Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/591

575 HYMENOPTERA 575 are the workers or neuters, undeveloped females on whom the work of the colony depends ; and, lastly, there are the males. It is with ants that the workers are most pro foundly modified. They are wingless, and there may be in a colony several sorts, each kind performing different duties, and having the body modified in accordance with the work it has to do. Those which act as soldiers (when a special kind is set apart for this work), for instance, have the mandibles enormously developed ; another set may secrete honey for the benefit of the others, &amp;lt;kc. J of The Hymenoptera must be regarded as one of the most ] rder beneficial and useful to man of the insect orders. The pro- duce of the hive bee wax and honey has been employed by man since the earliest ages, and forms an extensive article of commerce. The curious structures raised by Cynipidce on the oaks of eastern Europe galls have long been used in the manufacture of ink. But, whatever the bee may have done in contributing to our luxuries, and the gall-fly in rendering easier the advance of knowledge, these are small benefits compared to the indirect advantages we de rive from the labours of the parasitic species through the hwoc they make among the insects which devour the pro duce of our fields and gardens, and too often destroy the labours of the farmer and gardener. When we remember that there are vast numbers of insects which destroy plants ; that many of these are so minute and obscure in their mode of life as to escape ordinary observation, save when the in jury is done; and that others appear in enormous numbers, it becomes evident that an insect which causes the death of a single caterpillar does good service, since that caterpillar would have (if left undisturbed) given, in all probability, origin to an imago which might give birth to hundreds of others. It is this which the ichneumons do, they destroy the larva; of plant-devouring insects. Another division of Hymenoptera does equally good service. It has been shown by modern researches that without the aid of bees many flowers would never yield seed. Many plants cannot fertilize themselves, so that if bees did not carry the pollen from one plant to another, and thus effect fertiliza tion, no seed would be produced. The red clover, for instance, would, never produce seed if it were not for the humble bees fertilizing it in their visits in search of honey. It must, however, be confessed that some Ilymenoptera do very considerable damage to vegetation, especially saw-flies and ants. Of injurious saw-flies the most destructive are Eriocampa adumbrata, on f ruib trees ; Nematus ribesii, which is so destructive to the gooseberry and red currant ; Athalia spinarum, at one time so destructive to the turnip (probably when it first took to feeding on it) ; and Cephus, in the stems of corn. The damage done by ants in Europe is small ; but in the tropics the leaf-cutting ants do enor mous damage by cutting down the leaves of trees (especially cultivated ones), which they convey into their nests, where they are used (according to Belt) to rear fungi upon which the ants feed. atic The Hymenoptera are almost exclusively dwellers on land, les&amp;gt; and are essentially sun-loving insects. Two or three only live an aquatic or quasi-aquatic mode of life. Sir John Lubbock discovered two minute species of Oxyura (Poly- nema) which descend into the water for the purpose of depositing their eggs in the eggs of aquatic insects. They use the wings as oars to swim in the water, and can remain in it for two hours. An ichneumon (Agrioti/pes) has long been known to live as a parasite in the bodies of caddis- worms ; and it has been observed to go down into the water to find the worms, which are said, when infested by the ichneumons, to anchor themselves by means of a silken thread. ssion Many Ilymenoptera give origin to sounds. The humming mn(i - of bees is one of the most familiar and delightful of country sounds. It is not yet quite clearly understood how it is caused, but there is evidence enough to show that the buzzing originates by the air impinging against the lips of the metathoracic and abdominal stigmas ; although it is possible, too, that the rapid vibration of the wings (224 per second with the Bombus rnuscorum and 440 with the honey bee) may also have something to do with the production of sound, for a bee can give out differently pitched notes according to its mood, as it is pleased or angry. Besides the buzzing sounds, a few other species chirp by means of the abdominal segments. Mutilla stridulates by drawing in and out the raised striated surface of the third under the edge of the elongated second segment. The workers of Myrmica stridulate in pretty much the same way. The internal anatomy of the Hymenoptera presents some Internal interesting features. Their organs of secretion are numer- anatomy, ous. The poison is secreted in two long ramose tubes; and from them it goes into a sac situated near the base of the sting. Wax is made in some of the abdominal segments. 1 The salivary glands in the hive bee (worker) are very large and complicated. They are three in number, two (an upper and a lower) placed in the head, and the other in the front region of the thorax. Each gland is different, and has excretory ducts of its own. In the queen bee these are not nearly so much developed as in the worker, and they are even less in the drones. Many saw-fly larvae secrete fluids for purposes of defence. Some species of Tenthredo secrete a blackish liquid, which they eject from the mouth; Perga throws out a gummy matter from the same orifice, and Cimbex an acid liquid from lateral pores. Then there are the silk-secreting glands which most larvae possess. The urinary vessels are always present, and may be as many as 150. According to Von Siebold, the aculeates have a long intestine and a stomach with many convolutions, while they are sbort in the terebrant forms. The tracheae are well developed. Many dilatations are given off from the main stems, a pair at the base of the abdomen being exceptionally large. In connexion with the female organs of generation, it is worthy of remark that sebaceous glands and a copulatory pouch are absent in the Aculeata, although present in the other section. The ovaries are two in num ber, and consist of a number (it may be as many as a hundred) of distinct many-chambered tubes. Each tube in Athalia, for instance, contains 7 eggs, and, as there are 18 of such tubes in each ovary, there will be thus 250 eggs in all. In Platyyaster the ovary is of a very exceptional nature, inasmuch as the egg tube is a close sac, so that it is burst when the egg is laid. The most noteworthy and exceptional features in the Special- developmental history of the Hymenoptera are those shown ties in by some very minute species of Oxyura, which live in the eve .l ( bodies of Diptera (Cecidomyia], and in the eggs of beetles and dragon-flies. After the eggs of Platygaster have undergone segmentation, and the embryo has been formed, there leaves the egg a larva of a very unusual form. It is broad arid rounded at the head, but contracted towards the tail, which terminates in four spined, bristle-like appendages, so that the larva has a considerable resemblance to a copepod. It is provided with a mouth and hook-like man dibles, by the aid of which it anchors itself inside the body of its host (the larva of a Cecidomyia) ; there are a rudi mentary stomach and antennae, but no trace of nerves, tracheae, or organs of circulation. Soon it changes its form: the tail with its bristles is thrown off; it becomes shaped somewhat like a hen s egg ; the nervous, circulatory, and reproductive organs become visible, while the alimen tary organs show an advance in structure. This second 1 The wax is secreted on the ventral surface of the hive bee, hut on the dorsal surface with the stingless bee of America (Melipona).