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Nymphs questing through the forest. The phrase conjures up images of a scene from “Game of Thrones.” But encountering a real nymph on its quest offers a potentially harmful brush with climate change.

Immature deer ticks are called questing nymphs. They now inhabit a wide swath of North American forests, but they didn’t always. During early summer, their quest is for blood. The season now starts earlier and lasts longer than it did in the past, which is good for the ticks. But it’s bad for humans, because these ticks carry the bacteria, viruses, and parasites that cause Lyme disease, anaplasmosis, deer tick encephalitis, and babesiosis.

I have collected thousands of nymphs as part of my dissertation research on the invasion of Lyme disease across North America. I’ve witnessed along the way that where these ticks thrive has been heavily influenced by humans.


Deer tick invasion

Encounters with ticks didn’t always cast a dark shadow over North American summers. Cases of Lyme disease first appeared in 1976 in the woodsy suburb of Lyme, Connecticut. At that time, deer ticks were found only in a hotbed encircling Long Island Sound, along with a small area in Wisconsin.

Since the 1970s, deer ticks have rapidly extended their reach north, west, and south. The most recent map shows that deer ticks now roam throughout the eastern coastal states, from Maine to Florida, and across the Midwest. They are now established in 45 percent of US counties. That means the deer tick has more than doubled its reach in the 20 years since the previous map was published.


The spread of Lyme disease has closely followed the spread of the forest nymphs. Lyme disease is now the most common disease transmitted by a vector — a mosquito, tick, or other bug — in United States. More than 30,000 cases are reported each year, and the Centers for Disease Control and Prevention estimates that 10 times as many Americans develop the disease.

Regions where ticks that carry Lyme are established (red) or reported (blue).
Regions where ticks that carry Lyme are established (red) or reported (blue). Alex Hogan/STAT

In part, ticks are following the spread of one of their favorite sources of blood: deer. As deer populations exploded over the last sixty years, thanks to strict hunting laws and the largely predator-free and deer-friendly landscapes in New England and the Midwest, deer ticks followed. However, the steady crawl of ticks north into Canada can’t be explained by deer alone.

Ticks spend the majority of their lives on the forest floor. They are vulnerable to changing local climates and death by freezing, drowning, or desiccation. Warmer winters and longer summers let more ticks survive and thrive further north each year. Warmer temperatures quicken the tick life cycle, too. Tick eggs hatch sooner and ticks spend more time questing for blood, and so are increasingly likely to feast on a human and pass on a disease-causing pathogen. Because more ticks survive and mature more quickly, diseases can be transmitted faster.

Species that thrive under climate change

The barriers we have created — the heated, cooled, and (somewhat) bug-free spaces we inhabit — give us an artificial sense of immunity to the disturbances shaking our fragile ecosystems. Nymphs don’t respect the barriers of urbanization and wealth that protect many Americans from vector-borne diseases. Window screens, socks, and our skin don’t stop the invasion of nymphs, reminding us of our vulnerability to ecological changes brought about by climate change, habitat fragmentation, and deforestation.

As we worry about the ability of some species to run from climate change and escape extinction, ticks, mosquitoes, kissing bugs, and the parasites they carry may thrive under climate change. Where will these crawling and flying disease carriers move? And who will be at risk for what were once called tropical diseases?

The consequences of climate change will vary dramatically across the globe and are difficult to predict. The yellow fever mosquito (which also carries dengue, Zika, and chikungunya viruses), for instance, is predicted to spread rapidly in some areas, including eastern North America and large parts of southeast Asia, and become less common in others areas, like much of Australia.

A changing climate will affect mosquito-borne diseases in subtler ways, too. In a warmer climate, the dengue virus matures more quickly (up to a certain temperature). That means an infected mosquito can more swiftly spread the virus.

The consequences of climate change will be felt most profoundly by people living in or near areas where diseases carried by mosquitoes and other vectors are already common, and where poverty makes it difficult to stamp out these diseases.

A forest nymph brushing against a hiker doesn’t begin to drink blood immediately. She crawls across the skin, searching for a comfortable dinner spot. She grips her prey with spindly legs and uses knife-like mouthparts to slice into human skin. She secretes cement around the wound, binding herself to her host, and then begins to imbibe. Once attached, this offspring of a changing climate can’t be simply brushed off.

Katharine Walter is a graduate student in the Department of Epidemiology of Microbial Diseases at Yale University.

  • or… Plum Island. The coincidences are way too many and they were working with several tickborne illnesses, and conducting experiments using ticks- native and non-native, as well as infecting deer. Several outbreaks right around that time and Lyme disease is right smack in the middle. A federal investigation uncovered serious flaws in the containment procedures and the laboratories containment system was installed improperly pushing air out when it was supposed to be keeping it in! You can see all the research in this timeline with many documents and the plum island research journals

  • In another article, Katharine Walter also attempted to blame Lyme Disease on climate change. She wrote, “climate change has been warming our winters, accelerating ticks’ life cycles and extending their range eight miles farther north each year.”

    That is nonsense.

    In the first place, the idea that tick-borne diseases prefer warmer climates is implausible on its face, because Lyme and Rocky Mountain Spotted Fever were both first encountered in cold States with harsh winters: Lyme, Connecticut for Lyme Disease, and northern Idaho & Montana for Rocky Mountain Spotted Fever.

    In the second place, even if the ticks which carry those diseases were not well acclimated to cold climates, global warming is not shifting climate zones by eight miles per year, nor even at 1/10 that rate.

    From this climate/hardiness zone map you can see that 1°C (1.8°F) of warming is roughly equivalent to a shift of about 50-60 miles south, in the United States:

    The rate of global warming over the last few decades has been only about 0.01°C per year, which is equivalent to a shift of about 1/2 mile south, not eight miles.

  • I would highly recommend that the deer tick (black legged tick) not be the only tick recognized as the main culprit of Lyme disease transmission. If you study the Lone star tick you will see that this tick is a hunter!! It’s fast moving and will track it’s pray down just as well as the black legged deer tick. I find it very hard to believe that a tick can have B. Burgdorferi enter its body yet it can’t transmit it? Please, can anyone lead me to any scientific studies showing the lone stAr tick is capable of taking In this bacteria, attach itself to a host or its prey yet the bacteria can’t be transmitted back out from where it came from (the ticks gut) and infect the host it has attached to. It makes absolute no sence to me at all. How is it that the black legged deer tick, mosquitoes and other insects can or possibly can transmit Lyme disease (B. Burgdorferi bacteria) yet the Lone star tick which is a blood hunting tick that will seek any warm blooded animal like humans,mice, deer and anything else it can attach itself to, yet they the CDC says the Lone Star Tick can’t transmit it. I want to see the data that proves this because the Lone Star tick does carry the B. Burgdorferi bacteria. I know this as fact and I can prove this myself. Also I would like to know why so much effort and billions of dollars is being spent on this zika virus yet the Lyme disease and coinfections seems to be under treated,Misdiagnosed and the only people that can get long term treatment are rich, wealthy people. The tests that most insurance companies cover are so insensitive and they were made this way for what reason? The places that do have more sensitive tests are very expensive and are not covered by most if any insurance companies and not FDA approved. If a doctor who specializes in Lyme disease (which isn’t covered by most if any insurance companies does diagnoses his or her patient with lyme disease the cost of treatment is still not covered and I am talking about the cost for more then the “standard treatment” which is now known only to be affective if the infection is caught early. Johns Hopkins research has verified that if its not treated IMMEDIATLY then the 30 days of one single kind of antibiotic might treat the symptoms for a while but in a lot of patients it does not cure the infection. Also the tests look for antibodies. It is now known that this Lyme bacteria and other bacteria and viruses actually suppress ones immune system so if your given An antibody test which is very insensitive there is a great chance it comes back false negative. Then your told its all In Your head. It’s unbelievable to say the least. How much longer do we sufferers sit back and take this BS. Yeah, get with a support group they say. For what? I am sick, I don’t want a support group, I want to get well so I can move on with my life. How about just coming up with an accurate test that actually is reliable so it can be detected and treated as soon as possible so the insurance companies can pay for this as they should, but don’t ! It’s despicable and makes me sick to my stomach thinking they will only cover the “standard treatment” which is known to be in effective in people who didn’t get the treatment as soon as they pull the tick off of their body. How can anyone say for sure how long a tick has been attached to them. The standard treatment should be if you are bitten by a tick and you literally pull the tick off your body, for one, SAVE THE TICK, the get it tested and be treated IMMEDIATLY no matter if there is this bullseye rash or not. This seems like the best bet even if you have to pay out of your pocket because it will be a lot cheaper to pay for two months of antibiotics rather then waiting and having to pay for years of treatment out of pocket, and possibly be disabled. This is a crime against humanity as far as I am concerned. One more thing, climate change has nothing to do with the Lyme disease epidemic and the corrupt CDC, government and insurance companies. If 300,000 are being infected per year when do all the support groups get together and do something besides talk! When is the 1 million patient March going to be held? I don’t want pity, I want to be well so I can contribute to society again! Is Something wrong with that? Let’s figure this out first then we can talk about this climate change because this epidemic isn’t changing for the better anytime soon unless something is done now and fast!!! It’s very frustrating to talk in circles when WE KNOW WHATS GOING ON!!! God bless everyone and shame on you CDC, government, and insurance companies that do not cover treatments that are needed. One day you will have to answer for YOUR Lack of action!! I hope it’s sooner then later too and I am speaking for all the people with this Illness. What a shamed!!!

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