In five or six days the larvae change into pupae. In about two days more these assume the form of the ordinary adult mosquito. Hence in hot weather a generation of mosquitoes develops in from eight to ten days. Consider ing the number of eggs laid by a sin gle female it will be readily seen that countless millions of these pests may breed in a single pool, pond, or swamp during one summer season.
To Destroy Mosquitoes. — Happily, the experiments of scientific observers seem to indicate that mosquitoes do not usually fly very far from the pools in which they were hatched. They re quire as breeding places pools of stag nant water that remain undisturbed for from ten days to two weeks, and they may be completely destroyed by covering the surface of these pools with a thin film of petroleum or kero sene oil. Hence the problem of ex terminating mosquitoes is strictly a local one, and the means are quite within the reach of every responsible person. Farmhouses are often far apart, so that all the mosquitoes about the house and farm buildings are bred on the place. Consequently, the re sponsibility for exterminating them is purely an individual one.
Or a group of neighboring farmers can often be persuaded to act in har mony, or at least to permit an enter prising neighbor to take measures to prevent the breeding of mosquitoes in their vicinity.
School children may be encouraged to undertake the extermination of mosquitoes in an entire school dis trict, or boards of health may be per suaded to take up the problem and appoint voluntary or paid representa tives to wage a war of extermination through the entire community.
Kerosene for Mosquitoes.—To de stroy mosquitoes, apply petroleum or kerosene oil to the surface of the pools, puddles, or marshes in which they breed. One ounce of kerosene is sufficient for 15 square feet of stag nant water. Thus a tank or pool 10 feet across would require about 1i pints of the oil.
To apply the oil on small puddles, tanks, or pools, it is only necessary to pour it on the surface or scatter it to windward with a wide sweep of the arm. The oil will spread itself over the surface in a uniform film. But for larger ponds, marshes, and pools overgrown about the edges with grass or weeds which may prevent the oil from penetrating to every part, it is better to use an ordinary sprayer hav ing a fine nozzle, such as is used for spraying fruit trees with Bordeaux mixture. This may be applied in pools
by wading or from a raft or boat.
A single application of oil kills all eggs laid upon the surface and all wigglers previously hatched. The film of oil prevents their coming to the surface to breathe, hence they are suf focated or " drowned." The oil does not prevent the female mosquito from attempting to deposit her eggs on the surface, but destroys her in the act of doing so; consequently, until the oil evaporates, the breeding of mos quitoes is totally prevented. The film of oil, if undisturbed, will not evapo rate for a week or more, and at least ten days will be required after it has evaporated for a generation of mos quitoes to mature. Hence in absolute ly still water where there is no current to carry off the oil, two applications month will be quite sufficient. In covered tanks, drains, and cesspools not exposed to the sun, one application month should be enough. But those who are fighting mosquitoes must re member that after a rain an old tin can, the print of a cow's foot in the mud, or a puddle left in a wagon rut or hollow may breed enormous num bers of mosquitoes if it remains un disturbed for a period of ten days or more. Hence a few days after a rain the ubiquitous small boy should be sent abroad with a small wat-erpot having a fine nozzle and containing a gallon or more of kerosene, and he should be instructed to cover the sur face of these pools with a layer of the oil. Tin cans before being thrown on the dump should have the bottoms knocked out or a few holes punched in them with a can opener. An ounce of prevention is better than a pound of cure.
To Destroy Mosquitoes by Drain age.—This needs little comment. Ob viously, if swamps, pools, and the like have tile or other drains laid beneath their surface so that the water is en tirely drawn off, mosquitoes cannot breed in them. But open drains are themselves favorite breeding places of mosquitoes. Hence these should be spread with oil, especially along the edges where grass and weeds make the current sluggish. If there is much current, they should be sprayed two or three times a month.