December 2003

Mosquitoes - What good are they?

            What important function do mosquitoes provide in the natural order of things? To gain an understanding of what niche mosquitoes fill in nature we need to take a look at the order of insects they belong to, the Diptera or flies.

            Dipterans are characterized by a pair of membranous wings and a pair of slender, knobbed hind-wings used as balancing organs, called halteres. The order Diptera is a large one, with over 15,000 species in North America, alone. The larval stage of flies are moisture-loving, living in water ( like mosquito larva), decaying fruit or flesh or inside the living tissue of other animals or plants. A few live in relatively dry soil or move about exposed to the air, but these are the exception rather than the rule. Basically, the larval stage of flies consume decaying organic matter as a food source to support their growth and development. Mosquitoes in the larval and pupal stage provide a food source to fish or other aquatic organisms. Without mosquito larvae however, such predatory creatures would find something else to satisfy their hunger. So, as far as the food chain is concerned, their value is minimal and easily substituted.

            The food and habitat of most adult fly species are usually different from that of their larvae. Most adult flies feed on nectar and plant sap or on free liquids associated with rotting organic matter. Adult flies such as horse flies, deer flies, black flies and mosquitoes feed on blood for egg production and nectar for energy, only the females take blood. When in the process of obtaining nectar from flowers, mosquitoes will act as pollinators, thus contributing to an important process in nature, plant fertilization. However, if mosquitoes did not obtain plant nectar and pollinate plants in the process, there are a myriad of other insects such as bees, butterflies, moths, aphids, ants and other crawling and flying insects that would carryout the process of pollination. So in the grand scheme of things, mosquitoes as pollinators are easily replaced.

            So the question remains - what is the purpose of mosquitoes in the natural order of things? Because mosquitoes are flies maybe the question should be- what is the purpose of flies in nature? The purpose served by flies is that they transport microbes (bacteria, viruses, fungi, parasites), on their feet and mouthparts, throughout an ecosystem, quickly. When they feed, take flight and land on something (other organic matter), they transfer, by contact, their payload of microbes to these new habitats. As a transport system for microbes, flies stimulate the decay process, a very important part of a healthy ecosystem. Unfortunately, in their travels, they also spread microbes that cause food-borne diseases such as cholera, salmonellosis, dysentery and typhoid fever.

            Mosquitoes are different; they still function as a transport system for microbes but instead of causing food-borne illness like some other flies; mosquitoes cause mosquito-borne illness with the microbes they transport. Microbes that infect mosquitoes and cause mosquito-borne illness are picked up directly from an infected host. These viruses, protozoans or other microscopic organisms (microbes) that get into a mosquito and survive, uses (parasitizes) the mosquito to multiply their numbers and in some instances, go through specific life stages that can only occur while in the mosquito. So the blood sucking, ecto (external)-parasitic mosquito, not only acts as a host to these endo (internal)-parasitic disease organisms but also transports and injects them into another host animal when the mosquito takes a bloodmeal. Once in the host animal, these disease-causing organisms multiply and cause death or complete their life cycle and make the newly infected host animal a new source of the disease organism.

            So what benefit are mosquitoes to the natural ecosystem if they are not involved in the decay process like other flies, not a vital part of the food chain, easily replaced as pollinators of plants, and whose main function seems to be a transport mechanism for disease organisms? From man’s perspective, mosquitoes are a scourge that has caused more death and misery than anything in the span of human history. From an ecological perspective, mosquitoes, as transporters of disease and parasites, helps to maintain the balance needed for a natural ecosystem to function efficiently and remain “healthy”. Parasites and disease are essential to a healthy ecosystem. They are the gatekeepers, the policemen, so to speak, that enforce the laws of nature. Without disease and parasites, animals would exceed the carrying capacity of their environment. Once this occurs, the food chain would collapse and the animals would die from starvation. Mosquitoes and other flies, by transporting microbes that can cause death and disease, exert a survival pressure on organisms. This pressure stimulates organisms to adapt, evolve and maintain the proper population (balance) in the natural ecosystem. As such, mosquitoes and other flies are indispensable in nature. However, in the “ecosystem” modern man has created, the eradication of mosquitoes would probably be one of humankind’s greatest achievements.