MOSQUITO BRIGADES THINGS TO BE LEARNT. 1. Leading Facts about Mosquitoes.-As everyone knows, mosquitoes invariably spring from larvæ which live in stagnant water on the ground or in vessels. But mosquitoes are of very many species, which often differ. in their habits. Full information on these points will be found in the literature, of which a list is added to this work. It is necessary to record here only a few leading facts. (1) Mosquitoes are the same as gnats. (2) All mosquitoes breed in stagnant water. * (3) The kind commonly known as Culex carry elephantiasis and yellow fever. They breed generally in vessels of water, cisterns, or drains. They bite sometimes in the day and sometimes at night, according to the species. When they are seated upon the wall their tails hang downwards. Their wings are rarely spotted. Their larvæ when undisturbed float on the surface of the water head downwards; when disturbed they wriggle immediately to the bottom of the vessel which contains them. * A vast number of species of gnats exist, and these species are grouped in a number of genera. Culex and Anopheles are the commonest genera in most places; but Culex has recently been divided into two genera, Culex and Stegomyia. The latter is the common brindled or tiger mosquito. It carries yellow fever, breeds mostly in vessels of water, and bites much in the daytime. For brevity, I use the word Culex in its old sense. (4) The mosquitoes known as Anopheles carry malarial fever. When they are seated on a wall their tails project at an angle outwards. Their larvæ are found mostly in shallow puddles on the ground, in small ponds, in slow and small runnels of water, in pools of rain-water on rocks, on the margin of slow-running streams, and sometimes, but rarely, in vessels of water. These larvæ float flat on the surface of the water like sticks, and move with a peculiar backward skating movement. The Anopheles bite mostly at night. (5) The larvæ of all kinds of gnats require at least six or seven days' life in water before they reach maturity and become winged insects. They cannot withstand thorough drying. Nor can the eggs. (6) Adult mosquitoes (that is, the winged insects) may live for months even in captivity. They hibernate in cold climates, and can resist severe frost or severe heat. They feed on fruit and leaves, on cattle and birds, as well as on men. As a rule it is only the females which feed on blood. (7) It is now a matter of the general experience of many investigators, that where mosquitoes abound in a house their larvæ can usually be found at a short distance, say within a few hundred yards from the house. Occasionally, where the house is isolated, and no stagnant water is in its immediate vicinity, mosquitoes may attack it from a greater distance; but this is exceptional, and in the great majority of cases, especially in towns, almost every house breeds its own mosquitoes in its backyards, or in puddles and drains in the streets close by. (8) Mosquitoes, especially Anopheles, love thick undergrowth. Further details will be found in the literature already mentioned; but most medical men at least will by this time be quite familiar with such facts. 2. Some Popular Misconceptions Corrected.—When the idea of exterminating mosquitoes for preventing malarial fever was first mooted* it was met with considerable opposition, and even ridicule, owing chiefly to various popular misconceptions regarding the matter. People thought that it was proposed to exterminate these insects in whole continents, which would evidently be quite impossible. As a matter of fact the measure was proposed only for towns and certain settlements. Then, again, by the phrase "extermination of mosquitoes " was never meant anything more than their reduction in numbers to an appreciable extent. Even as regards their reduction in number, serious doubts were felt at first, because it was believed that the insects exist in such countless swarms that all measures even to reduce them would be futile. a matter of fact, however, mosquitoes never exist in countless swarms. To make a rough estimate, I fancy it would be rare to find on the average more than twenty mosquitoes to every house, even in the most mosquito-infected districts. These insects, like other animals, have many natural enemies-bats, birds, spiders, and those climatic influences which tend to destroy them or their larvæ. It will indeed be contrary to general experience if these animals do not, as others have done, succumb when they find themselves opposed by a new enemy, and such a formidable one as mankind; that is to say, of course, in special localities where adequates measures are taken against them. As * In a letter addressed by me to the Government of India, dated February 18th, 1901. |