Northern “Immigrant” Ticks Causing Concern in the South
Changes in tick behavior may increase Lyme disease risk in regions previously considered lower risk.
Ticks locate hosts through a behavior known as “questing.” According to the CDC, ticks hold onto leaves and grass with their hind legs while extending their front legs outward, waiting to latch onto a passing host. [2]
When a person or animal brushes past, the tick quickly climbs aboard.
Study Examines Tick Behavior in North vs. South
Arsnoe and colleagues compared the questing behavior of nymphal black-legged ticks in Michigan and Tennessee.
Using a simple model—measuring how often ticks climbed a wooden dowel—they found a striking difference:
- Nymphal ticks in Michigan were 8 times more likely to climb
- Ticks in Tennessee showed significantly lower questing behavior
Why Do Southern Ticks Behave Differently?
The authors proposed several explanations:
- Southern ticks may avoid climbing to reduce the risk of drying out (desiccation)
- They may feed on hosts such as skinks below the leaf litter
- They may represent biologically distinct tick populations
These behavioral differences may help explain regional variation in Lyme disease risk.
Emerging Concern: Northern Ticks Moving South
Researchers identified Ixodes scapularis populations infected with Borrelia burgdorferi in eastern Tennessee, suggesting the region may be becoming a transition zone.
If northern ticks—with their more aggressive host-seeking behavior—continue to expand southward, Lyme disease risk could increase in areas where it has historically been lower.
This raises important questions about changing patterns of exposure. Learn more about Lyme disease risk by region and how geography influences infection rates.
Clinical Perspective
In my practice, I advise patients that Lyme disease risk is evolving.
Geographic boundaries are shifting, and behaviors that increase exposure in one region may become relevant in another.
Clinicians and patients alike should remain alert to these changes—particularly in areas previously considered low risk.
References:
- Arsnoe IM, Hickling GJ, Ginsberg HS, McElreath R, Tsao JI. Differences in questing behavior of blacklegged tick nymphs. PLoS One. 2015.
- Centers for Disease Control and Prevention. Tick life cycle and host-seeking behavior.
- Arsnoe I, Tsao JI, Hickling GJ. Nymphal Ixodes scapularis questing behavior explains geographic variation in Lyme borreliosis risk. Ticks Tick Borne Dis. 2019.
Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.
Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention
