The mosquito species Aedes aegypti arrived in the metropolitan area of Las Vegas, Nevada, eight years ago and, despite the arid conditions, has found a foothold. A new study finds the species to be present in more than half of census tracts in the area, causing concern about rising risk of vector-borne disease. (Photo by Gustavo Fernando Brahamian via iNaturalist, CC BY-NC 4.0)
By Ed Ricciuti
Ed Ricciuti
What happens in Vegas is supposed to stay there—but not when a mosquito capable of spreading a dangerous brew of diseases shows up and decides to put down roots there. The surprising discovery that Aedes aegypti, popularly known as the yellow fever mosquito, has found a home in the bone-dry Las Vegas metropolitan area has been spotlighted repeatedly by the news media since first detected there eight years ago.
“A Ticking Time Bomb” is how NBC News described the mosquito arrival in the gaming mecca. Another news account claimed the town’s hotel industry, already in a slump, was hiding the mosquito’s presence from visitors, a difficult task given the publicity it has received.
No question that the issue will not go away. Aedes aegyptii appears in Vegas to stay “despite the harsh, hot, dry summer weather conditions” of the region, according to new research published in September in the Journal of Medical Entomology. It outlines how the species is rapidly expanding its foothold in the Las Vegas area. Five years of trapping mosquitoes by scientists showed a 53 percent increase in the number of areas surveyed there showing Ae. aegypti presence.
“Our findings show that Aedes aegypti mosquitoes—which can transmit several arboviruses such as dengue, yellow fever, chikungunya, and Zika—are now established across much of the Las Vegas metro area,” says Saul Lozano, Ph.D., medical entomologist with the U.S. Centers for Disease Control and Prevention’s Division of Vector-Borne Diseases and lead author on the study. “This raises concern about the increased risk of possible local transmission if these viruses are introduced to the area.”
He adds an important caveat, though: The mosquito’s presence does not ensure disease transmission. Risk to people develops only if viruses are introduced and the vector is present, plus enough time for replication inside the mosquito, before it dies in a month or less.
Still, the specter of disease hangs over the area. While it might seem as if the arid environment of the desert in which Las Vegas lies is inhospitable to mosquitoes, that is not necessarily the case for Ae. aegyptii. The female needs only a small amount of water and just a few to lay its eggs. The eggs can survive for months without water and, once submerged, can hatch, pupate, and emerge as adults in a little more than a week. A discarded jar or birdbath can hold enough water for production of a new generation, and Ae. aegypti can establish itself if the lowest winter temperatures do not kill latent eggs.
While the ideal temperature for hatching eggs of the species is 77 degrees Fahrenheit, even a few are known to hatch at temperatures well below freezing, even 14 degrees F. A warming climate is the wild card because it could aid the mosquito’s expansion.
The fact that the mosquito is prospering, say the researchers, overturns predictions that it was unlikely to gain a foothold in the Las Vegas area, at least for now.
Originating in Africa, Ae. aegypti is now considered the most widely distributed mosquito, ranging across warm regions throughout the globe. It is highly adaptable, says Lozano. “It is possible that temperature and weather patterns in the Las Vegas area now allow for Ae. aegypti to survive,” he says. “Changes in local conditions can allow for pockets of suitable habitats to emerge in new places.”
Researchers have monitored the presence of the mosquito Aedes aegypti in the Las Vegas metropolitan area since its arrival in 2017 using census tracts in the area. In 2017, five of 117 (4%) surveyed census tracts were positive. By 2023, the number of positive census tracts increased to 147 of 276 (53%). (Image originally published in Lozano et al 2025, Journal of Medical Entomology)
The researchers apportioned their trapping by census tracts, small areas defined by the U.S. Census Bureau for taking census survey data. Tracts usually have between 2,500 and 8,000 people.
“In 2017, five of 117 (4%) surveyed census tracts were positive,” Lozano and colleagues report in their study. “By 2023, the number of positive census tracts increased to 147 of 276 (53%).”
Trapping was initiated based on public reports of nuisance mosquitoes. The authors cautioned that this fact might color the results of the survey but, nevertheless, stuck to their conclusions about the mosquito’s hold increasing.
Ae. aegypti likely spread into Nevada from California, where it was first discovered in 2013. It apparently moved north from Mexico on two separate occasions, several years before it was detected. The species has established strongholds in several parts of the Southwest, even at high altitudes in places and notable in and around Phoenix, Arizona.
At first, its abundance in the Las Vegas area remained consistently low, with no clear seasonal trend. In 2022 and 2023, however, there was “a marked increase in mosquito abundance, particularly from late August to October. The peak abundance in 2023 was substantially higher than in previous years,” the researchers say.
Rainfall during the research varied from year to year, with heavy rains from the remnants of Hurricane Hilary coinciding with a rise in mosquito complaints from the public in 2023. The increase may also have been due to media coverage and increased public awareness of mosquitoes, the researchers say.
Their study “highlights the need for effective vector control measures and public health strategies to mitigate the growing risk of vector-borne diseases in Las Vegas and other urban areas experiencing similar introductions of Ae. aegypti,” they write.
Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His most recent book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.
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