If you spend time in the Northeast outdoors, you’ll want to stock up on strong insect repellent this year.

According to an article on NPR.org, researchers are expecting a surge of Lyme disease cases in the Northeast in 2017. They are basing that prediction on a surge in mice populations in the region last year.

Mice serve as a kind of early warning system for Lyme disease. Researchers say the number of critters scampering around the forest in the summer correlates to the Lyme cases the following summer.

The explanation is simple: Mice are highly efficient transmitters of Lyme. They infect up to 95 percent of ticks that feed on them. Mice are responsible for infecting the majority of ticks carrying Lyme in the Northeast. And ticks love mice; an individual mouse might have 50, 60, even 100 ticks covering its ears and face.

So that mouse plague last year means there is going to be a Lyme plague this year.

Read more about researchers expecting an increase in Lyme disease in the Northeast in 2017.