Ticks: A Sign of Climate Change

By Jenevra Wetmore

It is tick season. Most Vermonters know to spray ourselves with repellant before going out, wear protective clothing, and do regular tick “checks.” This message has become second nature to those of us who spend time outdoors, but it wasn’t always this way. I grew up in Vermont and had a tick-free childhood. Most of us who have lived here since the 1990s can say the same. What happened? Though the full response to this question is more nuanced, the simple answer is: climate change.

Ticks love warm weather, and climate change is making Vermont winters shorter and warmer. Vermont’s average annual temperature has gone up by 2.6 degrees Fahrenheit since 1895, and Vermont winters are warming faster than our summers. Since 1960, summers have been warming by .4 degrees per decade, while winters have been warming by .9 degrees. Rather than be killed off by the cold, ticks are surviving year-round. Ticks are not active when the temperature falls below freezing so, as winters warm, tick activity increases and the season when they are active lengthens. This means more opportunities for humans and other animals to come into contact with them.

There is medical proof of our growing tick problem. In the early 1990s reports of Lyme disease were rare, but Vermont now averages some 600-700 confirmed cases in a year. In 2017, this number ballooned to nearly 1,100 and Vermont had the highest per-capita occurrence of Lyme disease in the nation. 

The blacklegged tick, commonly referred to as the “deer tick,” is responsible for nearly all (99%) of cases of tickborne diseases in Vermont. Unfortunately, humans aren’t the only ones impacted by the rising tick population– among other animals effected, the state’s moose herd is also struggling. The Vermont Fish & Wildlife Department has observed moose so heavily covered with ticks that they are severely underweight from blood loss, with hair rubbed off from scratching. In 2019, about 70% of young moose in a study conducted by Fish and Wildlife had died before they were a year old. Previous years saw deaths closer to half the animals in the study.

When we think about climate change we often think about the possible future effects—rising sea levels, hotter temperatures, and more extreme weather events, to name a few. While these dangers are very real (and happening as you read this column), they can make it easy to miss the effects of climate change that are already here in plain sight. In Vermont, ticks are one of the signs of global warming that we have become somewhat accustomed to, much as we’ve become used to the warming climate and changing weather. Children today will never know a spring walk in Vermont’s woods without ticks.

Climate change is a slow-onset disaster, which is a term used by the United Nations to describe environmental degradation processes such as sea level rise and droughts. “Slow-onset” is not to say that climate change is not dangerous or an imminent threat, but rather to distinguish climate change from rapid-onset disasters such as hurricanes and floods. When Tropical Storm Irene hit our state in 2011, we were able to see the washed out roads, flooded houses, and massive erosion. This was a rapid-onset disaster with an emergency response. It is more difficult to see the larger patterns caused by climate change, including: warmer average temperatures, more intense storms, less snow cover, and shorter winters. We are living in the midst of a climate emergency, but it can be easy to forget. Only when we step back to look at a larger timescale can we fully appreciate the catastrophe that global warming is, and will become. 

Think back to the Vermont of your childhood, or ask elders what changes they have noticed. In addition to ticks and warmer winters, we have already seen the range of some species expand northward, such as the possum–an animal my grandmother never encountered until late in life. Red-bellied woodpeckers and Carolina wrens, once a rare sight, are now common. These are changes I would not have been aware of if not for the elder Vermonters in my life. This will be our role in the future–to act as a living memory of changes in the landscape, and to advocate for policies and daily actions to reduce carbon emissions and mitigate climate change.

Hosts for the blacklegged tick (Ixodes scapularis) include mammals, birds, and reptiles. When feeding, infected ticks transmit the bacterium that causes Lyme disease (Borrelia burgdorferi) to humans and animals. Photo credit: Centers for Disease Control/Jim Gathany.


  • Visit the CDC website for precautions you can take to prevent tick bites and Lyme disease: https://www.cdc.gov/ncezid/dvbd/media/lymedisease.html
  • Become a citizen scientist. Observe and record the changes among plants and animals being caused by climate change. Make your natural history observations count by entering the information into Nature’s Notebook—the online database of the USA National Phenology Network: https://www.usanpn.org/natures_notebook
  • Share your sightings of climate-sensitive bird species in the eBird online platform: https://ebird.org/home.


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