You’ve probably got spring tick season covered. Pants tucked in, DEET applied, tick check before bed. But if you’re letting your guard down when the leaves start to turn, the data says you may want to reconsider.
New research from the Marshfield Clinic Research Institute’s Tick Inventory via Citizen Science (TICS) program found that deer ticks are significantly more likely to carry Lyme disease in October than in spring — and most people have no idea.
Spring vs. Fall: The Numbers
Researchers tested 707 adult female deer ticks submitted by citizen scientists in 2024. Overall, 51% carried Borrelia burgdorferi, the bacteria responsible for Lyme disease. But the monthly breakdown tells a more important story.
In April, 36% of tested ticks carried B. burgdorferi, in May, 48%, and in October, 66%.
Fewer deer ticks are active in fall than in spring. The ones that are, however, appear far more likely to be infected. One hypothesis: B. burgdorferi may be less able to survive the long winter between tick feedings, so fall ticks that have recently fed are more likely to have picked up the pathogen from a host.
The TICS study also confirmed a consistent second peak in deer tick activity each October, in both 2024 and 2025. The fall tick season is real — it’s just not on many people’s radar.
(Full results are available from the TICS research team at Marshfield Clinic Research Institute here.)
It’s Not Just Lyme
The same deer ticks carry multiple pathogens. The TICS study found that 14% of tested specimens carried more than one — a clinically relevant finding for anyone who sees patients after tick exposure.
Positivity rates across all tested 2024 specimens:
- A. phagocytophilum (anaplasmosis): 9%
- B. microti (babesiosis): 9%
- E. muris eauclairensis (ehrlichiosis, upper Midwest variant): 3%
Ticks carrying Lyme were also statistically more likely to carry B. microti and E. muris eauclairensis. A patient presenting after a fall tick bite may be dealing with more than one infection — and not all of them respond to the same treatment.
For those who want to get into the methodology, a preprint of the full study is available.
Who Needs to Know This
Hunters heading into the woods during Wisconsin’s fall seasons. Hikers who stay active through October and November. Outdoor workers and land managers who stopped thinking about tick precautions when summer ended. The TICS researchers specifically flagged the overlap between the fall deer tick peak and hunting season as a public health concern that hasn’t gotten enough attention.
The Same Precautions. Just Longer.
Nothing about fall tick prevention is new or complicated. Long pants, tall socks, DEET or permethrin, a thorough tick check after time outdoors, and clothes in the dryer on high heat for 10 minutes. The only thing that needs to change is the calendar. Don’t put the bug spray away in September.
Learn more at Tick Academy
These are exactly the kinds of findings — and questions — that Tick Academy is designed to dig into.
IPM Institute’s two-day virtual event returns Oct. 14-15, bringing together researchers, educators, public health professionals, veterinarians, pest management experts, and citizen scientists. Day one focuses on veterinary topics; day two on management and outreach. This year’s keynote speakers are Dr. Jean Tsao and Dr. Nick Ogden, with student research sessions rounding out the program.
