LAS VEGAS \u2014 If at one time it was thought mosquitoes couldn\u2019t survive in desert climates, this city is a case study in how wrong that is.<\/p>\n\n\n\n
Mosquitoes typically prefer more tropical, humid conditions, but these biting machines have exploded in number throughout the Las Vegas Valley<\/a> in recent years because of a host of changes.<\/p>\n\n\n\n A mix of urban development, climate change, <\/strong>insecticide resistance and genetic adaptations are creating a more hospitable environment for the insects in southern Nevada.<\/p>\n\n\n\n Las Vegas is hardly alone in its battle against the pesky insects. Warmer temperatures and shifting weather patterns are expanding the geographic range in which mosquitoes live and breed. In many ways, what\u2019s happening here is playing out across the desert Southwest and beyond.<\/p>\n\n\n\n The mosquitoes have brought with them not only the nuisance of bug bites, but also the major threat of mosquito-borne diseases such as dengue fever<\/a> and West Nile virus<\/a> to Las Vegas and the rest of Clark County.<\/p>\n\n\n\n It’s also caught people off guard.<\/p>\n\n\n\n \u201cPeople aren\u2019t wrong that mosquitoes shouldn\u2019t really thrive in desert conditions, but it\u2019s clear that the particular set of species that we do have in Clark County has adapted to the local ecology,\u201d said Louisa Messenger, an assistant professor in the department of environmental and global health at the University of Nevada, Las Vegas.<\/p>\n\n\n\n The species that have taken hold in Clark County include Culex mosquitoes, which can carry West Nile virus, and Aedes aegypti mosquitoes, the primary spreaders of dengue. What\u2019s more, Messenger and her colleagues at UNLV have found that mosquitoes in Las Vegas are becoming resistant to insecticides<\/a>, a major public health risk in a city built on tourism.<\/p>\n\n\n\n \u201cIt is a little bit of a ticking time bomb,\u201d Messenger said.<\/p>\n\n\n\n She has for some time been concerned about how vulnerable Las Vegas is to mosquito-borne diseases. In particular, dengue has been surging in North America and South America, with more than 13 million cases recorded across the continents in 2024, according to the Centers for Disease Control and Prevention<\/a>.<\/p>\n\n\n\n \u201cIn Vegas, we have more than 48 million visitors coming through our doors every year from all over the planet,\u201d Messenger said. \u201cIt just takes a couple of mosquito bites to start local transmission.\u201d<\/p>\n\n\n\n Last year, there were 26 reported cases of West Nile virus in humans in Las Vegas, according to the Southern Nevada Health District<\/a>, trailing the city\u2019s largest outbreak of 43 cases in 2019. Yet, in 2024, scientists still found a record number of mosquitoes that tested positive for the virus<\/a> in and around the city, which suggests the risk of exposure was very concerning.<\/p>\n\n\n\n This year, the public health department hasn\u2019t identified any human cases so far, even as mosquitoes have tested positive for the virus in certain ZIP codes. Messenger said it\u2019s not well understood what specific factors fuel outbreaks in some years and not in others.<\/p>\n\n\n\n \u201cWe see these overlapping factors but they are quite difficult to tease it apart,\u201d she said. \u201cAll we can say for certain is that we have these bumper years and these zero years, and they are hard to predict.\u201d<\/p>\n\n\n\n The Southern Nevada Health District has been conducting mosquito surveillance in the region<\/a> since 2004. Its meticulous records show which mosquito species are present across the Las Vegas Valley year after year and where these flying insects have tested positive for diseases.<\/p>\n\n\n\n One of the most astonishing trends in the data was the explosive growth of Aedes aegypti mosquitoes, which were first identified in Las Vegas in 2017, said Vivek Raman, environmental health supervisor for the Southern Nevada Health District.<\/p>\n\n\n\n \u201cIn 2017, this mosquito was found in just a few ZIP codes,\u201d said Raman, who oversees the health district\u2019s mosquito surveillance program. \u201cA few years later, it was six ZIP codes. Then 12 ZIP codes, then maybe 20, and now it\u2019s in 48 different ZIP codes across the valley.\u201d<\/p>\n\n\n\n In addition to being able to spread dengue, these insects are a major nuisance.<\/p>\n\n\n\n \u201cAedes aegypti are very aggressive daytime-biting mosquitoes,\u201d Raman said. \u201cThey are just relentless biters.\u201d<\/p>\n\n\n\n Unlike Culex mosquitoes, which prefer breeding near larger sources of water such as untended swimming pools, culverts or detention basins, Aedes aegypti tend to breed in much shallower standing water.<\/p>\n\n\n\n \u201cOne of the reasons they are spreading so quickly is the mosquito can lay its eggs in small containers, like if rain fills a child\u2019s toy or tires or a wheelbarrow,\u201d Raman said. \u201cAll it takes is a couple inches of water.\u201d<\/p>\n\n\n\n Urban development in Las Vegas has also inadvertently spurred the spread of mosquitoes in the city. Golf courses, human-made lakes and other forms of artificial irrigation have all made this outpost in the Nevada desert a welcome home for mosquitoes, according to Messenger.<\/p>\n\n\n\n