What diseases does the deer tick carry?

In Massachusetts the deer tick (blacklegged tick) can transmit Lyme disease, babesiosis, anaplasmosis, and Powassan virus. Lyme is by far the most common. It does not cause alpha-gal syndrome, which is linked to the lone star tick.

When are deer ticks most dangerous?

Nymphs peak in June and July and cause most Lyme cases: they are the size of a poppy seed and easy to miss. Adults have a second peak in the fall and can bite on any day above freezing.

What does a deer tick look like?

Adults are reddish-brown with a solid dark shield (scutum), black legs, and no white markings, roughly the size of a sesame seed. Nymphs are much smaller, about a poppy seed. They have no white dot, which distinguishes them from the lone star tick.

How fast can a deer tick transmit disease?

Lyme transmission usually needs the tick attached for a day or more, so prompt removal helps a lot. Powassan virus, though rare, can transmit within hours, which is why any attached tick should be removed quickly.

The Deer Tick in Massachusetts

The deer tick (Ixodes scapularis), also called the blacklegged tick, is the most important human-biting tick in Massachusetts. It is found statewide and is the carrier of Lyme disease, along with babesiosis, anaplasmosis, and Powassan virus.

Adult deer tick (blacklegged tick) with a dark shield and orange-red body on a blade of grass — Adult deer tick, no white markings. CDC / Jim Gathany (public domain).

Statewide

found across MA

Jun–Jul

nymph peak, riskiest

Lyme

main disease

4 diseases

incl. Powassan

Lyme disease risk by county

Reported Lyme cases per 100,000 people, by Massachusetts county (MA DPH). Barnstable County is highest.

High — 200+ cases per 100k. Cape Cod, the South Coast, and the western hilltowns.

Moderate — 90 to 200 per 100k.

Lower — under 90 per 100k, mostly the dense metro counties.

These are per-capita county rates, so populous counties can read lower even where wooded towns are high-risk. Your town's daily score separates them.

Diseases the deer tick carries

Lyme disease

The most common tick-borne illness in Massachusetts. An expanding “bullseye” rash, fever, fatigue, and joint aches are typical; caught early it is usually treated successfully with antibiotics. Massachusetts has among the highest Lyme rates in the country.

Babesiosis

A malaria-like parasite that infects red blood cells, causing fever, chills, and fatigue. It can be serious for older adults and people without a spleen or with weak immune systems. It is notably common on the islands and Cape.

Anaplasmosis

A bacterial infection bringing fever, headache, chills, and muscle aches, treated with doxycycline. It has risen sharply in Massachusetts, especially in the western counties.

Powassan virus

Rare but serious: it can cause brain swelling (encephalitis) and has no specific treatment. Unlike Lyme, it can transmit within hours of a bite. Still uncommon, but an emerging concern in the Northeast.

How to identify it

Reddish-brown with a solid dark shield, black legs, and no white markings. Adults are about a sesame seed; nymphs are a poppy seed and cause most Lyme.

When it's active

Nymphs peak in June and July; adults have a fall peak and quest on any day above freezing. Risk is lowest in deep winter but never quite zero.

How to protect yourself

Repellent, permethrin-treated clothing, and a tick check after wooded or brushy areas. Prompt removal of an attached tick sharply lowers the chance of Lyme. Not medical advice.

Get your town's deer-tick risk today

TickZone turns weather, the tick life-stage, habitat, and county disease data into one daily 0–100 score for each of the 351 Massachusetts towns.

Check your town →

Frequently asked questions

What diseases does the deer tick carry?: In Massachusetts the deer tick (blacklegged tick) can transmit Lyme disease, babesiosis, anaplasmosis, and Powassan virus. Lyme is by far the most common. It does not cause alpha-gal syndrome, which is linked to the lone star tick.
When are deer ticks most dangerous?: Nymphs peak in June and July and cause most Lyme cases: they are the size of a poppy seed and easy to miss. Adults have a second peak in the fall and can bite on any day above freezing.
What does a deer tick look like?: Adults are reddish-brown with a solid dark shield (scutum), black legs, and no white markings, roughly the size of a sesame seed. Nymphs are much smaller, about a poppy seed. They have no white dot, which distinguishes them from the lone star tick.
How fast can a deer tick transmit disease?: Lyme transmission usually needs the tick attached for a day or more, so prompt removal helps a lot. Powassan virus, though rare, can transmit within hours, which is why any attached tick should be removed quickly.