It’s not difficult to accidentally learn too much about bugs. Unfortunately, though, we have to, because they’re spreading out, inventing new ways to torture us and just generally making life less pleasant.
Take houseflies: They thrive in warmer temperatures, and it turns out they’re not just annoying; they can also be what bug nerds call mechanical vectors of disease. Put simply, it means they walk through garbage and then around your countertops, leaving salmonella and untold other pathogens along with their tiny fly footprints.
Or how about longhorned ticks? They first popped up on American shores in 2017 — and they can clone themselves. Female ticks just make thousands of self-Xeroxes; on the extremely rare occasions males are produced, it’s thought to be by mistake. Unsurprisingly, they’re a growing concern for the US, too.
In another especially science-fictiony case, ticks’ very saliva can spark a severe allergy to such delights as ice cream and hamburgers.
And that’s not even to mention the New World screwworm.
Because of climate, weather, acorn abundance (yes, really) and decisions about land use dating to colonial times, the bugs are indeed getting worse.
From a disease standpoint, it’s undeniable that bugs are posing an ever-larger problem. Reported cases of vector-borne diseases doubled between 2005 and 2019, according to US Centers for Disease Control and Prevention data, and we keep discovering new pathogens — 10 in the previous 17 years.
“Not that I’m trying to cause unnecessary concerns, but I see this as a tip of the iceberg,” said one Connecticut tick expert, Dr. Goudarz Molaei, who’s been tracking a rise in tick numbers and cases of disease across his state. “Right now, they are mostly limited to the coastal areas, but in a few years, as the warming pattern continues, these will move from coastal regions inland.”
And ticks are indeed the primary culprit behind vector-borne disease in the US, although worldwide, mosquitoes are bigger perpetrators, mainly because of the toll of malaria. (Mosquitoes are getting worse here too, but more on that later.)
Ticks in the US can transmit more than a dozen diseases, Lyme most of all. Experts, discouragingly, describe the trajectory of tickborne maladies as “explosive,” and not limited to Lyme.
“Lyme, babesiosis and anaplasmosis are all dramatically on the rise, with no sign of slowing down,” said disease ecologist Dr. Richard Ostfeld, who charts such depressing trends as a distinguished senior scientist for the Cary Institute of Ecosystem Studies in Millbrook, New York.
As many as 476,000 people a year in the US may be diagnosed with and treated for Lyme disease, an estimate based on insurance claims data, as cases may be underreported. It can be treated effectively with antibiotics, particularly when caught early, but can cause longer-term problems including arthritis, severe headaches and irregular heartbeat if not.
Babesiosis can cause flu-like symptoms and destruction of red blood cells, and it affects thousands of people in the US each year, though considerably fewer than Lyme, according to the CDC. Anaplasmosis can also cause severe illness, including respiratory failure, bleeding problems, organ failure and death, though it can also be treated with antibiotics, especially if caught early. It affected about 7,000 people in the US in 2023.
Another tickborne illness, Powassan virus, has been rising as well, although it is much rarer: As of 2025, it affected a reported 76 people nationally. It too can be severe, causing encephalitis, or inflammation of the brain.
This year, visits to emergency departments across the US for tick bites are at the highest they’ve been at this point in the season in the past seven years, according to data from the CDC, though they didn’t reach as high a peak as some previous seasons. They’re highest in the Northeast but elevated in all regions.
Part of the problem is that ticks are spreading out.
“There definitely are ticks in places where people grew up not having to worry about ticks,” said Dr. Erika Machtinger, an associate professor of entomology at Penn State.
Blacklegged ticks, which carry the bacteria that cause Lyme disease, as well as the parasites that cause babesiosis and the bacteria that cause anaplasmosis, doubled the number of counties in which they’re considered established between 1996 and 2015.
We can’t blame climate change alone for their spread, although we can blame it a little. The ticks are moving not just into previously colder climates, which are now becoming friendlier to them, but south into warmer ones.
“It’s complicated,” Machtinger said. Climate plays a role, but so do “factors related to landscape changes in the United States since the turn of the century.”
Deer — undergoing their own explosion in numbers after nearly being wiped out in certain regions of the US by deforestation and over-hunting — don’t carry Lyme-causing bacteria, but they do carry ticks around. White-footed mice, which do carry the culprit bacteria — charmingly named Borrelia burgdorferi — thrive in areas disturbed by people, according to Ostfeld. And people are increasingly good at disturbing things, through means like suburbanization.
Chipmunks, in another fact it’s impossible to forget once learned, can also be carriers.
And though the trajectory of tick-borne diseases in the US is indisputably pointing up, there’s variability in how bad things are from year to year, region to region.
The best predictor of how many ticks are likely to be around each year is how many white-footed mice were present the previous summer, Ostfeld told CNN. “And the best predictor of mouse numbers,” he said, “is how many acorns fell from oak trees the previous fall.”
Lots of acorns one year means lots of mice the next, which gives baby ticks a greater chance of biting a mouse and surviving long enough to bite us.
That progression led to a particularly bad year in some regions in 2025.
And findings from the field this year in places like Connecticut support the CDC data on higher-than-usual ED visits for tick bites, said Molaei, a medical entomologist at the Connecticut Agricultural Experiment Station’s Tick Testing Laboratory.
The numbers they’re seeing this year, both in submissions of ticks to be tested for pathogens and in their sweeps in nature, are “substantially higher” than last year and any going back to 2017, the previous high, Molaei said.
What’s more, he said, more of those ticks are testing positive for Lyme-causing bacteria: about 40% of blacklegged ticks submitted for testing this year, compared with 32% historically. Twelve percent to 14% carry babesiosis parasites and 7% to 8% the bacteria that cause anaplasmosis.
“In the past few years, we have seen higher prevalence of infection with these, particularly babesiosis,” Molaei added.
And up to 10% of ticks they test are infected with two or even three pathogens.
“You can imagine that causes substantial challenges for diagnosis and treatment,” he said.
Not to be outdone, other tick species are also spreading out and causing more misery. The aforementioned allergy to things like ice cream and hamburgers, for example, is called alpha-gal syndrome, and it’s spread in the US by the bite of another tick, called the lone star.
They’re concentrated in the Southeast, but lone star ticks have been making their way north and creeping in from the coasts. They particularly rely on white-tailed deer as hosts. Their saliva contains a sugar molecule found in mammalian products that, when introduced to us through their bite, can trigger an allergy to red meat and sometimes dairy.
The CDC estimates that as many as 450,000 people in the US may have alpha-gal syndrome. It’s getting particularly bad in areas like Martha’s Vineyard, the summertime island destination off the coast of Cape Cod, in Massachusetts, where an increasing number of residents have had to switch to vegan diets.
A particularly tick-friendly place due to its climate and overabundance of hosts like deer, Martha’s Vineyard is also coping with a rise in the self-cloning tick, the Asian longhorned. Island biologist Patrick Roden-Reynolds told CNN he found two of them on the island in 2023, the first year he identified them there. Last year, he collected 50.
“Right now, we don’t really know how much of a public health concern these ticks are going to be,” he said. But they’re making him nervous.
In their native range, longhorned ticks do bite humans and can transmit certain types of encephalitis, Roden-Reynolds said, but so far their bigger concern in the US has been as an agricultural pest. The US Department of Agriculture notes that they’ve now been found as far south as Georgia and as far west as Missouri.
Though ticks take a bigger toll when it comes to disease in the US, mosquitoes are plenty bad — and expanding their ranges, as well.
The US eliminated malaria — the deadliest mosquito-borne threat globally, and the one responsible for making the mosquito the world’s deadliest animal — in 1951, although locally acquired cases have popped up sporadically.
The bigger mosquito-borne problems in the US are West Nile virus and dengue fever, which are carried by two different genuses of mosquitoes.
West Nile, spread by mosquitoes in the Culex genus, affects about 2,000 people every year in the US and causes about 130 deaths, and this season is off to an early and ominous start, the CDC warned. Dengue, spread by Aedes aegypti and Aedes albopictus mosquitoes, caused about 4,000 locally acquired cases in the US in 2025 and has been particularly problematic in Puerto Rico.
Aedes mosquitoes can also transmit the viruses that cause chikungunya, Zika and yellow fever, and they’ve been expanding their range. The first Aedes aegypti in California were detected in 2013, and they’ve been spreading north since. The first in the state of Idaho, previously not thought to be within the mosquito’s territory, was discovered in August.
Overall, Aedes aegypti are estimated to be spreading northward in the US at a rate of about 150 miles per year, according to research from the Yale School of the Environment, and climate change could further accelerate their move over the longer-term.
More acutely, mosquito populations are affected by the weather, said Dr.
Jim Fredericks, an entomologist and senior vice president of public affairs at the National Pest Management Association.
“Pest populations and pest biology is really closely tied to things like temperature and precipitation,” he said. And his group predicted an especially buggy year across the US this year, with a mild, damp spring boosting mosquito populations early in states from Texas to Mississippi and tropical storms triggering mosquito surges from standing water in the Southeast.
Flies, those mechanical vectors of disease, may also be worse this year because of weather patterns across much of the US. And the flesh-eating New World screwworm — which in its adult phase is a fly — may benefit from both climate and weather patterns as it re-establishes itself in the US after 60 years. They can lay eggs in wounds as small as tick bites, a horrifying cycle of bug benefiting bug.
Oh, and finally, the Southwest is expected to have an especially pesky year for scorpions — yes, they’re arthropods, too! — as they and fellow arachnids like spiders are driven indoors by monsoon rains.
The good news is prevention of the plagues brought by bugs is possible.
When it comes to ticks and mosquitoes, wearing Environmental Protection Agency-registered repellent is recommended. Treating clothing and shoes with permethrin, a repellent that’s safe for people but bad news for bugs, is an especially helpful extra layer of protection.
Maintaining the environment around your home to make it less enticing to bugs can also make a big difference: eliminating standing water, a breeding ground for mosquitoes, and moving leaf litter, where ticks like to hang out, away from heavily trafficked areas. That’s also a good tip for thwarting scorpions: moving woodpiles, trash and debris from around the home, repairing holes in screens and cracks or holes on a home’s exterior.
And as the bugs make their moves, science isn’t standing still. Drug giant Pfizer has said it’s applying for approval of a Lyme disease vaccine, which would be the first on the market in two decades if cleared by the US Food and Drug Administration. Work is also underway to develop other methods of protecting people from ticks, including a pill in clinical trials that aims to kill them after they bite, preventing them from spreading pathogens.
For alpha-gal syndrome, the tick-caused meat allergy, doctors are increasingly turning to the allergy and asthma drug Xolair to tamp down the risk of bad allergic reactions. There is also a suggestion that a certain kind of acupuncture may help.
And then there are the more futuristic approaches: genetically modifying mice, for example, so that they can’t carry the Lyme-causing bacteria, a potential endeavor on an island in Nantucket. Or the older-school ones: An island in Maine eliminated all of its deer. It’s far enough from the mainland that deer can’t swim there (a thing they apparently can do in some places) and repopulate. The island’s Lyme disease incidence flattened.
But all of these methods come second to taking steps to protect ourselves directly, experts emphasize.
“The most important thing that people can do is personal protection,” said Molaei. “Nothing can match this one.”
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