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The life and times
of the mosquito
‘The good Lord didn’t create anything without
a purpose, but mosquitoes come close.’
Mosquitoes – who needs them? Not like they play an
important role in the ecosystem as a whole. They aren’t a
major pollinator of flowers like other insects. They aren’t
even a major food source – except for a few bats and an
odd grayish fish (the Mosquito Fish) that specializes in
mosquito cuisine. And man are they a pain in the ass!
Swarms of them buzzing around your head, driving you
nuts. They are in your eyes, your ears, even your mouth.
They are nibbling at your ankles, the back of your knees.
Or maybe that single mozzie keeping you awake for hour
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after hour as it dive bombs you in your bed. Giving you
those itchy bites. Ruining the picnic, the view, the garden.
When the salt marsh mosquito (aedes taeniorhynchus)
swarms in the mangroves of the Florida Everglades in
June some claim they block out the sun. On the ‘mosquito
flyway’ that comes out of the Everglades and out over Key
Island on the Florida Gulf Coast the high-pitched hum
of their beating wings fills the air. A fancy resort (the
Keewaydin Club) stands deserted on the 2-mile long Key.
According to Gene Lemire of the local District authority:
‘We have mosquitoes so bad that in 1989, they were killing
cows. The cows were inhaling so many mosquitoes they
were choking, suffocating.’1 Further north there are even
stories in the Canadian northwoods about camp sites that
have been found with the bodies of campers completely
covered in feasting flies. But that’s all hearsay.
Bad neighbors
Mosquitoes (like humans?) are bad species neighbors.
For all the obvious reasons but also because mosquitoes
have a dirty little secret. They carry disease around with
them. Lots of disease: pathogens – the infectious agents,
such as bacteria or viruses. Often quite deadly or at least
debilitating. They take them from one horse to another.
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From one bird to another. From one monkey to another.
From one person to another. But they can also carry
them across species. Carrying them from individual-toindividual makes the mosquito a ‘vector’, from speciesto-species makes them a ‘bridge vector’. In this age of
global worry about pandemics of flu and runaway viruses
the old mozzie is taking center stage.
But we’d better get used to the mosquito because
they are a major evolutionary success story and despite
the efforts of humans, they aren’t going away any time
soon. Humankind (or at least those ‘representatives’
that get to decide for us) has brought the full weight of
industrial science to eradicate the pest and the results
have been partial at best. An arsenal of chemical and
pharmaceutical weaponry has been deployed. While
hundreds of thousands of lives have been saved by the use
of the chemical DDT and other measures, the 1950s and
1960s’ military language of eradication and liquidation
has proved wildly optimistic. The conquest of the winged
wonder is in a way a metaphor for the whole ‘domination
of nature’ and has had similar results. The mosquito, like
nature, continues to bite back.
With a bit of variation the life cycle of a mosquito such
as the common domestic mosquito of temperate climes
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LIFE-CYCLE
It’s pretty risky being a mosquito. Your mother ends up leaving
you in some stagnant water... a pond or clogged gutter.
You get left with a few hundred of your brothers and sisters
in an egg raft. Your egg may be destroyed before it even
hatches. Or you do get to hatch and reach the stage of being a
larva or even a pupa but there is just not enough to eat.
Then right away they are out to get you. Whether it is
mosquito fish wanting to make a meal of you or a scary water
strider trying to grab you. As you develop you become more
appetizing to birds, frogs, snakes and spiders.
Say you become a pupa. Your troubles have only started. Your
little mosquito body is starting to take shape and you need to
start breathing air. You develop two breathing tubes that you
stick above the water for some air. Now you are moving on to
the imago stage and you can leave your pupae cuticle behind.
If you are able to stay out of harm’s way until your cuticle splits
open things start to move along pretty dramatically. You lose the
ability to swim but you gain a set of wings and you can take off.
You’ve got half an hour to get out of the water and find a safe
refuge where your soft body can harden into a young mosquito.
This usually takes a day or two. Now you are ready to boogey!
But you certainly aren’t out of the metaphorical hot water.
There are still predators who want to vacuum you up including
that most deadly of mosquito serial killers: the bat. These guys
can grab you at night when you are flying along and think that
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you can’t even be seen. It’s almost as if they had radar.
Say you feel like a night out and decide as a young female
that you should head down to the swarm that the guys have
put together to attract you. They can tell it’s a girl by the
beating of your wings and, man, are they glad to see you!
You cut one out of the herd and before long there is a little
abdominal action and you are in the family way. Your eggs are
fertilized and you have some new needs. Not chocolate but a
bit of blood is what you crave.
You need to find a mammal to provide the blood for those
eggs. Here you have to be careful. Best to sneak in unnoticed,
and use your two stylets to break the surface of the skin. If you
can get your proboscis into a blood vessel you are home free. You
can use one tube of your proboscis to suck up the red stuff while
you stick some of your saliva from the other tube to prevent their
blood from clotting. This keeps the flow nice and steady and it’s
not really your concern what’s in the saliva you leave behind.
It takes about two minutes to fill up. You find a bit of surface
to settle on and let the food digest. But watch out! The nutrients
in a blood meal are attractive to predators. Does it never stop?
Then it’s off to find some stagnant water where you can
download those eggs. That’s a relief. Only problem is that when
you finish doing that your life is pretty much over. It’s all taken
about three weeks. Got to ask yourself – was it worth it? ◆
From Bobbie Kalman, The Life Cycle of a Mosquito (Crabtree
Publishing Company, 2004).
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– the Culex pipiens – is pretty much like that described
in the box. Some mosquitoes however can live for five or
six months. Some go into hibernation. Some species try
to guard their egg rafts. One type, the Anopheles salbaii,
an African desert dweller, doesn’t need a blood meal to
reproduce.
The eggs of some can survive in desert or arctic
conditions for very long periods, in the case of one Sahara
mosquito through decades of drought before a rainfall
finally completes fertilization. And some (the most
dangerous) mosquitoes take a blood meal more than
once. Others are very particular where they take their
blood from, such as a Canadian type which will bite only
Loons (not mad people, but the Canadian national bird,
an aquatic fowl). Yet others will bite across species and
pass on infection say from monkeys or birds to people.
Remember, the older the mosquito, the more likely they
have some kind of nasty surprise with their bite.
Champion of adaptation
Given the precariousness of their lives it seems a wonder
the mosquito is still with us. After all, almost 50 per
cent never make it through their first day. But the pesky
critters are evolutionary survivors par excellence. They
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MOSQUITO DEFINED
In English, the word Mosquito (Spanish, little fly) dates back to
1583; the word was adopted to replace the term ‘biting flies’ to
prevent confusion with the house fly. It is derived from the word
musca and is related to the Italian moschetta and the French
moustique. Mosquitoes are arthropods, an insect classification
which constitutes over 90 per cent of the animal kingdom.
Why do they bite?
Mosquitoes belong to a group of insects that require blood
to develop fertile eggs. Males do not lay eggs, thus, male
mosquitoes do not bite. The females are the egg producers
and ‘host-seek’ for a blood meal.
Both male and female feed on plant nectar, fruit juices
and liquids that ooze from plants. The sugar is burned as
fuel for flight. Blood is reserved for egg production and is
imbibed less frequently.
Why are some people more attractive to mosquitoes
then others?
Scientists are still investigating the complexities involved with
mosquito host acceptance and rejection. Some people are
highly attractive and others are rarely bothered. Mosquitoes
have specific requirements to satisfy and process many
different factors before they feed. ◆
Wikipedia http://en.wikipedia.org
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have been around since the time of the dinosaurs and
witnessed a lot of other species come and go. They survive,
indeed prosper, from Himalayan mountain slopes up
to 11,000 feet to below sea level in Baja California. The
aggressive Aedes communis swarms north of the Arctic
Circle literally eating the poor caribou alive. While down
in Eritrea’s Danakil Depression, one of the hottest places
on earth, the mosquito has also learned to get by. So hot
or cold, high or low, dry or wet (although wet is preferable)
mozzies find a way.
The mosquito is a member of the family Culicidae.
Altogether there are between 2,500 and 3,000 different
types of mosquito with an estimated global population of
100 trillion (although God knows how anyone can really
tell). They are also implicated as the greatest killers of
humans. Between one and three million die of malaria
alone every year and this says nothing about a range of
other mosquito-borne diseases – West Nile virus, yellow
fever, dengue, and various forms of encephalitis. The
mosquito bite itself, while certainly annoying, is not what
spreads the disease. But certain types of mosquitoes act
as what are called ‘disease vectors’ carrying ‘pathogens’
(infectious agents) including viruses they pick up from
one mammal to infect another.
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Mozzie types
There are three main genus of mosquito – Anopheles, the
Culex and the Aedes. The main culprit in the transmission
of malaria is Anopheles, a type of warm weather mosquito.
Of the 400 or so mosquito species of genus Anopheles
about 60 transmit the plasmodium parasites that cause
malaria. Species in the Anopheles gambaie are the main
spreaders of malaria in Africa where the human toll
amongst children results in about 90 per cent of malaria
cases and deaths.
The Culex is the most common mosquito in the Northern
hemisphere and the least likely to carry dangerous
pathogens although it can carry viral encephalitis and
filariasis (also known as elephantiasis) in tropical and subtropical regions. Recently it was discovered that certain
types of the Culex are also a vector for West Nile virus.
The genus Aedes during its short life span can carry
yellow fever, dengue and also encephalitis. Some of the
Aedes are known as ‘house mosquitoes’ because of their
tendency to breed in domestic locales in rain/water
barrels, birdbaths, buckets and so on. Their short life
and local range make it possible to cut down on their
population by eliminating all domestic breeding habitats.
This is one of the ways health authorities have been able to
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get on top of the peril of yellow fever. Other Aedes are the
salt marsh variety known for their fierce swarming that
can drive various mammals (including us) almost mad
with the desire to escape. They are more easily subjected
to aerial spraying because of their location and tendency
towards large-scale swarming.
Mosquito-borne diseases
It was only in the last couple of decades of the 19th century
that suspicions were finally confirmed that mosquitoes were
a major carrier of a number of dangerous diseases. While
this ended centuries of blind panic in the face of mysterious
epidemics and plagues, it started a mortal combat between
people and the winged tormentors. The outcome is still
undecided. The following are the main diseases that we now
recognize are spread by mosquito bite.
Malaria
Malaria, derived from mal aria (Italian for ‘bad air’) and
formerly called ‘ague’ or ‘marsh fever’ in English, was
originally thought to be produced by ‘miasma’ or poisoned
air. According to the World Health Organization, more
than 3 billion people (roughly half the world’s population)
live under the threat of malaria. Each year, the disease
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causes about 350-500 million infections in humans and
kills about 1.3 million – mostly children. It remains the
deadliest disease for which the mosquito acts as a vector.
It is the most common of tropical diseases, killing mainly
the already weakened or vulnerable (by disease, age or
malnutrition) or the very young who have no immunity
built up. Sub-Saharan Africa is home to some 90 per cent
of the world’s malaria cases and deaths.
Once inside the body the malaria parasite multiplies in
the liver and red blood cells. Severe cases suffer alternately
from frigid chills that can lead to violent shakes, and bouts
of high fever that can reach 106o Fahrenheit. The victim’s
red blood cells are made sticky by the parasite clogging
their vascular system and starving the brain and other vital
organs of oxygen. For the dying the sequence is lethargy,
delirium and finally coma. Some historians estimate that
during the Second World War US forces in the Pacific lost
more troops to malaria than to the Japanese.
Yellow fever
This causes fever, jaundice and hemorrhages that
eventually kill a great number of those who contract
it. Yellow fever (or Yellow Jack as it used to be called)
can result in the most terrible of deaths involving
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MOSQUITOES – THE NUMBERS
The average female mosquito’s wings beat between 250 to 500
times a second.
A mosquito can hit a top speed of about 3 miles an hour.
Mosquitoes fly about 150 miles in their lifetime.
Most mosquitoes live within one mile of where they have been
hatched. A few species can range up to 20 miles.
A female mosquito usually lives from 3 to 100 days. A male from
10 to 20 days.
A female may lay 1,000 to 3,000 eggs over the course of its
lifetime.
Biting activity can increase up to 500 times with a full moon.
The female mosquito can suck up to three times its body weight
in blood.
20 per cent of people receive 80 per cent of bites from infected
mosquitoes.
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MALARIA – THE NUMBERS
There are between 300,000 and 500,000 new cases of clinical
malaria every year.
The global death toll from malaria and malaria-related diseases
is over 1 million people each year.
Depending where they live, people in Africa can receive
anywhere between one to 1,000 infective mosquito bites per
year. By contrast the average in Latin America or Southeast Asia
is one infective bite most years.
Africa is home to around 90 per cent of the world’s malaria cases
and related deaths. In Kenya 11 per cent of schooldays are lost
every year because of the disease.
Children (mostly African) can have as many as 5 different strains
of malaria in them at once.
The disease costs Africa between $3 and $12 billion a year but
could be controlled for much less. ◆
www.mosquitozapper.com/facts; ‘Combating Malaria’, Anne
Platt McGinn, State of the World’s Children Report 2003, UNICEF.
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uncontrollable bleeding and vomiting. In the past, it was
feared for its intensity and the rapidity with which it
spread. The so-called ‘ghost ships’ like the famous Flying
Dutchman found abandoned, floating lifeless in the
ocean, were probably a consequence of yellow fever.
In her book Yellow Fever and the South, Margaret
Holmes quotes a letter from a man who watched his
daughter die: ‘Jaundice was marked, the skin being a
bright yellow hue; tongue and lips dark, cracked and
blood oozing from the mouth and nose... to me the most
terrifying feature was the black vomit which I never
before witnessed. By Tuesday it was black as ink and
would be ejected with terrific force.’2 The yellow fever
virus can still be found in wild primates in Africa and
the Americas. It is much less of a threat than it used to
be (there are effective vaccines for those who can afford
them); however it remains a problem particularly in
relatively remote jungle areas.
Dengue
Dengue is known as ‘break-bone fever’ because of the acute
skeletal pain associated with the disease. There are four
distinct types of dengue fever (DF), but only one dengue
hemorrhagic fever (DHF – a combination of two types of
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dengue) is likely to be fatal. The disease occurs at various
spots throughout the Global South. In 1970 dengue was
found in nine countries, while today it is in 60. As with
yellow fever, dengue is spread by Aedes aegypti. By 2005
the disease had a global distribution comparable to that
of malaria with an estimated 2.5 billion people living in
risk areas. Each year, tens of millions of cases of DF occur
and depending on the year up to hundreds of thousands
of cases of DHF. The case-fatality rate of DHF in most
countries is about five per cent. But with proper treatment
this could be reduced to below one per cent. It is mostly
the young who die.
Encephalitis
This is caused by the encephalitis virus, an ‘arbovirus’.
Arbovirus is short for arthropod-borne virus. There
are several types, including the St Louis (SLE), Western
Equine (WEE) and Eastern Equine (EEE) encephalitis.
The last two are viral diseases transmitted to horses
and humans by mosquitoes; but the virus that causes
EEE cannot be passed from horses to humans. Once
contracted, the virus can result in an inflammation of the
brain and the membrane that surrounds it. This can lead
to mild outcomes such as flu-like symptoms, but can be
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MOSQUITO
....crawling into my head, mosquito, mosquito red pieces,
diseases, floating in the greases, but they smile instead
sting of the suckerfly
in the dead of the night
ride on the wings of a dragonfly
sleep by the candlelight
sucking the gutter dry
taking flight
now they dance on the open eye
pushing the needle to the tiny bite
watching the circling sun, mosquito, mosquito run
vision of a killing gun
they sing with the voices of the angels son
river is flowing
the bloody wind is blowing
the reaper they are sowing
and i don’t believe that they are going
crawling into my eye, mosquito, mosquito fly
falling from the scientist slide
eating at the walls from behind they hide...
Psychotic Waltz, US progressive metal band
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lethal in some cases. EEE is the most serious with older
victims dying of their infection while the young enter
a semi-comatose state that gives EEE its more popular
designation as ‘sleeping sickness’. EEE often has ‘swamp
mosquitoes’ (Culiseta melanura) as its main vector. These
are particularly active in wet conditions and feed mostly
on birds that become the reservoir of EEE. The birds are
then bitten by other mozzies that also bite humans. Such
mosquitoes are known as ‘bridge vectors’ as they transfer
pathogens from one species to another.
West Nile virus
This affects mainly birds but can be found in a number of
mammals including humans and horses. It is transmitted
by varieties of the Culex mosquito and was first discovered
in Uganda just before the Second World War. It has almost
no effect on 80 per cent of the people who contract it but
does cause a mild fever in a minority. An even smaller
minority of mostly older victims get quite sick with
symptoms of fever, nausea and even paralysis. Death
occurs in a small minority of cases. No effective treatment
is known. The geographic spread of West Nile virus has
increased dramatically because of the migratory habits
of bird hosts and the very common mosquito vectors that
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also act as bridge vectors between birds and mammals. In
1999, after a few fatal cases in New York City, the mayor
had the whole city doused with insecticide.
Filariasis
This is spread by the filaria worm. It can cause extreme
disfigurement and is commonly known as elephantiasis.
This is one of the diseases with the highest level of social
stigma attached to it (like leprosy) because of the dramatic
disfigurements that frequently accompany it: everything
from genitals to limbs can be swollen almost out of
recognition. Although the disease is seldom fatal, secondary
infections following surgical intervention may cause death.
It was with filariasis that a British doctor, Patrick Manson,
first suggested a link to the mosquito. Manson worked in
Taiwan in the 1870s where he saw hundreds of cases and did
initial research that identified the mosquito as the vector
bearing the filaria worm. Today full-blown elephantiasis
is rare due to overall improvements in health, mosquito
control programs and the use of the drug Ivermectin to
control infection before it gets out of hand.
Another type of filarial infection which also occurs in the
tropics is ‘river blindness’ (Onchocerciasis) that literally
renders those affected sightless if not properly treated.
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