Feature

The Truth about Ticks in Winter

By Blake Dinius, Entomologist, Plymouth County, Massachusetts

Being cool for millennia.

Deer ticks (Ixodes scapularis) have been surviving cold winters for thousands of years. One study estimates expansion into New Jersey around 50,000 years ago. With the northernmost population having survived the glacial maximum along the Mid-Atlantic region, they expanded outward into the Northeast. Winters up here are nothing new to them.

Winter: Just a part of life.

Deer ticks undergo a two-year life cycle from egg to adult. This means thriving in cold weather is just part of their natural development. Every spring, eggs are laid. These eggs hatch into larval ticks, which are active during the summer months. After feeding once on a small animal, these larvae molt into nymphs.

These nymphal ticks will not feed for another eight months or so. Instead, most will survive their first winter as unfed nymphs. Nymph emergence peaks around May and June. However, it’s not uncommon to find them much earlier. Significantly, nymphs pose the greatest risk to humans, being both small and capable of spreading many diseases. Like larvae, they will feed once before molting and will not feed again for several months.

The adult stage is the final stage. Adults become active in the fall of that year. They remain active into the following spring. This means this is the second time ticks will experience winter conditions. Unlike the nymphs, adults are active and searching for a large mammal. Generally, this means they are looking for deer, but a human, cat, or dog will suffice.

Any time temperatures are above 32°F, deer ticks can be active. However, they are a bit sluggish until you get around 40°F and up.

The cold never bothered them anyway.

Deer ticks have several adaptations and behaviors they use to tolerate cold temperatures. They synthesize an antifreeze compound called glycerol. Glycerol lowers the temperature at which water inside the tick freezes. This mitigates lethal cold injury, even as ponds and lakes freeze over. Interestingly, Borrelia burgdoferi, the bacteria responsible for Lyme disease, is thought to use glycerol as a carbohydrate source for survival.

Deer ticks aren’t impervious to cold temperatures, though. If exposed to ~10-14°F or lower for a sustained period, they can die.

But ticks have another trick up their sleeves. They will burrow under leaves and snow. Surprisingly, leaf and snow cover work very well as insulation. Don’t go by what the weather forecast says, you would need to know the local temperature underneath everything to see how ticks are impacted. Even if air temperatures drop to well below zero, temperatures could easily remain in the 20s underneath leaves and snow. I would not expect that last cold spell to impact anything you do to prevent tick bites. Additionally, some data shared at the Annual Meeting of the Society of Integrative and Comparative Biology suggests that deer ticks infected with Borrelia burgdoferi could be more resilient to winter temperatures.

Don’t adjust your thinking about ticks based on the weather!

Treat this time of year like any other time of year.

• Apply tick and flea prevention.

• Perform tick checks after going outside.

• Check your pets for ticks after they come indoors.

• Be cautious around piled leaves along yard edges and alongside trails.

• Clear away snow and leaves from your yard.

• Compromise: If looking to promote habitat by “leaving the leaves,” only clear leaves from the parts of your yard you expect to use often.

Republished from UMass Hort Notes Vol. 34:1