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The most distinctive feature of lone star ticks may be the starlike white splotch on the backs of adult females that gives them their name. But it’s the baby (larval) lone star ticks that may make a bigger impression. That’s because they tend to hunt in packs, colloquially—and horrifyingly—referred to as “tick bombs.”

“When you find one,” says Holly Gaff, PhD, a professor of biological sciences at Old Dominion University in Norfolk, Va., “you usually make, I always jokingly say, 500 new best friends crawling up your leg.”

Lone star ticks aren’t the greatest driver of tick-borne disease in the U.S.—that distinction belongs to blacklegged ticks, which spread Lyme disease. (Lyme is by far the most common infection you can get from a tick bite in this country.) And though a bite from a lone star tick is less likely to result in disease than a bite from a blacklegged tick, lone star ticks do cause a diverse array of health problems, transmitting bacteria and viruses and also potentially triggering an enigmatic allergy to red meat.

Lone star ticks used to be found mostly in the Southeastern U.S., but they are on the move—and their numbers are growing. They’re becoming more and more common in northern states, and even parts of Canada, where they were once scarce.

“Lone star ticks, once they become established, they become much more common than blacklegged ticks,” says Andrea Egizi, PhD, a research scientist who runs the tick-borne disease laboratory of the Monmouth County Division of Mosquito Control in New Brunswick, N.J. And of all the ticks that commonly bite humans, experts consider lone star ticks the most aggressive species around. You’re a lot more likely to be bitten by a lone star than a blacklegged tick in areas where they’re both common.

Here’s what you need to know about this increasingly common species of tick.

What Can Happen if a Lone Star Tick Bites You?

Bacterial Infection
Lone star ticks are the main vector for a few types of bacteria that can cause the disease ehrlichiosis. The Centers for Disease Control and Prevention usually receives reports of more than a thousand cases of ehrlichiosis each year, with a record of more than 2,000 cases reported in 2019.

Although that’s likely a significant underestimate of the true number of cases, it’s unclear to what extent people may experience asymptomatic or mild cases of the disease. Mild cases of ehrlichiosis resemble a number of other tick-borne diseases, causing symptoms such as fever, headache, muscle ache, nausea and vomiting, and rash, which is more common in children than in adults.

The antibiotic doxycycline, which is also used to treat Lyme, can be very effective. But if treatment is delayed, ehrlichiosis can be serious. Late-stage problems can include damage to the brain or nervous system, respiratory failure, and organ damage. In about 1 percent of cases, ehrlichiosis can be fatal.

Lone star ticks are also one of several tick species that can transmit the bacteria that cause tularemia, another quite rare but potentially fatal illness. Another disease transmitted by lone stars, called southern tick-associated rash illness (or STARI), resembles Lyme disease, but its cause—whether a bacteria or something else—is actually still unknown.

Viral Infection
Lone star ticks are thought to be the primary vector of an emerging tick-borne virus, Heartland virus. About 60 cases of Heartland virus had been documented as of 2022, mainly in Midwestern and Southern states, according to the CDC. A few of those cases have been fatal, says Gonzalo Vazquez-Prokopec, PhD, an associate professor in the department of environmental sciences at Emory University in Atlanta, who studies lone star ticks and Heartland virus.

It’s totally unknown, however, how many people may be experiencing mild or asymptomatic illness due to undetected Heartland virus. That’s in part because testing for the pathogen isn’t available anywhere except the CDC. So testing generally occurs only if a doctor thinks you may have it—which may occur only if other standard treatment for tick-borne diseases (such as doxycycline) proves ineffective.

One of the key mysteries Vazquez-Prokopec and other researchers are trying to solve is which animals are the “reservoir” for Heartland virus—essentially, the animal from which lone star ticks pick up the pathogen and go on to spread it to humans. With Lyme disease, for example, white-footed mice serve as the reservoir in nature, and knowing this helps researchers predict how the disease will spread.

Meat Allergy
This may be the lone-star-induced health problem you’re most familiar with, as awareness of it has spread in recent years. Scientists aren’t sure why, but in some cases, a bite from a lone star tick can trigger an allergy to a protein in red meat, called alpha-gal. (Not everyone who receives a bite from a lone star tick will develop the allergy, and it’s also not clear whether alpha-gal allergy can be caused by triggers other than a tick bite.)

Alpha-gal allergy can be difficult to diagnose because unlike essentially every other allergy, the reaction can be delayed by several hours after eating red meat. And though different people who develop the allergy will experience different levels of sensitivity to the protein, alpha-gal can also be found in other products made from mammals, including dairy products, gelatin, and even some medications. This can add to the difficulty of pinpointing the cause of a reaction.

Where Lone Star Ticks Are Spreading

Lone star ticks have long been firmly established in the Southeastern U.S. In recent decades, however, their numbers have been increasing in Midwestern and Northeastern states. Between 2017 and 2021, according to CDC data, nearly half of reported ehrlichiosis cases were in five states: Arkansas, Missouri, New York, North Carolina, and Tennessee.

Even in some areas where blacklegged ticks are more widely known (and feared), lone star ticks may now be more common. In New Jersey, for example, people who submitted ticks for identification in Monmouth County between 2006 and 2016 were much more likely to send in lone star ticks than blacklegged ticks, according to a study Egizi published in the journal PLOS One. And other research shows lone star ticks have also exploded in population in areas of Delaware, New York, Connecticut, and more.

Some scientists explain this expansion in terms of climate change: A warming climate is making larger swaths of the northern U.S. more hospitable to lone star ticks. That may be part of it. But more recent research suggests that lone star ticks may, in fact, be reestablishing themselves in high numbers in areas where they were once common, before forests were clear-cut for agriculture in the 19th century. According to Egizi’s research, early naturalists recorded frequent sightings of lone star ticks in the late 18th and early 19th centuries, which suggests that they were common at that time in parts of New York, New Jersey, and Pennsylvania—before largely disappearing from these areas.

Deer, the main source of food for lone star ticks, are likely a major player in this story. Deer populations plunged in areas where forests were largely eliminated, but they made a comeback in the 20th century as some former farms became forested again. It seems the deer brought lone star ticks with them.

How to Protect Yourself From Lone Star Ticks

One of the first words entomologists tend to use when talking about lone star ticks is “aggressive.”

Unlike blacklegged ticks, which often perch themselves on a tall blade of grass or branch and wait to hitch a ride as you pass by, lone star ticks will actively chase you down. Suppose you sit down on the ground for a picnic in a lone star tick area, Old Dominion’s Gaff says: Lone star ticks, sensing the carbon dioxide you’re emitting, will crawl across the ground to reach you.

Thus, when you’re in lone star tick territory, it’s important to take precautions to keep them from biting you. As with other tick species, applying an effective insect repellent to any exposed skin is an important measure.

Another very useful anti-tick measure is to wear clothing treated with the insecticide permethrin. Gaff says she is particularly careful to treat her shoes with permethrin because ticks often crawl upward from the ground, so treated shoes can be a barrier to reaching your skin.

Unfortunately, when it comes to keeping lone star ticks out of a place like your yard, we know a lot less about what will be effective than we do with, say, blacklegged ticks. Still, some measures can help. Keeping your grass mowed and your lawn tidy and free of leaf litter is wise. And if you can fence your property to keep deer out, that’s also useful.

Certain measures that can help reduce blacklegged tick numbers definitely won’t help with lone stars, though, Gaff says, and that’s anything that’s aimed at targeting ticks on mice. Lone star ticks generally don’t feed on mice, so measures like tick tubes, which contain insecticide-treated material that mice take to their nests, won’t make any difference on lone star tick populations.

Finally, pesticides that can be sprayed as a barrier around the edge of your yard will help reduce numbers of lone star and other types of ticks. But these are measures to try and avoid, if you can, because these chemicals can also harm beneficial insects.

If you do find a tick crawling on your skin or get bitten by one, it can be difficult to figure out which kind it is. There’s a lot of overlap between lone star tick and blacklegged tick habitats. And while the markings on adult female ticks of the two species are different enough that you might be able to distinguish between them, the smaller nymphs and larvae can be much harder to identify.

If you notice a large number of tiny ticks crawling on you at the same time, though, those are likely to be lone stars. Holly Gaff has a hack for that: When she’s in tick territory, she carries a lint roller, which she can use to pull off a whole lot of tick larvae at a time. (Read more about how to remove a tick, how quickly a bite can make you sick, and what to do if you think you have a tick-borne illness.)

Even if you don’t notice any ticks on you while you’re out in their territory, it’s still smart to take precautions to prevent bites once you get home. Take a shower as soon as you get home. Unlike mosquitoes, which land and bite quickly, ticks tend to take their time crawling around on your skin in order to find a place to bite. Taking a shower is a good way to wash away any ticks that haven’t attached themselves yet, and it also gives you an opportunity to do a thorough check for any bites.

“A lot of people who have ticks right in their backyard may not want to put on a repellent every time they go outside, but they should definitely incorporate tick checks in their daily routine,” Egizi says.