Pests

Pests, the name for animals that cause any harm to human health or to his economy, understanding the latter in the broadest sense. I. Pests of human health are: 1. Predatory animals whose victim may be a human; such, for example, are wolves, bears and other predators. Years of social disasters, wars, periods of decline in national well-being are accompanied by increased reproduction of wolves, which attack not only livestock but also humans; annually wolves tear apart more than a thousand people in our country. Mechanical injuries that can lead to death are also caused to humans by other animals, for example, wild boars (during hunting) and various domestic animals (bulls from the herd are particularly dangerous in this regard). In hot countries the number of pests that can become human prey is much greater (lions, tigers, crocodiles, sharks and many others).-2. Poisonous animals (see), producing poisonous substances that are normal products of their organisms. Animal poisons are either secreted by various (often specialized) glands (bee, scorpion, viper) or contained in various body tissues, for example, in blood (toxicity of eel blood, blood of Spanish fly), ovaries [poisonous principles of the ovary of various jawless fishes-tetradons). The ways in which toxicity manifests are different: some poisonous animals sting or prick humans (scorpions, wasps, caterpillars with poisonous hairs, fish with poisonous glands in the spiny rays of their fins); others-bite or prick with mouthparts [poisonous spiders, poisonous proboscis insects (Ari-lus, Harpactor and others), centipedes (scorpion), poisonous lizard Heloderma, snakes]; third lack any piercing organs and pour poison onto the surface of the body or onto human mucous membranes [insects-blister beetles-with the phenomenon of blood-sucking (autorrhagia), toads and others]; fourth poison humans when eaten (caviar of marinka fish-Schizothorax, caviar of tetradons and others). The practical significance of poisonous animals is determined by the frequency of their contact with humans and the nature of the action of their poison. As a rule, it can be considered that subtropical and tropical countries are particularly rich in poisonous animals dangerous to humans, as a result of which cases of snake poisoning are given a special column in sanitary statistics, filled in some me-Qcas-ECOL:.s!i энуэатодькьш» цэфраг-ЕГ. Ts.i:, in Brazil there are about 24,000 cases of people being bitten by poisonous snakes per year, of which about 4,800 people die. For India these figures are even greater (up to 20,000 deaths per year; although the statistics here are far from impeccable).-3. Parasites. Parasites (see) are animals that live at the expense of another organism, feeding either on its body tissues or on the food it digests. Various parasites also have humans as their hosts. The phenomenon of parasitism is widely spread in nature. Its significance is all the more aggravated for humans, as no organ of his body is insured against the possibility of settlement in it by this or that parasite. Parasites of humans are various protozoa (Protozoa), worms (Vermes) and arthropods (Arthro-poda). Depending on their location on the host, parasites are distinguished as external and internal (ecto- and endoparasites), and according to the duration of their stay on the host-as temporary parasites (bug) and permanent parasites (trichina). The phenomenon of 'carriage' is often observed also in relation to parasites; thus, not every person having microfilariae-M. nocturna [Wuchereria, (Filaria) Bancrofti] necessarily contracts elephantiasis; by no means every host infected with the broad tapeworm (Diphyllobothrium latum) contracts obvious malignant anemia, etc.; not all people are equally sensitive to bites and stings of various ectoparasites. Nevertheless, the total sum of harmfulness to humans from his parasites is very great. Parasites are the cause of various diseases, called, in contrast to infectious ones, invasion diseases (e.g., amebic dysentery, malaria, various types of helminth diseases, pediculosis, etc.). The nature of parasitic diseases is very diverse. In some cases, parasites cause various, atypical symptoms that do not make it possible to connect them etiologically with the presence in the human body of parasites that are often discovered only incidentally, e.g., diseases with various tapeworms, solitaire or with nematodes (roundworms, whipworms and others). In other cases, the symptom complex of an invasion disease is very typical (malaria, kala-azar, sleeping sickness, rishtha, bilharziasis and many others). The consequences of invasion diseases are different: a) reduced work capacity (malaria); b) delay in physical and mental development (ankylostomiasis in children); c) disability (e.g., loss of an eye when the solitaire larva or larvae of Wohlfart's fly develop in it, elephantiasis with enormous enlargement of some parts of the body-genitals, legs, breasts, etc.); d) chronic condition of the disease or its transition to a latent state with possible relapses (malaria) or prolonged disease in the presence of autoinvasion (pinworms, Hymenolepis diminuta); e) death either from the direct action of the parasite (e.g., in cerebral cysticercosis, malaria, kala-azar) or from possible complications (perforation of the intestine by tapeworms and their transition into the abdominal cavity, spontaneous rupture of the spleen from its excessive enlargement in malaria, etc.).-4. Carriers of pathogens of infectious and invasion diseases also occupy one of the first places among pests. The transfer of pathogens of various diseases can be first of all purely mechanical: the house fly, crawling on vomit or faeces of a cholera patient, gets contaminated with cholera bacteria, which it carries on its legs and proboscis. When flying to bread, sugar and other food, it contaminates them with bacteria and thereby creates conditions for human infection with cholera by eating contaminated food. Similarly, mechanical is the transfer of tabanids (Tabanidae) on their piercing mouthparts of various septic bacteria (anthrax and others). Such-contaminative and inoculative-transfers in the described cases are non-specific in the sense that the carrier is not an intermediate host of the transferred organism. The circle of specific carriers of protozoan and helminth parasites is much broader; such are, for example, Anopheles and the malarial plasmodium, mosquito and Leishmania tropica, mosquitoes and Bancroft's filaria, tick Ornithodorus and lice of the genus Pediculus and spirochetes of relapsing fever, etc. The significance of such specific carriers is all the greater that in their absence the corresponding disease cannot spread further.-5. Intermediate hosts of parasites and reservoirs of viruses are pests, since they serve as intermediaries and sources of infection of the environment around them with parasites, or second intermediate hosts, or humans themselves. For example, the cyclops is the intermediate host of rishtha, and a person becomes infected with it by swallowing with drinking water cyclops infected with the parasite. The same cyclops serves as the first intermediate host of the broad tapeworm, which infects the second host-fish, from which only does a person get this worm himself. Various mollusks (see) are intermediate hosts of one or another flukes. Such is the small pond snail (Limnaeus minutus) with respect to the liver fluke, Bullinus contortus and Schistosoma haematobium, Bythinia striatula and Clonorchis sinensis and others. In the absence of intermediate hosts, the parasite cannot complete its life cycle and perishes. An example of virus reservoirs can be various antelopes in Africa, in whose blood tryposomes parasitize that are harmless to them. When transferred through the agency of tsetse flies (Glossina) to humans, they cause sleeping sickness in them.- 6. Animals suffering from zoonoses, i.e., such diseases that are contagious to humans (actinomycosis, rabies, etc.)-7 Fish producing electricity due to possessing special electric organs, for example, electric eel (Gymnotus), electric ray (Torpedo) and others. II. Pests of human economy are: 1. Pests of health of domestic animals (in all respects existing also for humans, see above I, 1 - C) and wild animals of commercial value. Man suffers damage from: a) loss of livestock, b) its diseases (in babesiosis of cows lactation ceases, and animals often die), c) weakening of milk production (tick infestation of cows, attack of tabanids) and increase in live weight (in tick infestation), d) damage to organs used for technical purposes (holes in dressed leathers at the site of fistulas from larvae of skin gadflies of horned cattle) etc.- 2. Animals harmful to agricultural plants, shrubs and trees. Such pests are: a) of vegetable gardens (for example, the cabbage white butterfly, whose caterpillars devour cabbage leaves, and the Colorado potato beetle-pest of potatoes), b) of field crops (locusts), c) of beet plantations (beet weevil), d) of cotton plantations, e) of gardens (apple tree aphid), f) of vineyards (phylloxera), g) of forests (silkworm-monk, goldtail and many others). The economic significance of the damage caused by these pests is very great.

They can be the cause of crop failure with all the resulting consequences for the owner, up to famine. 3. Pests of food warehouses. These include warehouse pests (see) - various beetles, moths, and mites that live in warehouses and feed on grains and flour. In addition to the direct destruction of food supplies, warehouse pests can render the remnants of such supplies in warehouses unfit for food. Baked bread, crackers, salted fish, meat, and other products can also be affected by various insects and mites. For example, larvae of the cheese fly (Piophila casei) in salted fish and old cheese, larvae of various flies in meat, caterpillars of the pyralid moth (Aglossa pingui-nalis) - in fat, oil, lard, etc. 4. Pests of pharmacy warehouses. Some medicines (mostly of plant origin - roots, herbs, etc.) are attacked by certain beetles; the latter bore into them and spoil them. Even the poisonous Spanish fly (Lytta vesicatoria) is used as food by beetles Anobium paniceum, Anthrenus, Ptinus fur, Dermestes, etc., as well as mites Tyroglyphus, Glyciphagus, etc. 5. Pests of materials and leather. Caterpillars of the common clothes moth (Tineola biselliella) and the carpet moth (Tinea tapetiella) devour woolen materials and gnaw holes in them. The fur moth (Tinea pellionella) and the larder beetle (Dermestes lardarius) damage fur goods and leather products. 6. Pests of wood in handicrafts. Wooden furniture, as well as various structures, are attacked by various insects, mainly larvae and beetles (Anobium, Ptinus, Hylotrupes, etc.), termites, and rodents (rats and mice). Termites and rodents are universal pests, as they damage food supplies, materials, leather, books, linen, clothing, etc.