The bacterium that causes Lyme disease is a master of disguise, changing its appearance to evade the immune system as it moves from the ticks that carry it to humans or animals.
Black-legged ticks carry Lyme disease, which continues to spread widely across the United States.
CDC/Michael Levin
Reforestation and reintroduced deer populations are helping ticks expand their range. The parasites bring the bacteria that causes Lyme disease with them.
Middlebury Assistant Professor David Allen prepares to inspect a piece of canvas dragged through the forest to collect ticks.
Todd Balfour/Middlebury College
Ticks are generally inactive in the winter and start to look for their next meal as temperatures warm up. But as winters warm, every season may become tick season.