Bzzzz...Slap!

By Text by Jeffrey Kluger

The rains that recently drenched the East have swelled ponds and left standing water in everything from flowerpots to abandoned tires--perfect skeeter-breeding pools. That would be bad news any year, but with mosquito-borne West Nile virus beginning its fifth summer in the U.S., health officials are increasingly worried. Controlling the maddeningly efficient insects may be the only effective way to control the sometimes deadly disease. Here's what scientists know about the operation of these ingenious stinging machines.

A MOSQUITO LOCKS ONTO A POTENTIAL VICTIM...

Male mosquitoes live quite peaceably on plant nectars and juices high in sugar, but females need protein from blood to nourish their eggs before depositing them. They get it from humans and animals and rely on an array of senses to ensure that they rarely fly wide of a possible meal

HOW THE INSECT LOCATES US

C02 Mosquitoes detect exhaled carbon dioxide and follow this vapor trail until they reach whatever is breathing

ODORS Nearing the target, the bugs are able to detect lactic acid secreted by the skin, proof that they're still on course

TEMPERATURE Body heat is also a mosquito magnet, which is why heat-absorbing dark clothes put you at greater risk

...AND UNLEASHES HER FEEDING TOOLS

1 SKIN IS PIERCED A shroud called a labium opens as the hungry mosquito readies herself to bite, revealing fine cutting instruments called stylets

2 SALIVA IS INJECTED The mosquito injects an anticoagulant mixed with saliva through the hypopharynx. This keeps blood flowing easily. It also causes an itchy bump to rise

3 BLOOD IS DRAWN Drinking its fill may take a mosquito a good five minutes. The fine, strawlike labrum (barely wider than a blood cell) draws slowly but also prevents the host from feeling the bite

Sources: USGS, Rutgers, American Mosquito Control Association, The Way Nature Works

LIFE CYCLE Females hunt for standing water in which to lay their eggs. Four stages follow, which vary in length, depending on species

EGG 24 to 48 hours A clutch of 100 to 300 eggs is laid to form a tiny raft

LARVA 4 to 14 days So-called wigglers hang just beneath the surface and breathe through a tube

PUPA 1 to 4 days Known as tumblers, these premosquitoes are almost ready to become full-blown pests

ADULT Days to months As soon as they emerge from the water and harden on its surface, they fly off to feed and mate

TOTAL LIFE-SPAN 2 weeks to a few months

WEST NILE IN THE U.S. The West Nile virus, which infects the central nervous system, was first identified in 1937 in Uganda but did not appear in the U.S. until 1999. That year it sent 62 people to the hospital, killing seven. By last year those numbers had exploded to 4,156 cases and 284 deaths in 40 states. This year it is expected to strike every state but Alaska and Hawaii

TRANSMISSION Birds are prime reservoirs of West Nile virus and prime targets of mosquitoes. When a mosquito bites an infected bird like a crow, the virus collects in the insect's saliva and can infect the next target it strikes. The disease may take 3 to 14 days to incubate

THE RISK TO YOU Even where the virus is at large, only about 1% of mosquitoes carry it. If one of them bites you, the odds are still in your favor

Of 150 people infected, on average:

--120 show no symptoms

--29 develop mild flulike symptoms from which they will completely recover

--1 develops serious symptoms, including: headache, high fever, body aches, convulsions, coma and stupor. In extreme cases, potentially lethal encephalitis (inflammation of the brain) or meningitis (inflammation of the membrane surrounding the brain and spinal cord) may result

PROTECTING YOURSELF

NATURAL CONTROLS

--Minimize outdoor time from dusk through dawn --Wear long sleeves and long pants in loose-fitting, light-colored fabrics --Empty standing water in birdbaths, rain gutters and elsewhere --If you're camping, always use a mosquito-safe tent

CHEMICALS

Sprays that contain DEET can confound mosquitoes' lactic-acid receptors, sparing you a bite

Permethrin is a neurotoxin that is applied to clothing to kill bugs on contact

CULEX PIPIENS Main carrier of West Nile virus to humans

HEAD --Salivary glands --Compound eye --Palpus --Proboscis bundle (shown unsheathed) 1 Labium 2 Hypopharynx 3 Labrum Stylets (4) --ANTENNAE contain receptors sensitive to C02 and lactic acid. Thermosensors help the insect locate rich subcutaneous capillaries

THORAX --Foreleg --Middle leg --Hind leg

ABDOMEN --A mosquito will feed until its abdomen is fully distended --WINGS The West Nile skeeter normally travels a short distance from its breeding ground