The Mosquito—Insect Menace of the Night?
THE shades of night have fallen and darkness prevails. You have retired early, hoping to enjoy hours of peaceful slumber. But a familiar whine breaks the stillness of the warm, balmy evening. Your bedroom has been invaded! Tense, worried, fearing the worst, you wait. You feel nothing and think the danger is past. But too late you realize that you have become a victim. Incessant itching reveals that you have not escaped the sting of what you might be inclined to dub ‘the insect menace of the night’—the mosquito.
From now till the end of summer, you are determined that any opened windows will be screened. In fact, you may use oils and sprays on exposed parts of your body—all in an effort to discourage assault by the menacing mosquito. Of course, you are not the first to wage such warfare. It is said that the Egyptians were using smudge pots and mosquito nets for the same reason some thirty centuries ago.
Yet, your best defense may be a better knowledge of this foe. What are mosquitoes really like? Why do they “bite” people? Do these insects serve any useful purpose?
From Egg to Adult
Mosquitoes are insects of the order Diptera, meaning “two-winged.” There are over 2,500 species and they certainly are widespread. You can find them breeding in hot tropical pools or cold Arctic waters!
Mosquitoes go through four stages: (1) egg, (2) larva, (3) pupa, and (4) adult. Through the ovipositor in the abdomen, the female may lay some 100 to 300 eggs on a single occasion. Certain species form eggs into a raft of sorts, held together by a substance the female emits. The eggs may be laid in a marsh or even a little pool in a ditch or a hollow log. Hatching may occur in two or three days, except for species like the pond mosquito. Some of its eggs, deposited in a dried-up pond, do not hatch until they have been soaked three times. Otherwise, they might hatch during a brief wet period and the larvae would perish when the pond became dry again. Floodwater mosquitoes lay eggs in mud resulting from a flood, and these do not hatch until another flood has occurred, possibly after years have passed.
Frequently called the wriggler for its movements through the water, the larva of the mosquito is wormlike in appearance. Around its mouth are tiny hairs that sweep in food—minute plants, single-celled creatures called protozoans, and even other wrigglers. To breathe, some mosquito larvae push a sort of snorkel or air tube above the water. In one swampland species, however, the air tube is pointed and the larva jabs it into a cattail, sedge or other plant to obtain oxygen. Many mosquito larvae molt, or shed their skins, four times in some four to ten days.
After the final molt, the creature becomes a pupa. It breathes through tubes on its thorax that are sent above the water’s surface. In certain species, these tubes are used to obtain oxygen from underwater plants. Because of the way the pupae of most mosquito species roll about, they are called tumblers. They eat nothing and undergo quite a change in a few days.
Emerging from the pupal shell is the adult mosquito. It begins flying after its wings dry. Mr. Mosquito may live only ten to twenty days and his ‘lady friend’ a month or more. Of course, life-spans vary according to species. Some female mosquitoes may survive the winter in your garage or barn.
“Boy” Meets “Girl”
Mr. Mosquito pays no attention to his female counterpart during the first day or two of his adult life. It takes that long for the tiny hairs on his antennae to dry out, enabling him to hear. But then just let the ‘young lady’ fly by! The whine of her wings strikes his “feelers,” and impulses are sent to his brain. In mosquito jargon, the message must be “It’s a girl!” Quickly, Mr. Mosquito seizes the female and mates with her.
New Zealand’s Opifex mosquito can hardly wait to mate. Males continue flying over breeding waters just waiting for pupae to come to the surface! The eager males actually mate with the females before they manage to get out of the newly opened pupal shell.
A Physical Check-up
An adult mosquito’s body is made up of the head, thorax and abdomen. On the head are two compound eyes with thousands of lenses, each eye able to function independently. Between the eyes are two antennae, with which the insect hears and smells.
The menacing part of mosquito anatomy is a funnel-shaped mouth. Wide at the head, it narrows into a tubular proboscis. Incidentally, only Mrs. Mosquito can “bite” you. The “boys” of the “family” are not equipped to cause such torture. But, more about that later.
A short neck joins the head to the thorax. To it are attached the insect’s three pairs of legs, as well as two wings through which blood-carrying veins show clearly. Scales, sometimes quite colorful, cover the wing edges and the veins. The whine you hear when a mosquito nears is the sound of its wings in motion. Rodlike parts (halteres) behind the wings enable the insect to maintain balance. During flight, they vibrate at the same rate as the wings. Also, by developing harmonious vibrations in the air and its thorax, the mosquito is said to get “more flaps out of its wings than its nerves or muscles could sustain alone.”
In the mosquito’s long tubelike abdomen are situated the stomach and the intestines. The insect breathes through small holes called spiracles. There are eight pairs of these in the abdomen and two pairs in the thorax.
The mosquito’s body is covered by an elastic shell. And these troublesome insects come in an assortment of colors. Most of them are black, brown, tan or gray, but some are green or blue. Markings in white or light colors appear on the backs, wings or legs of a good many species, though it is unlikely that you will be admiring their decorations when under assault.
Are All Mosquitoes Disease Carriers?
That question may well be asked, since most people have heard that these insects transmit various diseases. When there was an outbreak of yellow fever in New Orleans, Louisiana, the “culprit” turned out to be a type of mosquito that seemingly preferred to lay its eggs in a flower vase. Why, these insects were breeding in the water of flower vases that had been placed on the graves of yellow-fever victims!
Back in 1878, it was found that the Culex quinquefasciatus mosquito transmitted filariasis, a malady causing glands and limbs to swell and sometimes resulting in elephantiasis. Within another nine years certain kinds of Anopheles mosquitoes were identified as carriers of malaria. By 1900 it was known that yellow fever was carried by the Aëdes aegypti.
Certain mosquitoes do carry over a dozen human maladies. Actually, however, very few species are disease carriers. So you do not necessarily have that to worry about when attacked by this insect. Nevertheless, you may be wondering why these creatures pick on you in the first place. In fact, it might be asked:
Why Are You So Attractive?
Researchers have concluded that bodily warmth and the moisture of human skin are factors that attract mosquitoes. They may also be drawn by lactic acid in an individual’s perspiration and breath, as well as by the carbon dioxide exhaled by animals and people. In fact, the amino acids and hormones in the human body’s fluids may draw mosquitoes. There is nothing you can do about any of these things, unless you stop breathing.
Women may draw a little comfort from the fact that Mrs. Mosquito usually finds men more attractive. For that matter, these insects customarily assault the most “attractive” individual in a group. So, you may escape while an associate is virtually being “devoured.” Of course, this attractiveness has nothing to do with beauty or good looks. But, then, how could anyone be disappointed about not appealing to menacing mosquitoes?
How Mrs. Mosquito “Bites”
Since you probably have been victimized by the mosquito, you deserve to know how it happened. Well, the source of irritation is not a mouth that opens and closes like your own. Rather, it is the female mosquito’s proboscis that causes the torment. Forming its center are six stylets, needlelike lancets set in six minute grooves. To be more specific, two stylets are mandibles, two are maxillae, one is the upper lip and the last a lancet with a channel for saliva. When not in use, these stylets are covered by the lower lip, which promptly moves out of the way when Mrs. Mosquito decides to ‘let you have it.’ She jabs you with her armed proboscis, and you may not even be aware of the wound unless she hits a sensitive spot, because the “lady” gives you a quick-acting anesthetic.
The puncture completed, Mrs. Mosquito’s saliva flows freely into the wound. Since this thins your blood and keeps it from coagulating, she has no trouble in sipping it through a groove in her upper lip, just as a person might sip soda through a straw. The drinking spree over, the “lady” removes her “needle” and flies away quite satisfied with perhaps three or four times her weight in your blood. Unwittingly, you have contributed to the increase of the mosquito population, for Mrs. Mosquito needed your blood to develop the eggs inside her body.
Since only female mosquitoes assault humans and animals, you may have a more friendly attitude toward the male. His fare is plant nectar. Actually, such juices are the chief food of the female mosquito too, but you may wonder about that after an encounter that leaves you with an itching welt.
Contending with the Foe
To ward off the insect menace of the night, people living in the tropics often sleep under mosquito netting. Also, various other steps are taken to avoid mosquito-transmitted diseases. One way in which yellow fever can be prevented is through the use of a vaccine. Malaria control ranges from insecticide use to swamp drainage and spraying chemicals or oil on breeding areas. A thin film of oil on the water prevents larvae from breathing because they are unable to get air at the surface.
Control of filariasis depends largely on the use of insect repellents and insecticides. Man has fought mosquitoes by draining marshlands or spraying insecticides over wide areas of field and forest. Individuals spray insecticides in their houses, hoping to put an end to mosquito forays.
How do repellents work? Well, the moist, warm, carbon-dioxide-laden stream of air around a person attracts mosquitoes. Sensory hairs on their antennae detect the stream and the insects eventually locate the source. But insect repellents generally foil Mrs. Mosquito because these apparently prevent the moisture sensors on her “feelers” from functioning normally. In a way, she gets the idea that she has missed her object and so flies elsewhere.
Experiments undertaken by Dr. W. A. Brown at the University of Western Ontario indicate that the kind of clothing you wear affects your “attractiveness” as far as mosquitoes are concerned. Allen Rankin writes: “In his experiments Dr. Brown found that one tenth as many mosquitoes landed on white clothing as on dark. In general, the lighter the color, the fewer mosquitoes attracted. Texture most avoided—luminescent satin.”—Marvels & Mysteries of Our Animal World.
Are They Any Good at All?
That is a good question, and likely many people would say, “No. Mosquitoes are no good!” But some researchers suggest that the male mosquito, whose fare is the juice of plants, plays a part in pollinating wild flowers of some types. Also, mosquitoes are said to be a significant food source for certain animals, birds, other insects and even fish.
Not all mosquitoes are dangerous villains. Disturbing though these insects can be, they do serve useful purposes. At least you need not fear every mosquito, even if you view their kind as the insect menace of the night.