They creep up on their victims without their knowing it, then leave them to suffer. They hunt their prey in broad daylight, when children are playing. They've resisted most efforts at eradication.
And they're born in the most seemingly innocuous places: gutters, birdbaths and tarps left out after a rain.
The most tenacious mosquitoes to hit the Washington region in a decade, Asian Tigers are swarming through Prince William in record numbers, mosquito control officials say. And they're making people crazy.
"They're driving us nuts," said Kathy Wade of Woodbridge, who has reason to worry. With up to seven children under age 9 in her charge for day care every weekday, Wade relies on her back yard to get through the day.
"I ask my kids if they want to go outside, and they say, 'No way,' " Wade said. "These things are very vicious. They'll attack you while you've got a can of spray in your hand."
The bugs have kept not only children indoors, but also kept adults, wreaking havoc with social lives.
"They've pushed the community inside," said Steve Kersse, president of the Featherstone Civic Association, in Woodbridge. The families in his neighborhood, Featherstone Shores, used to enjoy late-summer get togethers on their private beach.
"The mosquitoes have driven people away from that community place where we congregate," he said. "You can't sit on a picnic table or you'll get eaten up."
The Asian Tiger, aedes albopictus, has been spotted across Northern Virginia and Maryland for several years, and was first noticed in Prince William in 1997. But in the past few weeks, as the summer drought has turned into a very rainy September, the mosquitoes have flourished.
"It's been nightmarish," said Kim Largen, the county's gypsy moth and mosquito control branch chief. Complaints to her office have tripled in the last few weeks, she said.
In samples taken by county officials in 1997, the mosquito showed up in just three test sites across Prince William. Last month, they were found in 40.
The problem is worst in the county's eastern end, where houses are closest together. More sparsely populated Loudoun County has not reported an outbreak, health officials there say. But in densely developed Fairfax, environmental health specialist Pat Petro said her office has received 10 calls a week about mosquitoes during the last month.
"We just haven't verified if they're tiger mosquitoes or not," Petro said.
Black with bright white markings on their legs, thorax and abdomens, Asian Tigers are potential transmitters of Dengue fever and encephalitis, although no recent cases have been reported in the Washington area. The bug arrived in Texas in 1985 in a shipment of used tires from Japan.
The mosquitoes share few traits with their brethren. They're stealth bugs, descending on human skin without the familiar high-pitched whine and landing so delicately you can't feel them.
Instead of marshes, ponds or other wetlands, they need only a few teaspoonfuls of water to breed, with choice hatching places being tires, wading pools, even flowerpots. Unlike other mosquitoes, they love sunshine, hunting for food during the day rather than at dawn and dusk.
All of which makes them hard to get rid of. The county--the only jurisdiction in Northern Virginia with a mosquito control program--has sprayed the pesticide Anvil on 15,000 acres across Prince William since May.
But here's the rub. It's a lot easier to spray an entire marsh and get results than it is to spray a flower pot or a clogged rain gutter. And spraying at midday is less effective than at dawn or dusk, because heat causes the insecticide to rise and disperse.
"We spray, but people call us back in a day or two and say it didn't work at all," Largen said. "But we can't go door to door and drop a granule into into every nook and cranny that might be holding water.
The best solution is prevention, Largen said. This is to say, get rid of water around the house, no matter how obscure its collection spot. Trash cans and lids, pet dishes, ornamental ponds--all are susceptible.
And take comfort. The bugs won't be around forever. They don't survive after the first frost, which should arrive in October.