Every year, mosquitoes from across Texas are trapped, packaged, and bussed to a state lab in Central Austin. From there, a team of scientists meticulously sorts and tests the tiny insects for harmful viruses, searching for early warning signs that a new outbreak may be on the horizon. Last mosquito season alone—which peaked in the late summer months—they tested 200,000 of the bloodsuckers for diseases like dengue, chikungunya, West Nile virus, and Zika.

“Mosquito-borne diseases are so unpredictable,” says Bethany Bolling, team lead at the arbovirus entomology laboratory inside the Texas Department of State Health Services. “And as a state, we’re pretty vulnerable.”

The last time Texas experienced a serious mosquito-borne disease outbreak was back in 2016 when Zika—a virus that can cause severe birth defects and lifelong disabilities—exploded across the Americas with more than 700,000 cases, including nearly 325 in Texas. While the U.S. hasn’t reported a case of locally acquired Zika since 2017, public health experts warn the next flare-up is only a matter of time. “Another outbreak,” Bolling says, “is always just around the corner.”

Mosquito experts are understandably on edge. Between 2004 and 2016, according to the Centers for Disease Control and Prevention, Texas reported more than 6,600 cases of human disease stemming from mosquito bites, putting it in the top 20 percent of states for mosquito-borne illness. Nationwide, cases of reported diseases from vectors like ticks, fleas, and mosquitoes more than tripled over that same time period. In Austin and Travis County—like the rest of the country—West Nile virus has been the most common mosquito-borne virus, with more than 170 reported cases since 2007.

To control the insects’ local populations, Austin Public Health (APH) staff sets up about 30 mosquito traps a week in neighborhoods around the city and sends the specimens to the state lab for testing. This surveillance (which kicks off in May and runs through November) provides vital data that APH uses to map out changing mosquito patterns across the city’s ZIP codes all season long. For example, if data indicate a change in mosquito numbers, APH staff might begin searching for new breeding habitats. And if the bugs test positive for disease, the department is ready to scale up targeted outreach on how to avoid getting bitten. “We can’t control all the potential factors [that impact the risk of mosquito-borne illness], which is why surveillance is so important,” says Marcel Elizondo, program manager for Environmental Health Services at APH. “Without active surveillance, we wouldn’t know what’s coming into the city.”

Austin is home to a variety of disease-carrying mosquitoes, says Charles Crow, an environmental health officer at APH. If you’re getting bitten at dusk or dawn, it’s most likely a mosquito of the Culex species, which can transmit West Nile virus. There’s also the Aedes aegypti, commonly called the yellow fever mosquito, which is known to carry viruses like dengue (nausea, vomiting, rashes), chikungunya (fever, joint pain), and Zika. The Asian Aedes albopictus, another known carrier of Zika, is an especially risky type of vector because it’s active during the day.

On the commercial side, national pest companies like Orkin and Terminix rank Austin among the country’s top 50 mosquito-sensitive cities based on the number of customers served. The city’s warm, muggy climate is an especially strong indicator of what to expect; heavy, early spring rain typically ushers in a particularly bad mosquito season, says Mark Ambrose, division manager for pest control at Austin-based ABC Home & Commercial Services. Cleaning out your gutters and remaining vigilant about standing water goes a long way, he says. “Something as tiny as a bottle cap holds enough water for a mosquito to lay its eggs,” he says. “Anything that can hold water is a breeding site.”

Despite these city-wide efforts, scientists expect rising temperatures, fueled by climate change, will make controlling mosquito populations increasingly difficult in the coming years. At the same time, populations of Culex mosquitoes have already shown resistance to at least one insecticide, says Scott Weaver, principal investigator at the Western Gulf Center of Excellence for Vector-Borne Diseases at University of Texas Medical Branch in Galveston.

Back in the state arbovirus lab, Bolling and her colleagues are hatching mosquito eggs from around Texas and testing their resistance against insecticides used in the vectors’ home jurisdictions. While there’s no single solution to stopping the insects from jeopardizing our public health, this new data will offer invaluable insight into how to stay one step ahead of them. “There are so many variables that play into the transmission of mosquito-borne diseases,” she says. “The bottom line is to stay prepared.”