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thousands upon thousands of individual insect enemies, but is affected by scores and even hundreds of species. A tabulation of the insect enemies of the apple already recognized in the United States shows 281 species, of clover 82 species, and of so new a crop as the sugar-beet 70 species. The insects of the vine or the orange, of wheat, and in fact of all of the prominent staples, show equally startling figures. It is this damage done by insects injurious to agriculture that has given rise to the comparatively new branch of applied science known as economic entomology, which, although originating in Europe, has been encouraged to such an extent in the United States, owing partly to the greater necessities of a new country and partly to the practical turn of mind of the American, that there are more official economic entomologists employed by the States and by our general Government than in all of the other countries of the world together.

Aside from cultivated crops there is hardly any product of man's ingenuity which is not damaged directly or indirectly by insects-the timbers of dwellings, household utensils, clothes, nearly everything used as food, books, furniture, and drugs, and an infinite variety of other use ful substances. They are very injurious to live stock and other animals; practically every species of animal which has become domesticated and is of value to man possesses its insect parasites and enemies. Some of them are general parasites of warm-blooded animals; others are specific to the animals or groups of animals which they affect. Horses, cattle, and sheep all have insect enemies which are not only very deleterious to their health, but frequently cause their death in numbers. The bot-fly of the horse lives in the larval condition in incredible numbers in the stomach and intestines of the horse. The bot-fly of the ox lives, in the larval stage, under the skin of the backs of cattle, and by its perforations ruins their hides for commercial use. The bot-fly of sheep inhabits the nasal and orbital sinuses of sheep and produces insanity and death. (See BOT.) The horn-fly, the numerous gad-fly, including the tsetse-fly of Africa, the screw-worm fly of the Southwestern United States (qq.v.), and many others, seriously hinder

the efforts of the owners of live stock.

INSECTS AND DISEASE. As annoying man him self, insects play an important part, since there are very few regions of the habitable globe where man is not troubled by them. Bedbugs, fleas, lice, the itch-mite, the screw-worm fly, mosquitoes (qq.v.), and many other species unite in this method of damage to the human species. It is, however, as carriers of disease that insects are perhaps of the greatest importance in their relations to the human species. The filaria diseases of the East (elephantiasis, chyluria, and lymph scrotum) are transferred by certain mosquitoes; the Texas fever of cattle in the United States, the red-water diseases of Africa, and other cattle fevers are transmitted by certain ticks; the tsetse-fly of Africa carries the micro-organisms of disease; the purulent conjunctivitis of the Egyp. tians and Fiji Islanders is communicated by the house-fly; the eye disease, known as 'pinkeye' in the Southern United States. is transported by minute flies of the genus Hippelates. Asiatic cholera and typhoid fever are carried by the house-fly; and it is claimed that the bubonic

plague is spread by fleas. All forms of malaria are carried about by mosquitoes of the genus Anopheles (see MOSQUITO), and yellow fever by those of the genus Stegomyia. (See MOSQUITO.) It has also recently been claimed that dengue fever is in Syria spread by a mosquito of the genus Culex; that Anthrax bacilli in malignant pustules in human beings are caused by the bite of flies of the genera Tabanus and Stomoxys; and that the famous 'surrah' disease of cattle in Oriental regions is also carried by gad-flies. POISONOUS INSECTS. Certain insects may be considered under this head which poison human beings in any one of several different ways: (1) They may have a sting which is a modified ovipositor, and which is connected with a specific poison-gland, as with the bees, wasps, stinging ants, and certain other Hymenoptera. (2) There may be a modified salivary gland which has a poisonous secretion and is connected with a piercing beak, as with certain bugs of the order Heteroptera, and as with many dipterous insects like mosquitoes and other biting flies. (3) The hairs covering the body surface may be modified into sharp bristles, which may be simple or barbed, and which, when coming in contact with the skin of human beings, produce an urticating or nettling effect. Poisonous insects of this group are confined to the caterpillars or larvæ of certain moths, especially of the family Limacodidæ, and, to a much less marked extent, a few of the caterpillars of Bombycidæ, such as Orgyia leucostigma, Euproctis chrysorrhoea, as well as to a few of the Saturniidæ, like the larva of the Io moth. (4) Certain beetles when crushed produce a blistering effect upon the skin. These are confined to the family Meloida or blisterbeetles (q.v.).

The poison of bees is formed by the mixture of the secretions of two glands, one of which is acid and the other alkaline. With the burrowing wasps the alkaline gland is absent or atrophied, and the poison consists only of the acid. The effect of the sting of these wasps is to stupefy the prey and not to kill it. It results that the insects stung remain in excellent condition as food for the larvæ of the wasps for a considerable length of time. (See WASP.) The severity of the sting of the aculeate Hymenoptera and the with different species. The sting of our large amount of poison injected into the wound differ mud-wasp (q.v.) is especially severe, and as a rule the stings of wasps have a more poisonous effect upon human beings than the stings of bees. There are cases on record where many bee-stings on the same individual have produced death. Several instances have been well authenticated by medical men of the death of a human being from a single sting of a wasp, the sting acting as a very powerful irritant poison on the nervecentres of the patient. As a rule such cases are confined to exceptionally nervous individuals, to those inheriting gouty tendencies, who remarkably susceptible to the action of certain medicines. Persons handling bees and wasps become immune to their poison; the stings have little effect upon them. This immunity, however, disappears in the absence of continuous reinoculation. This fact is well known to beekeepers, and entomologists who collect wasps and other stinging Hymenoptera in large numbers have called attention to the same fact. The rem

are

edy for the stings of both bees and wasps is the immediate application of an alkali.

Many of the poisonous flies are treated of under MosquITO; GAD-FLY; and BLACK-FLY.

The true bugs which give a poisonous bite with a piercing beak, and which may attack man, belong almost entirely to the family Reduviide (see CONENOSE), to which the terms 'piratebugs' and 'kissing bugs' are applied. The Eastern species are Opsicates (or Reduvius) personatus, Melanolestes picipes, and Melanolestes abdominalis; and the principal Southern and Western forms are Rasahus biguttatus and Conorhinus sanguisugus. (See the article CONENOSE.) The bite of these bugs is specifically poisonous, but the great inflammation which so often occurs is doubtless due to the entrance into the circulation of germs of putrefaction, since the bugs are attracted to dead animal matter. The Eastern species (Melanolestes picipes) is a shining black bug rather more than a half inch in length. The principal Western species (Rahasus biguttatus) is reddish in color with blue-black fore wings, each marked with a round reddish spot. This latter species is, according to Davidson, the cause of nearly all of the supposed cases of 'spider-bites' in the Southwest.

ECOLOGY. As a class, insects are represented in practically all parts of the world. While flourishing more abundantly in the tropics, they are found in countless numbers in the temperate regions, and are also very numerous in boreal regions. They abound inside the Arctic Circle, and in the short Arctic summer many species of nearly all orders may be collected. As a rule, as with other classes of animals, the forms occurring in tropical regions are larger in size and more brilliant in color. Many groups are confined to the tropics; others have a wide geographic distribution. The value of the class Insecta in the study of the geographic distribution of life is very great with certain groups, while others have comparatively slight faunistic value. Civilization exerts a direct and destructive influence upon the insect faunas of large regions. Insects being largely dependent, directly or indirectly, upon vegetation, the destruction of the wild flora and sylva and the introduction of cultivated crops almost immediately change completely the characteristics of a given insect fauna. The rapid development of methods of transportation, and especially intercommunication between remote regions, by means of the constantly increasing number and speed of vessels, has resulted in the accidental introduction and acclimatization of many hundreds of species of insects into regions remote from their original homes, many of which succeed in establishing themselves. The facility of acclimatization varies greatly with different groups, and this facility is dependent upon the degree of simplicity of the life of the insect and upon the degree of simplicity of its natural environment. So great has become the danger of the introduction of injurious species from one country to another during late years, that many nations seek to protect themselves by special quarantine

measures.

From what has preceded, it is evident that insects, in spite of their small size and their consequent slight strength, have been remarkably successful in the so-called struggle for existence. They have a long geological history, and the in

sects of Tertiary rocks are in some instances almost generically related to living forms. Rapidity of growth and power of multiplication have been prime factors in this persistence, while the relations which exist between circulation and respiration have been almost equally significant. In many instances the growth from the egg to the individual occupies only a few days, while in some species a single female will lay several thousands of eggs. The functions of circulation and respiration are so related that nutrition can be carried on very rapidly and very efficiently. By the phenomenon of metamorphosis, growth and development are isolated from one another, allowing growth to go on unchecked and uncomplicated by development.

The social life of insects is very remarkable; organized societies are formed with many species, especially the Hymenoptera (bees, wasps, and ants) and the Isoptera (white ants or Termitidæ). In these societies great numbers of individuals live together and are greatly modified in structure in accordance with the different functions which they perform in the community. See ANT; BEE; WASP; TERMITE; and Social Insects, below.

REPRODUCTION. Nearly all insects undergo in the course of their lives remarkable changes in form. A few forms are ovoviviparous-that is, bring forth living young, but the great majority lay eggs. (See EGG.) With some forms there is a development without metamorphosis, and in these the young insect just hatched from the egg is of the same form as the adult insect. With others there is what is termed an incomplete metamorphosis-that is to say, where, although the young greatly resemble the adult, there is still a striking change of form during life. With others still there is what has been termed a complete metamorphosis (q.v.), in which the young just hatched is strikingly different from its subsequent stages. With the bees, butterflies, flies, beetles, and other insects, the form which hatches from the egg, and which is known as the larva,' is a 'grub' or a 'caterpillar.' This, after reaching full growth, passes into another form, which is known as the pupa, and in which in the majority of cases the insect is quiescent, while from this stage there eventually emerges the perfect insect. Larvæ grow by molting; the skin is more or less hard and is composed of chitin; a new skin is formed beneath the old skin, which eventually bursts and permits the larva to emerge. The number of molts differs with the larvae of different groups and ranges from two or three to as many as twelve or more. The phenomenon known as hypermetamorphosis sometimes occurs. With certain of the blisterbeetles, for example, the first larvæ which are born possess legs, by the aid of which they can cling to a bee and be carried to its nest, where they will live on the food stored by the bee; after a molt they lose their legs and become almost organless, floating about in the honey. Later still, another form of larva is found. See METAMORPHOSIS (in Animals); LARVA; PUPA.

SOCIAL INSECTS. A great many insects lead solitary lives. Others, either as larvæ or as adults, are gregarious, and in gregarious feeding and gregarious life we have the beginning of social communities. Many lepidopterous larvæ, or caterpillars, feed together in great masses, like the army worm (q.v.) of the United States, and

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6 ICHNEUMON FLY ICHNEUMON JUCUNDUS

7 SPOTTED LADYBIRD - MEGILLA MACULATA

8 GREEN CATERPILLAR-HUNTER - CALOSOMA SCRUTATOR STIRETRUS ANCHORAGO

No. 3 ENLARGED NEARLY TWICE, Nos 7 AND 9 GREATLY ENLARGED

more especially the larvae of certain silk-spinning moths, like the European processionary moth (Cnethocampa processionea), and less markedly the American tent caterpillar and fall webworm (qq.v.). These tents or webs for community feeding are carried to a higher degree of perfection in the European tineine moths of the genus Hyponomeuta, and still more perfectly in the community nests of a tropical butterfly (Eucheira socialis). A number of moths make communal cocoons, but nearly all of these are tropical. The beginning of a true communal life is seen with the ambrosia beetles (q.v.) of the family Scolytidæ. These are beetles which make galleries under the bark of trees, apparently cultivating a fungus which they use as food, preparing a bed for its cultivation; they also carefully remove excrement from the fungus gardens and practically bury their dead. The most perfect socialism, however, occurs among the bees, wasps, and ants of the order Hymenoptera, and among the termites or so-called 'white ants' of the order Isoptera. Not all bees are social. A large group is composed of solitary bees. Among the social bees a more or less primitive social life is found with the bumblebees. Here there is a communal existence. Nests are made, cells are constructed for the young, the young are fed by the adults, and there is a separation into three castes, viz. females, males, and drones. There is also the beginning of a separation of the drones into two castes, the larger ones in general attending to the mending of the covering of the nests and to the ripening of the honey, while the smaller ones for the most part do the inside housework, such as the wax-repairing and the nursing of the young. The community life of the hive or honey bee is much more complicated than that of the bumblebee, but the workers seem to be more uniform in their duties. The stingless tropical bees of the genera Trigona and Melipona form very large communities, some of them even exceeding in size those of the honeybee, but the social life is practically the same. See BEE.

The wasps are also both social and solitary. The social species belong for the most part to the genera Vespa and Polistes. Their communities are much like those of the social bees. They are, however, not so perfect and not so persistent as those of the true honey-bee or the ants, but resemble more nearly those of the bumblebee. The communities of the bumblebees and the wasps are annual. Those of the honey-bee and the ants, as well as of the termites, last for a number of years. Among the wasps is a form known as worker, just as with the social bees, and the workers here, as in the other cases, are undeveloped females. Here also, as with the social bees, these undeveloped females or workers may lay eggs which invariably produce males or drones. Most of the social wasps make paper cells and nests, using for this purpose a wood-pulp composed of fragments of wood moistened with saliva, and macerated in the mouth. The economy of the social wasps is not perfectly understood, doubtless owing to the difficulty of studying them, due to the irritability of the insects and to their poisonous stinging. The size of the communities varies at the season when they are largest, from a few individuals to many hundreds, as many as 1200 cells being found in a single nest. On the approach of winter the males and workers perish

and the fertile females crawl into such protected situations as crevices of walls and in the bark of trees, and there pass the winter in the dormant state. At the opening of spring each surviving female founds a new colony. At first she performs the duties of both queen and worker. A small nest is made, eggs are laid in it, and when the larvæ hatch they are fed and cared for by the queen until they are mature. This first generation is composed entirely of workers. They relieve the queen of the duties which belong to them, and from this time forth her only duty is to lay eggs. The workers are engaged in the enlargement of the nest, in the construction of new cells, and in the care of the young.

With the ants we come to a more complicated social life. Here not only do great numbers of separate individuals live together and adopt different functions, according to the positions which they occupy in the colony, but these individuals are also greatly modified in structure, and in their physiological processes, in such ways as to fit them especially for the parts they have to play. With the different families of ants the character of the colony differs very considerably. For a general account of the community life of the higher families and the general phenomena of ant life, see ANT; also DRIVER ANT; FORAGING ANT, etc.

The family Poneridæ, as pointed out by Wheeler, constitutes a primitive and generalized group of ants, wherein the colonies consist of a comparatively small number of individuals like the incipient colonies of the higher families. These small colonies appear to be annual growths formed by swarming, as in bees, and not by single fertilized female ants, unaccompanied by workers, as in the higher families, and as described under ANT. Two and more colonies of the same species can be fused to form another colony without much difficulty, which is not easily accomplished with many species of the more specialized ants. Their architecture is of a primitive character, consisting of a few irregu lar and unfinished galleries. The queen and worker differ but little in size and structure. Ergatoid females, or forms intermediate between the queens and the workers, are of normal and comparatively frequent occurrence in some species. The habits of the queen and worker are very similar; the female is not an individual to whom especial attention is paid by the workers. The workers show no tendency to differentiate into major and minor castes. They are carnivorous and live by hunting, in contrast with the various harvesting, fungus-growing, honey-collecting, and aphid-guarding members of the higher groups. They do not feed one another by regur gitation; nor are the larvæ fed by regur gitation, but are given pieces of insects, from which they suck the juices. It is fair to suppose that from such generalized beginnings the highly specialized and wonderful colonies of the higher groups of ants have sprung, and that the slave-making habits, the care of honey-producing insects, the differentiation of a soldier caste, the fungus-growing habit, and others have been developed by gradual evolution.

The phenomenon of polymorphism (q.v.) becomes very marked with ants, although it reaches a still higher development among the termites. The causes of the modifications seen in the different castes are still in dispute. Dewitz states that

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