Gateway to the Classics: Handbook of Nature Study: Insects by Anna Botsford Comstock
 
Handbook of Nature Study: Insects by  Anna Botsford Comstock

The Mosquito

Teacher's Story

dropcap image N DEFIANCE of the adage, the mother of our most common mosquitoes does not hesitate to put her eggs all in one basket, but perhaps she knows it is about the safest little basket for eggs in this world of uncertainties. If it were possible to begin this lesson with the little boat-shaped egg baskets, I should advise it. They may be found in almost any rain barrel, and the eggs look like a lot of tiny cartridges set side by side, points up, and lashed or glued together, so there shall be no spilling. Like a certain famous soap, they "float," coming up as dry as varnished corks when water is poured upon them.


[Illustration]

The egg-raft of a mosquito, enlarged.

The young mosquito, or wriggler, breaks through the shell of the lower end of the egg and passes down into the water, and from the first, it is a most interesting creature to view through a hand lens. The head and the thorax are rather large while the body is tapering and armed with bunches of hairs. At the rear of the body are two tubes very different in shape; one is long, straight and unadorned; this is the breathing tube through which air passes to the tracheæ of the body. This tube has a star-shaped valve at the tip, which can be opened and shut; when it is opened at the surface of the water, it keeps the little creature afloat and meanwhile allows air to pass into the body. When the wriggler is thus hanging at an angle of 45 degrees to the surface of the water, it feeds upon small particles of decaying vegetation; it has a remarkable pair of jaws which are armed with brushes, which in our common species, by moving rapidly, set up currents and bring the food to the mouth. This process can be seen plainly with a lens. When disturbed, the wriggler shuts the valve to its breathing tube, and sinks. However, it is not much heavier than the water; I have often seen one rise for some distance without apparent effort. The other tube at the end of the body, supports the swimming organs, which consist of four finger-like processes and various bunches of hairs. When swimming, the wriggler goes tail first, the swimming organs seeming to take hold of the water and to pull the creature backward, in a series of spasmodic jerks; in fact, the insect seems simply to "throw somersaults," like an acrobat. I have often observed wrigglers standing on their heads in the bottom of the aquarium, with their jaws bent under, revolving their brushes briskly; but they never remain very long below the surface, as it is necessary for them to take in fresh air often.


[Illustration]

A mosquito aquarium.

The pupa has the head and thoracic segments much enlarged, making it all "head and shoulders" with a quite insignificant body attached. Upon the thorax are two breathing tubes, which look like two ears, and therefore when the pupa rests at the surface of the water, it remains head up so that these tubes may take in the air; at the end of the body are two swimming organs which are little, leaf-like projections. At this stage the insect is getting ready to live its life in the air, and for this reason probably, the pupa rests for long periods at the surface of the water and does not swim about much, unless disturbed. However, it is a very strange habit for a pupa to move about at all. In the case of other flies, butterflies, and moths, the pupa stage is quiet.


[Illustration]

A wriggler or larva of mosquito (culex), greatly enlarged.

Drawn by Evelyn Mitchell.

When fully mature, the pupa rises to the surface of the water, the skeleton skin breaks open down its back and the mosquito carefully works itself out, until its wings are free and dry, meanwhile resting upon the floating pupa skin. This is indeed a frail bark, and if the slightest breeze ruffles the water, the insect is likely to drown before its wings are hard enough for flight.

The reason that kerosene oil, put upon the surface of the water where mosquitoes breed, kills the insects is because both the larvæ and pupæ of mosquitoes are obliged to rise to the surface, and push their breathing tubes through the surface film so that they will open to the air; a coating of oil on the water prevents this, and they are suffocated. Also when the mosquito emerges from the pupa skin, if it is even touched by the oil, it is unable to fly and soon dies.

The male mosquitoes have bushy, or feathery, antennæ. These antennæ are hearing organs of very remarkable construction; (see Ways of the Six-Footed, p. 8.) The Anopheles may be distinguished from the Culex by the following characteristics: Its wings are spotted instead of plain. When at rest it is perfectly straight, and is likely to have the hind legs in the air. It may also rest at an angle to the surface to which it clings. The Culex is not spotted on the wings and is likely to be humped up when at rest. In our climate the Anopheles is more dangerous than the Culex because it carries the germs of malaria. A mosquito's wing under a microscope is a most beautiful object, as it is "trimmed" with ornamental scales about the edges and along the veins. The male mosquitoes neither sing nor bite; the song of the female mosquito is supposed to be made by the rapid vibration of the wings, and her musical performances are for the purpose of attracting her mate, as it has been shown that he can hear through his antennæ a range of notes covering the middle and next higher octaves of the piano.


[Illustration]

Antenna of male mosquito, enlarged.

Of late we are learning that the mosquitoes are in a very strange way a menace to health. Through a heroism, as great as ever shown on field of battle, men have imperiled their lives to prove that the germs of the terrible yellow fever were transmitted by the biting mosquito, and with almost equal bravery other men have demonstrated that the germs of malaria are also thus carried.


[Illustration]

The pupa of a mosquito, greatly magnified. Note  b the breathing tubes near the head.

Drawn by Evelyn Mitchell.

In the North, our greatest danger is from the mosquitoes which carry the malarial germs, and these are the mosquitoes with spotted wings and belong to the genus Anopheles. This mosquito, in order to be of danger to us, must first feed upon the blood of some person suffering from malaria (ague) and thus take the germ of the disease into its stomach. Here the germ develops and multiplies into many minute germs, which pass through another stage and finally get into the blood of the mosquito and accumulate in the salivary glands. The reason any mosquito bite or insect bite swells and itches is because, as the insect's beak is inserted into the flesh, it carries with it some of the saliva from the insect's mouth. In the case of Anopheles these malarial germs are carried with the saliva into the blood of the victim. It has been proven that in the most malarial countries, like Italy and India, people are entirely free from malaria if they are not bitten by mosquitoes.

After this explanation has been made, it would be well for the teacher to take the pupils on a tour of inspection through the neighborhood to see if there are any mosquito larvæ in rain barrels, ponds or pools of stagnant water. If such places are found, let the pupils themselves apply the following remedies:

1. Rain barrels should be securely covered.

2. All stagnant pools should be drained and filled up if possible.

3. Wherever there are ponds or pools where mosquitoes breed that cannot be filled or drained, the surface of the water should be covered with a spray of kerosene oil. This may be applied with a spray pump or from a watering can.

4. If it is impracticable to cover such places with oil, introduce into such pools the following fish: Minnows, sticklebacks, sunfish and goldfish.

The effect of this lesson upon the children should be to impress them with the danger to life and health from mosquitoes and to implant in them a determination to rid the premises about their homes of these pests.


References—Farmers' Bulletin No. 155, U. S. Department of Agriculture, by L. O. Howard; leaflet in Reading Course for Farmers' Wives, series 2, No. 10, by M. V. Slingerland; American Insects, Kellogg; The Insect Book, Howard; Insect Life, The Manual for the Study of Insects, Comstock; Ways of the Six-Footed, Comstock.


[Illustration]

Wing of mosquito, enlarged.

Comstock's Manual.

Lesson XC

The Mosquito

Leading thought—The wrigglers, or wigglers, which we find in rain-barrels and stagnant water are the larvæ of mosquitoes. We should study their life history carefully if we would know how to get rid of mosquitoes.


Method—There is no better way to interest the pupils in mosquitoes than to place in an aquarium jar in the schoolroom a family of wrigglers from some pond or rain barrel. For the pupils' personal observation, take some of the wrigglers from the aquarium with a pipette and place them in a homeopathic vial; fill the vial three-fourths full of water and cork it. Pass it around with a hand lens and give each pupil the opportunity to observe it for five or ten minutes. It would be well if this vial could be left on each desk for an hour or so during study periods, so that the observations may be made casually and leisurely. While the pupils are studying the wrigglers, the following questions should be placed upon the blackboard, and each pupil should make notes which may finally be given at a lesson period. This is particularly available work for September.

In studying the adult mosquito, a lens or microscope is necessary. But it is of great importance that the pupils be taught to discriminate between the comparatively harmless species of Culex and the dangerous Anopheles and therefore they should be taught to be observant of the way mosquitoes rest upon the walls, and whether they have mottled or clear wings.


The Larva

Observations:

1. Note if all the wrigglers are of the same general shape, or if some of them have a very large head; these latter are the pupæ and the former are the larvæ. We will study the larvæ first. Where do they rest when undisturbed? Do they rest head up or down? Is there any part of their body that comes to the surface of the water?

2. When disturbed what do they do? When they swim, do they go head or tail first? When they float do they go upward or downward?

3. Observe one resting at the top. At what angle does it hold itself to the surface of the water? Observe its head. Can you see the jaw brushes revolving rapidly? What is the purpose of this? Describe its eyes. Can you see its antennæ?

4. Note the two peculiar tubes at the end of the body and see if you can make out their use.

5. Note especially the tube that is thrust up to the surface of the water when the creatures are resting. Can you see how the opening of this tube helps to keep the wriggler afloat? What do you think is the purpose of this tube? Why does it not become filled with water when the wriggler is swimming? Can you see the two air vessels, or tracheæ, extending from this tube along the back the whole length of the body?

6. Note the peculiarities of the other tube at the rear end of the body. Do you think the little finger-like projections are an aid in swimming? How many are there?

7. Can you see the long hairs along the side of the body?

8. Does the mosquito rest at the bottom of the bottle or aquarium?


The Pupa

9. What is the most noticeable difference in appearance between the larva and pupa?

10. When the pupa rests at the surface of the water, is it the same end up as the wriggler?

11. Note on the "head" of the pupa two little tubes extending up like ears. These are the breathing tubes. Note if these open to the air when the pupa rests at the surface of the water.

12. Can you see the swimming organs at the rear of the body of the pupa? Does the pupa spend a longer time resting at the surface than the larva? How does it act differently from the pupæ of other flies and moths and butterflies?

13. How does the mosquito emerge from the pupa skin? Why does kerosene oil poured on the surface of the water kill mosquitoes?


The Adult Mosquito

1. Has the mosquito feathery antennæ extending out in front? If so, what kind of mosquitoes are such?

2. Do the mosquitoes with bushy antennæ bite? Do they sing?

3. Are the wings of the mosquito spotted or plain? How many has it?

4. When at rest, is it shortened and humpbacked or does it stand straight out with perhaps its hind legs in the air?

5. What are the characteristics by which you can tell the dangerous Anopheles?

6. Why is the Anopheles more dangerous than the Culex?

7. Examine a mosquito's wing under a microscope and describe it.

8. Examine the antennæ of a male and a female mosquito under a microscope, and describe the difference.

9. Which sex of the mosquito does the biting and the singing?

10. How is the singing done?


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