Blacklegged ticks are prospering in Minnesota.
In just a few decades, the blood-sucking arachnids have spread to almost all forested areas of the state. So has Lyme disease, which the ticks carry.
The arrival of spring — a prime time to find adult blacklegged ticks, otherwise known as deer ticks — has brought Minnesota Department of Health epidemiologist Dave Neitzel to Rice Creek Chain of Lakes Park Reserve in the northern Twin Cities metro. It's an urban forest loaded with ferns, raspberry bushes and hazel.
"Let me take just a little exploratory drag through here," says Neitzel as he collects specimens from the forest floor.
Dressed in white painter's coveralls with duct tape wrapped tightly around his ankles, Neitzel drags a white canvas cloth across the ground. Fabric strips weighted with fishing sinkers dangle from the end of the cloth. This design allows some of the fabric to slip through the underbrush to the leaf litter below. That's where blacklegged ticks spend most of their lives.
"I've got a female for sure," Neitzel says, as he prepares to place the tick in a vial. Females have a distinctive reddish- orange band at the tail end of their dark brown bodies. The tick is hard to see even on the white canvas. It's about the size of a sesame seed.
Neitzel was one of the first public health biologists in the country to study these ticks in their natural environment.
"It is a cause that I've championed," he says. "I don't think you can understand vector-borne disease risk unless you see what's going on out in the field and kind of pair that up with what's being reported from physicians, the cases that are being reported."
Neitzel's years of field research have helped clarify the tick's habitat. Years ago, some of his peers assumed the ticks could be found in grassy areas. But Neitzel's research showed that blacklegged ticks prefer the humidity of the forest floor. They'll venture to the edge of the woods, but not much beyond.
Minnesota's changing forest environment has been a boon for the blacklegged tick. Timber harvesting has spawned younger forests with more vegetation growing at ground level. That's good for the ticks, and for deer and mice — two primary hosts for the ticks.
People have also changed their recreational habits, drawing them much closer to the ticks. Back in the '80s very few people rode ATVs through wooded areas. Now that's just one of many recreational activities that occur regularly in forests.
"Kids that play paintball in the woods, that's something that people never did before, but now they do," Neitzel says.
Winters have also been milder, reducing the number of ticks that die off. But even an exceptionally bitter winter is no longer enough to stop the unprecedented movement of the ticks. That's because there's strength in numbers. A single female can lay a couple thousand eggs.
The blacklegged tick's success story has become a growing public health threat for people. Minnesota has as many as 1,500 annual Lyme disease cases now, compared to 200 in the 90s.
"Lyme disease cases showing up where we never saw Lyme disease before," Neitzel says.
Jenny Erickson was visiting the park the same day as Neitzel. She's painfully familiar with blacklegged ticks. She got Lyme disease last summer.
"I never found the tick on me, but I got the bullseye," she says, referring to the distinctive rash left on the skin by ticks.
Neitzel suspects she was probably bitten by a blacklegged nymph. The immature ticks are a third of the size of the adults, which makes them almost impossible to see.
Erickson's symptoms appeared last August, just a few weeks after peak nymph activity. It takes a few weeks for Lyme disease symptoms to develop. Nine months later she's still not back to full health.
"I have a ton of joint pain and fatigue," she says. "There was a point where I need to get help getting out of bed and stuff like that."
Reducing the number of Lyme disease cases is a top priority for public health officials. But so far there are no easy ways to control ticks. Spraying pesticides isn't very effective: It's hard for the chemical to reach the ticks where they live deep in the leaf litter.
Current research is focused more on finding ways to keep the pests off the animal hosts. But those control methods are expensive.
While that research continues, Neitzel says his best advice is to wear protective clothes and repellents in wooded areas. And he'll keep tracking the expansion of the ticks' range, so people know where they are.
This spring blacklegged ticks have again turned up in a new location, having been discovered as far west as New Ulm.
"I know that they know not what they do," Neitzel says. "They're just out there trying to feed and reproduce and there's not much thought that they have. But what impresses me is how successful they can be."