The most dangerous bug in the world

StoryImage( ‘/Images/Story//Auto-img-11188569176883.jpg’, ‘Diagram by Dr. Robert A. Hedeen’, ‘Diagrammatic representation of a female mosquito’s mouthparts used to pierce the skin and suck blood. (From Naturalist on the Nanticoke.)’);

Sometime about 300 million years ago, a gnat-like insect succumbed to a strange new instinct that told her to try to force her mouthparts into the skin of a small lizard. Prior to this time, her countless relatives had been fairly successful in satisfying their nutritional requirements by sucking the carbohydrate-rich juices of plants. When this ancestor of the mosquito was finally able to penetrate the soft underbelly of the reptile and wriggle her beak into a tiny capillary, an abundance of an energy-rich viscous material flowed into her gut, and a new physiological way of life was instigated. This new instinct in behavior probably resulted from a mutation in her genetic makeup and was passed on to her offspring. Within a relatively short period of time, the blood-sucking family of mosquitoes was born.

Prior to 1898, mosquitoes were merely considered to be obnoxious pests, though a few scientists suspected them of transmitting serious diseases of man. In that year, Sir Ronald Ross, a physician in the British Army serving in India, discovered that the causative organisms of malaria required a period of development in the mosquito and were then transferred to another host when the mosquito bit. The importance of this discovery is evident today when the World Health Organization reports that malaria is still the No. 1 killer of mankind on the face of the earth. Malaria is only transmitted naturally by mosquitoes.

Some years before Ross’s discovery, Dr. Carlos Finlay in Cuba suggested that the infectious agent of the dreaded yellow fever, or yellow jack, was also transmitted to man by mosquitoes. A few years later, the American Army physician, Maj. Walter Reed, in a series of experiments using human volunteers, proved that Finlay’s hypothesis was correct.

These discoveries opened the door for extensive research concerning the role of the mosquito in the transmission of other diseases of man and lower animals. Within a few years, these two-winged members of the insect order Diptera were also incriminated as the vectors of the following human diseases, in addition to malaria and yellow fever: filariasis (a parasitic worm); dengue or breakbone fever; and a number of serious viral diseases of the central nervous system including, eastern equine encephalitis, Western equine encephalitis, St. Louis encephalitis, Japanese B encephalitis, LaCrosse or California encephalitis, and West Nile encephalitis, which has recently plagued the United States, especially Illinois.

About 3,000 different species of mosquitoes have been discovered worldwide, with about 170 different ones in North America. It is fortunate for us that only a very few of this multitude of different species have been incriminated as vectors of human disease, and only female mosquitoes suck blood. There are many serious diseases of lower animals that are transmitted by certain mosquitoes; the most important to us in northern Illinois being heartworm disease of dogs.

Vast amounts of money are spent each year to control mosquito-borne diseases. It is estimated that at least $200 million a year is spent by individuals for skin repellents and another $5 million on backyard mosquito traps and other protective devices. To actually control mosquito populations, tax-supported mosquito abatement districts are present in a majority of the states, including political subdivisions in Illinois. Budgets for these districts may run up to $1 million dollars a year. In areas with no organized abatement district, local health departments allocate funds for mosquito control when needed.

I have been asked many times if mosquitoes are of any benefit to mankind, and until some years ago, I had only been able to give vague, unsatisfactory answers. I then met an old waterman on the eastern shore of Maryland and was given a different slant on the question. We were talking about crabs and oysters, and the mosquitoes were attacking us with a fury. I told the man I was leaving as I could not tolerate the mosquitoes any longer. He replied, “ I didn’t know that you were so damn ignorant that you did not know we is always making blood in our bodies, and iffen the skeeters didn’t suck some of it out, we would all blow up and bust!”

Aside from the blow up and bust theory, most scientists will agree that as far as man is concerned, the mosquito is the most dangerous bug on earth.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

From the June 15-21, 2005, issue

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