In India last year, I sat in a restaurant garden sipping tea and watching the sun sink behind the trees. An occasional whine near my head reminded me of the mosquitoes. I waved off the bolder ones and tried to remember which type they might be. Anopheles or Aedes? One carries malaria, the other carries dengue. I was taking mefloquine against malaria, but there is nothing to protect against dengue. Was it late enough in the afternoon to qualify as "dusk"? Some mosquitoes feed at night, others at dusk and dawn. Which did what? This is the problem with mosquitoes: There is so much to know about such a little pest. And the consequences of not knowing can be fatal.

Fortunately, answers to such questions are available in Mosquito: A Natural History of Our Most Persistent and Deadly Foe, a fascinating new book coauthored by Andrew Spielman, a professor of tropical public health at the Harvard School of Public Health. A few years ago, a book about mosquitoes might not have attracted much attention. Times have changed. As summer approaches, the eastern United States is girding for another outbreak of mosquito-borne West Nile virus. Dengue is being smuggled into Texas by border-crossing mosquitoes. Rhode Island is on the lookout for eastern equine encephalitis (EEE). Globally, a major international campaign to "roll back" malaria is under way. Clearly, Spielman's book is timely. Mosquito is part biology text, part history lesson, and part primer on the politics of public health and pesticides.

It is the female mosquito that needs blood, and so it is the female that does the biting. A few "drag queen" males called gynandromorphs also bite, though they have no use for blood. Consequently, most of our irritation comes from the female as she stabs through our skin 20 or more times trying to nick a blood vessel. That persistent probing provides ample opportunities to pass along malaria-causing parasites or deadly viruses.

Most of us seldom take the time to look closely at mosquitoes. We are too busy swatting nature's delicate nanotechnology into so much crumpled fuselage. After reading the authors' descriptions of the Alien-like metamorphosis of the mosquito, however, we may be inclined (at least once) to look first and swat later. The typical mosquito begins life as a floating egg, emerges to become a snorkeling larva, then a worm-like pupa, and finally a winged adult looking to feed and start the cycle anew. It bites and our blood becomes the nutrient for the next generation of eggs.

The biology of mosquitoes would not be terribly important to humanity but for the fact that in taking blood they often leave behind a hitchhiking pathogen. Depending on the mosquito and the location, it might be malaria; dengue; yellow fever; filariasis; West Nile, LaCrosse, Ross River, or Rift Valley virus; eastern, western, or Venezuelan equine encephalitis; St. Louis encephalitis; or some lesser-known virus. It is the mosquito as the vector of disease that elevates it above mere pest status. It has been an agent of epidemics, a shaper of history, and a fly in the ointment of international trade and commerce.

Spielman and D'Antonio write that Aedes aegypti, which transmits yellow fever, had as much impact on the history and character of the American South as slavery, cotton, and the Civil War. The mosquito and its viral cargo regularly decimated cities from New Orleans to Memphis.

The link between mosquitoes and diseases wasn't intuitively obvious to governments or physicians. It was not until the late 19th century that Patrick Manson in China and Ronald Ross in India discovered that mosquitoes transmitted filariasis (elephantiasis) and malaria. Suddenly, the British Empire could be made safer by attacking mosquitoes. In 1898, the United States was in danger of losing its own recently acquired empire to yellow fever. In U.S.-occupied Cuba, a physician named Carlos Finlay used the work of Manson and Ross to pinpoint a mosquito (Aedes aegypti, again) as the likely agent of yellow fever. But he had trouble convincing the slow-moving Walter Reed, head of the U.S. Army's Yellow Fever Commission, and more than once he must have felt like shouting, "It's the mosquito, stupid!"

With malaria and yellow fever identified as mosquito-borne diseases, efforts to suppress mosquito populations gained momentum. The first campaign in the United States centered on New Jersey's Meadowlands in 1900. Local development and recreation soared as mosquito populations and malaria cases plummeted.

Mosquito control really took off during World War II with the rediscovery of a 50-year-old chemical called DDT. It was stunningly successful in eradicating mosquitoes. "This is the DDT era of malarialogy," declared one enthusiast. "For the first time it is economically feasible for nations . . . to banish malaria completely from their borders." Spielman recalls that DDT's impact was so great the Harvard faculty stopped teaching and doing research on malaria. DDT was the solution, so what was the point of more research?

Then came the heartbreak of resistance: Quinine-resistant malaria parasites and DDT-resistant mosquitoes. Rachel Carson's 1962 book Silent Spring vilifying chemical pollutants was the stake through the hearts of DDT evangelists. Spielman must have been wounded too. He writes, "The total ban on DDT's use . . . deprived American public health officials of a weapon that could have been safely used. It is the ideal pesticide of first use. A worldwide ban on DDT would be a mistake." A new international treaty banning dangerous chemicals has left DDT off the list because of its effectiveness against malaria.

The book's take-home message is that mosquitoes are not going away. We have to live with them. It will not be easy. According to the authors, we are often as much to blame as the hungry mosquito. Our throwaway societies have created millions of water-filled containers for mosquito eggs. An international trade in recapped tires introduced the aggressive, virus-carrying Asian tiger mosquito, Aedes albopictus, into the United States. Replacing draft animals with tractors and trucks has forced local mosquitoes to find new blood supplies - people. International jets probably carried West Nile to the United States, where, according to the authors, the virus is expected to "creep westward."

Efforts are under way to create genetically modified mosquitoes incapable of causing disease. The authors have little faith in these high-tech approaches, but are optimistic about the World Health Organization's new campaign to cut malaria deaths in half by 2010.

The authors close with some advice on avoiding mosquitoes (use DEET-based repellents) and describe which mosquito bites when and where. But fundamental mysteries remain. No one knows what it is about blood that mosquitoes crave, and no one knows how they extract it through such a narrow proboscis. Research is not likely to stop again anytime soon.