Blacklegged ticks, also known as deer ticks, spread the bacteria that causes Lyme disease in the Northeastern, mid-Atlantic and North Central states. Along the North Pacific Coast, the western blacklegged tick, spreads the bacteria that causes Lyme disease. Ticks bite year-round but are most active during spring and summer (April-September.)
While adult ticks are the size of a sesame seed, immature or nymphal ticks are tiny and only the size of a poppy seed. Most humans are infected with the bacteria that causes Lyme disease through nymphal ticks, which are harder to see.