THE MOSQUITO
Here we have another small insect which, like the house fly, is
extremely dangerous, due to its ability to carry the germs of disease.
There are hundreds of species of mosquitoes, some small, some large. The
majority of these are unable to carry disease so far as we know at
present, but they should be avoided as dangerous. The Missouri forms
which carry disease are the so-called malarial fever mosquitoes, and
they are entirely responsible for the transmission of this sapping and
often fatal disease. In the warm countries these are more abundant and
the fever is more fatal. In the south there is still another
disease-carrying mosquito, the yellow fever mosquito. This form is most
dangerous of all.
The mosquito first bites a patient suffering with malaria and in this
way it takes in germs along with the blood which it sucks from the
patient. After these germs pass through stages of development in the
body of the mosquito they are ready to be injected back into a healthy
person where, in due time, they cause the disease. The germs feed inside
the red blood corpuscles and at regular intervals they destroy a large
number of these causing a chill which is followed by fever and a new
supply of corpuscles is produced. This alternation of chill and fever
may continue all summer, if medicine is not taken to destroy the germs.
Quinine will kill the germs if it is taken so that plenty of it is in
the blood when the germs come out of the torn down corpuscles during a
chill.
In order to prevent malarial fever, get rid of the mosquitoes by
draining and oiling the breeding places, escape their bites by screening
houses, smudging and destroying the adults, and keep the mosquitoes
from patients who have the fever. This is almost as important as the
destruction of the mosquitoes. The malarial fever mosquitoes are as
harmless as our common forms so long as they do not become infected with
germs by sucking blood from a fever patient.
[Illustration: Mosquitoes in position for biting; a, common Culex
mosquito; b, malarial fever mosquito. Note that the one stands parallel,
while the other stands at an angle to the surface on which it rests.]
In view of the fact that most of our common mosquitoes are classed as
non-dangerous, it is of interest to know just how to distinguish the
harmless ones from the dangerous. The adults of the two forms can be
easily distinguished when they are seen at rest. The common forms always
rest with the body parallel to the surface on which they rest, while the
malarial form always elevates the end of the body so that the head is
pointed toward the surface on which it rests. In like manner the
wigglers can be distinguished from each other. Our common wigglers
always hang head downward in the water while those of the malarial
mosquitoes rest near the surface of the water with their bodies parallel
to it. The majority of the wigglers found in rain barrels are of our
common forms.
[Illustration: Common Culex mosquito showing stages of development; a,
raft of eggs; b, larvae or wigglers of different sizes; c, pupa; d,
mosquito. The large wiggler and the pupa are taking air from the surface
of the water through their breathing tubes.]
The life of the mosquito is quite interesting and is an excellent
example of an insect which lives in the water part of its life and in
the air the rest. The mature female mosquito, which does all the
biting, searches for water in rain barrels, cans, ditches, ponds, and
stagnant swamps where she lays her eggs either in raft-shaped packets or
singly. When the wigglers hatch they swim about in the water and feed
upon decaying material and microscopic water plants. When the wiggler is
full grown it changes to an active pupa which has a large head and a
slender tail and is more or less coiled. A little later the winged
mosquito escapes. In the rural districts most of the mosquitoes breed in
stagnant ponds, swamps and rain barrels and from these they fly to the
home where they cause trouble. Such places should be drained or
protected with oil or other means to prevent the mosquito from using
them for breeding purposes. Ponds can be freed of the wigglers by
introducing fish or by using a small amount of coal oil on the surface.
The wigglers have a breathing tube which is thrust out above the water
when fresh air is needed and if there is a thin film of oil on the water
this is prevented. Rain barrels can be freed of the pest in this way
also, or perhaps better by covering them with a cloth. The mosquitoes
are most troublesome about the home at night. When one sits out doors he
should keep a smudge going to drive them away while screens will keep
them out of the house at night.
OBSERVATIONS AND STUDY
Collect all the different kinds of mosquitoes you can find and note
difference in size and markings. Do you find the malarial fever mosquito
in your region? Is malarial fever common during the summer and fall? Are
there any old stagnant ponds or swamps near your home? If so, examine
these for wigglers. Examine rain barrels for small raft-shaped packets
of eggs. These resemble small flakes of soot and are difficult to pick
up between your fingers. Take a stick and lift them from the water and
examine them. One packet may contain a hundred or more eggs. Put a few
of these packets in a tumbler of rain water and watch for the wigglers.
At first they will be very small but they grow fast. Watch them come to
the surface to breathe. The tip of the tail is projected above the water
and air is taken in at two small breathing pores or spiracles. Examine
rain barrels for the larger wigglers. What do they live on in the rain
barrel? What do they do when you jar the barrel? Do you find any of the
rounded pupae in the barrel? They are active the same as the wigglers.
If you find pupae, put some in a tumbler of water, cover it with cloth
or a lid and watch for the mosquitoes to appear. After collecting
several mosquitoes examine them for number of wings, legs and markings
and see if all have the slender sucking tube. The males have large
feathery feelers, but no sucking tube.
Write a brief description of the wiggler and the mosquito, their
breeding places and means of destroying them. Make drawings of the
different stages, wiggler, pupa and mosquito.