The cycle of Lyme disease. A diverse array of species affects the prevalence of the bacterium that causes Lyme disease. The cycle begins when ticks attach themselves to infected rodents and become infected with the bacterium. After they drop from the rodents, they molt into nymphs and spend the winter under leaves. In the spring the nymphs attach themselves to hosts again and then drop and molt into adults. As adults, most ticks attach themselves to deer, search for mates, and then lay eggs. During years of high acorn production by oak trees, there is an abundance of food for rodents that produces large rodent populations. Large rodent populations lead to large tick populations that can infect a variety of animals including deer and humans.