another egg deposited. In this way two or three larvae occupy successively the same cell during the summer. The first wasps that appear in a nest are workers, and these at once set to work to enlarge the comb, and feed the larvae, &c.
The material of the nest, as before stated, is usually dried wood, worked by the mandibles of the wasp, with the addition of its salivary secretion, into a pulp, which can easily be moulded whilst moist; it dries into a substance of a papery appearance, but possessing considerable tenacity. Sometimes paper itself, such as old cartridge cases, is used. The combs are arranged horizontally; each contains a single layer of cells opening downwards. The second comb is suspended from the first by a number of hanging pillars which are built from the point of union of three cells. The space between two combs is just sufficient to allow the wasps to cross each other. The combs are roughly circular in outline, and increase in size for the first four or five layers, after which they begin to decrease; the whole is covered by a roughly made coating consisting of several layers of the same papery substance which composes the combs. This is continued down until it forms a roughly spherical covering for the whole, but not giving any support to the combs, which are independent of it. As the nest increases in size, the covering needs to be repeatedly pulled to pieces and reconstructed, its inner layer being cut away as the combs are enlarged. The covering is pierced by apertures for the passage of the wasps. The cells are hexagonal at their mouths, but above become more rounded in their cross section.
During the first half of the summer workers only are produced, but, as fruit ripens and food becomes more abundant, fully developed females and males appear, the latter often from parthenogenetically developed eggs of the later broods of workers. The males and females are larger than the workers, and require larger cells for their development; these are usually kept apart from one another and from those of the workers. The males may be distinguished by their longer antennae, by the more elongated outline of their body, and by the absence of a sting.
In a favourable season, when the weather is warm and food plentiful, a nest may contain many thousands of cells full of wasps in various stages of development; and, as each cell is occupied two or three times in the course of a summer, those authorities who put the number of the members of the community as high as 30,000 are probably not far wrong.
At the approach of autumn the society begins to break up; the males fertilize the females whilst flying high in the air. They then die, often within a few hours. The workers leave the nest, carrying with them any grubs that remain in the cells, and both soon perish. The nest is entirely deserted. The fertilized females, it has been seen, creep into crevices under stones or trees, or hide amongst moss, and hibernate until the warmth of the following spring induces them to leave their hiding-places and set about founding a new community.
There are altogether, seven species of Vespa met with in Britain. V. vulgaris, the common or ground wasp, V. rufa, the red wasp, distinguished by its reddish-yellow abdomen, and V. germanica, the German wasp, with three black spots upon its first abdominal segment, are classed together as ground wasps. They build their nests in burrows in the ground, but this is not an invariable rule; they may be distinguished from the tree wasps by their shorter cheeks and usually by the first joint in the antennae of the female being black. Vespa austriaca (arborea) is a race of V. rufa, in whose nest it sometimes lives as an inquiline. The tree wasps build stouter nests upon branches of trees; the first joint of the antennae of the females is yellow in front. The tree wasps are V. sylvestris, norvegica and crabro.
The hornet, V. crabro, is the largest species occurring in Great Britain. They have a more distinctly red colour than the common wasp, and a row of red spots upon each side of the abdomen. They occur much more rarely than the common wasp, and appear to be almost confined to the southern half of England. Their nests resemble those described above, but are larger; they are found in hollow trees or deserted out-houses. Their communities are smaller in number than those of the other wasps.
The hornet, where it occurs in any number, does a considerable amount of damage to forest trees, by gnawing the bark off the younger branches to obtain material for constructing its nest. It usually selects the ash or alder, but sometimes attacks the lime, birch and willow. Like the wasp, it does much damage to fruit, upon the juices of which it lives. On the other hand, the wasp is useful by keeping down the numbers of flies and other insects. It catches these in large numbers, killing them with its jaws and not with its sting. It then tears off the legs and wings, and bears the body back to its nest as food for the larvae. Wasps also act to some extent as flower fertilizers, but in this respect they cannot compare with bees;they visit fewer flowers, and have no adaptations on their limbs for carrying off the pollen.
The genus Vespa is very widely spread; it contains over forty species, distributed all over the world. Some of the largest and handsomest come from eastern Asia. V. mandarina of China and Japan, and V. magnifica of the East Indies and Nepal, measure 2 in. across the wings; V. orientalis, found in Greece, Egypt and the East, builds its nest of clay.
The only other genus of Vespidae which is found in Europe is Polistes, which occurs in the countries bordering the Mediterranean. The colonies of this genus are much smaller than those of Vespa. Each nest consists of a single tier of cells in the form of a round plate, supported in the middle by a single stalk. This comb is sometimes vertical, the cells then being horizontal or slightly oblique. Some of the members of this genus store up honey, which in the case of a South American species is poisonous, from the nature of the flowers The members of this genus have a slender body; the thorax is more oblong than in the genus Vespa, the palps are stouter and the abdomen is more distinctly pedunculate.
The genus Ischnogaster, from the East Indies, has many structural features in common with the Eumenidae, but the character of its communities, and its nest, which is very small, justify its position amongst the social wasps.
The genus Icaria, common in Australia and the East Indies, builds very small nests, of two or three rows of cells, hanging on one side from a stalk.
Synaeca is a South American genus, which builds large nests, sometimes 3 ft. in length, closely applied to the branch of a tree; they never contain more than one layer of cells, which are horizontally placed. The whole nest is built of coarse material, chiefly small pieces of bark; and there is only one opening, at the lower end.
Another South American genus, Chartergus, makes a tough nest, pendent from boughs of trees, and opening to the exterior below by a median aperture. The combs are arranged, somewhat like funnels, inside one another, but with spaces between. The apex of each comb is pierced by a hole for the wasps to pass from one gallery to another.
The nest of Tatua, which occurs in Mexico and South America, is also pendent, but the combs are horizontal; the opening from the exterior is at the side, and the passage from one gallery to another is also lateral.
The external appearance of the nest of Nectarina, found in Brazil and other parts of South America, resembles that of the common wasp, but is rougher. Internally the combs are arranged concentrically, more or less parallel with the external covering which affords them support.
The members of the two remaining families, the Eumenidae and the Masaridae, resemble one another in their solitary mode of life; only males and normal females, exist — no workers being found.
Family 2. Eumenidae. — Solitary species, with three submarginal cells in the fore wing; antennae with thirteen joints in the male, twelve in the female; abdomen sometimes pedunculate, posterior segments contractile. In the foregoing structural features the Eumenidae resemble the Vespidae, but they differ in having bifid claws on their tarsi, and the two anterior tibiae have but one spine at the tin. The mandibles are elongated, and form a kind of rostrum, in this respect approaching the Fossores.
Eumenes coarctata is the only British species of this genus. The female is ½ in. long, the male somewhat shorter. The abdomen is connected with the thorax by a long peduncle. The colour is black, relieved by spots of yellow. It constructs small spherical cells of mud, which are found attached to stems of plants, very generally to the heath. At first the cell opens to the exterior by means of a round pore; one egg is deposited in each cell, and a store of honey as food for the larva when hatched; the cell is then closed with mud. The larvae of some species are carnivorous, and then the food-supply stored up in the cell consists of caterpillars and other insect larvae which have been paralysed by the parent wasp stinging them through the cerebral ganglion; when the larva of the Eumenes emerges from the egg it sets up these and devours them.
The genus Odynerus contains a very large number of species, found in all parts of the world. The members of this genus are about the size of a fly, and they differ from Eumenes in having a sessile abdomen. Some of the species construct their cells in sand-heaps, lining them with agglutinated grains of sand; others live in cavities of trees lined with the same material, whilst others build their nests of mud. Like some of the species of Eumenes, they store up paralysed Lepidopterous and Chrysomeleous larvae as food for their carnivorous grubs.
Family 3. Masaridae. — The members of the third family, the Masaridae, are sharply distinguished by the possession of only two submarginal cells in the fore wing, which folds imperfectly or not at all when at rest. Their antennae are frequently clavate, particularly so in the genus Celonites; they are twelve-jointed, but as the terminal joints are almost fused they appear to be composed of only eight joints. The wings are not so completely folded as in the other two families, and the abdomen is but slightly contractile. The maxillae are short and their palps very small, with but three or four joints.
The number of genera comprised in this family is small; none occur in Britain, but in southern Europe some species are found. They make their nest in cavities in the earth, generally in a bank and construct an irregular gallery leading down to it.
During hot fine summers wasps cause a good deal of loss to market gardeners and fruit growers. During this time of year they live almost exclusively upon the sweet juices of ripe fruit, occasionally carrying off small particles of the flesh. At the same time they have not entirely lost their carnivorous tastes, for they frequently attack the meat in butcher's shops, but render compensation by killing and carrying off to feed their grubs considerable numbers of blow-flies. Wasps also perform an important service in keeping down the numbers of caterpillars. The larvae are almost exclusively carnivorous, living upon insects captured by their parents and reduced by them to a pulp before being given to the young. During the spring the first broods that appear live largely upon honey; and this forms the staple food of the genus Polistes throughout their whole life.
In attempting to rid a district of wasps, unless the nest can be taken, there is little good in killing stray members of the community. On the other hand, the killing of queen-wasps in early spring probably means that the formation of a nest and the production of a society whose members are counted by thousands is in each case prevented.
The number of wasps is kept down by numerous enemies. The most effective of these live in the nests and devour the larvae; among them are two species of beetle, Rhipiphorus paradoxus and Lebia linearis. Two species of Ichneumon, and a species of Anthomyia, also infest the nests of wasps and prey upon the grubs. The larvae of the syrphid flies Volucella, found in the nests of both wasps and bees, are now believed to be scavengers rather than parasites. In the tropics some species are attacked by fungi, the hyphae of which protrude between the segments of the abdomen, and give the wasp a very extraordinary appearance.
Bibliography. — In addition to various systematic memoirs enumerated at the end of the article on Hymenoptera, reference may be made to De Saussure (Monographie des guêpes sociales, Genève, 1853-1858), P. Marchal (Arch. Zool. Exp. Gen. (3), iv., 1896), C. Janet (Mem. Soc. Zool. France, viii., 1895) and O. H. Latter (Natural History of Common Animals, ch. v., Cambridge, 1904).