It's hard to justify the existence of these annoying critters
Mosquitoes seem to serve no purpose other to annoy us. But from the mosquitoes' point of view, their purpose is to make more mosquitoes. From the point of view of birds, fishes, frogs and other animals that eat them, their purpose is to provide a source of food.
But does the world actually need mosquitoes? It's hard to find a reason.
An article by Janet Fang in the July 2010 magazine Nature asked scientists what the world would be like without mosquitoes.
Most of them thought that we wouldn't miss the annoying little creatures. Disease among humans would decrease, if the mosquitoes that spread malaria, dengue fever, encephalitis and other illnesses disappeared.
In the Arctic tundra, mosquitoes form dense clouds when they hatch. Birds which nest in that region might miss them as a source of food, if they disappeared. But other scientists say that mosquitoes don't make up a large enough part of the birds' diets, and they could survive on midges or other insects just as well. Caribou, which must deal with the onslaught of the mosquitoes, might change their paths, feeding in new places, and alter the ecosystem in localized areas of the Arctic.
Elsewhere, fish, frogs, lizards, spiders and other animals that eat mosquito larvae or adult mosquitoes would lose a food source. Mosquitoes make up a small part of the diet of some, but others, like the mosquitofish or gambusia, which specializes in eating the larvae, might become extinct. But most animals already eat enough of something else, or could change their diet, so they wouldn't go hungry without mosquitoes.
Mosquito larvae consume a lot of organic matter in wetlands, helping recycle nutrients back into the ecosystem, but other larvae and water-dwelling creatures also do the same and could take over that job.
Adult mosquitoes feed on nectar as well as blood--in fact, nectar is all the adult males eat--so some plants might suffer due to lack of pollinators if mosquitoes stopped visiting, especially northern orchids. Though this might alter things somewhat, the plants aren't necessarily crucial to the ecosystem.
The biggest effect, is that fewer people would die of mosquito-spread diseases, so there would be more humans on the earth, especially in countries that are already having trouble supporting their populations. But humans would be healthier, more productive, and not have to spend so much time and effort caring for those who were sick. "The romantic notion of every creature having a vital place in nature may not be enough to plead the mosquito's case," Janet Fang concludes, in the Nature article. "It is the limitations of mosquito-killing methods, not the limitations of intent, that make a world without mosquitoes unlikely."
Of course, when imagining a world without mosquitoes, one must imagine that they were killed in a way that was harmless to other creatures, and that's part of the reason we can't just eliminate them, as much as we'd like to. Insecticides kill not only mosquitoes, but other animals too. Even specially targeted natural larvicides, like those using Bti, kill a few closely related species such as black flies and gnats.
So even though mosquitoes don't seem to have a purpose, other than to cause us annoyance and misery, we can't just get rid of them right now, without doing more harm to other species that are more useful.
Images courtesy of acscom at Stock.xchng and Africa at freedigitalphotos.net.