Two dangerously invasive Mosquitoes — male and female — have been trapped in Santa Clara County, the latest evidence that the disease-carrying species could colonize the San Francisco Bay Area.

The detections follow a similar sighting in Watsonville last week, and another in Martinez last August. They have not been spotted in Alameda or San Mateo counties.

“We were expecting it. It was just a matter of time,” said Nayer Zahiri, manager of the Santa Clara County Vector Control District.  “It was a little bit of a surprise, of course, but we were ready.”

None of the mosquitoes, named Aedes aegypti, were carrying Zika, dengue, yellow fever, chikungunya or any of the other deadly viruses that they are known to spread. While the county has had occasional cases of those diseases among returning travelers, they were not transmitted by insect.

But the discoveries are prompting calls by pest control experts for residents to drain and clean any water source where the insect can multiply. The eggs — sticky and small, like black dirt — are laid on the inner walls, above the water line, of buckets, plant saucers, birdbaths, clogged gutters, pet bowls and even bottle caps.

Winter won’t eliminate them. The eggs can survive for more than a year, even if they dry up, and will hatch as soon as they’re wet again.

Native to West Africa, the insect terrified the world in 2015, when it quickly spread the Zika virus across Brazil and more than 50 other countries and territories. Zika can cause debilitating birth defects, including microcephaly, with brain damage so profound the consequences are only beginning to be understood.

The mosquito was first found in Southern California about two decades ago. Since then, it has spread northward into 20 California counties, from San Diego to Shasta, in a pattern that hews to the Central Valley’s Interstate 5 freeway.  Based on a genetic analysis, the California bugs were likely introduced from the southeastern United States.

Its expansion in California is causing such concern that vector control officials are planning to introduce 2 million genetically modified mosquitoes in Tulare County, with potential expansion into Fresno, San Bernardino and Stanislaus counties. When these lab-built insects mate with wild insects, their offspring die, causing an eventual collapse of the population.

Until now, the Bay Area has been largely spared. While the mosquito has been spotted here before — a few were found in San Mateo and Alameda counties between 2013 and 2015 — they’ve never secured a firm foothold.

In Southern California, the mosquito is here to stay. “They’re established, because they’re really hard to get rid of,” said Edgar Nolasco, director of Santa Clara County’s Consumer and Environmental Protection Agency.

The mosquitoes found this week were located in a commercial business district in North San José near the Milpitas border, near the intersection of Dixon Landing Road and McCarthy Boulevard. They don’t thrive in the region’s natural areas; rather, they prefer city life, near people.

An intensely black mosquito, it is distinguishable by its pointed abdomen and two white stripes in the shape of a lyre on its back and white bands on its legs.

California has about 35 native mosquitoes. Most bite in the evenings, when people tend to be indoors. The most worrisome, a nondescript brownish insect named Culex pipiens, transmits West Nile virus. This is usually the one you hear buzzing in your ear at night. But the vast majority of native mosquitoes do not transmit any disease.

These new invaders hunt for blood during the day, when people are outside. They’re aggressive, biting repeated times. But they don’t travel far. Known for lurking in foliage, they’re homebodies, rarely flying more than a block from where they were born.

The female mosquito was caught first, in one of the 40 to 50 small traps that are set all over Santa Clara County in a grid system of surveillance.

To lure the insects, the traps use dry ice as an attractant. That’s because dry ice emits carbon dioxide, which is what humans exhale — so the mosquitoes are fooled into thinking that the trap is a source of blood.

Out all night, the traps are collected every morning. Caught insects are frozen in the traps and then tediously hand-sorted and identified, using tweezers, under a microscope.

“As soon as we saw what was in their traps, we put it aside, because it was not a common mosquito that we see every day,” said Zahiri.

The male was caught later, in an expanded trapping effort around the neighborhood. Photos were taken and shipped to insect experts in Sacramento for confirmation.

Since then, “luckily, we have not found any other of the mosquitoes,” said Nolasco. “But that doesn’t mean we’ll put our guard down. Its eggs can live up to a year.”

How to prevent mosquitoes from breeding near you:

• Dump out even the smallest amount of standing water. Cleaning and scrubbing bird baths, pet dishes and other containers is a good way to remove any lingering Aedes aegypti eggs.

• Properly screen rain barrels, cisterns and irrigation drains to prevent mosquito access.

• Fix leaky water faucets and broken sprinkler heads and avoid overwatering lawns and plants.

• Make sure the water level of swimming pools is adequate for proper circulation and filtration.

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To protect yourself from mosquito bites:

•Apply insect repellents containing EPA-registered ingredients such as DEET, picaridin, IR3535 or oil of lemon eucalyptus, always following label instructions.

•Wear long-sleeve shirts, pants, socks and shoes when mosquitoes are most active.

• Make sure your window and door screens are in good condition.

If you get bitten by a mosquito during the day, report it immediately to the Vector Control District at (408) 918-4770 or [email protected].