"The Rise of the Tick" by Carl Zimmer

I know some of you may be squeamish about ticks (I am because I have pulled so many off of me), but this is an interesting article on how various host species and predators influence tick populations. For example, although increases in deer numbers due to abandonment of farmland on the East Coast have increased tick populations, a recent study describes that what might have played a larger role were the increases in white-footed mouse numbers due to decline of their fox predators.  The native fox, in turn, used to coexist with wolves in the area until wolves were eradicated and coyotes killed or scared the foxes away.

To throw another player into the mix, the invasive Japanese barberry shrubs taking over Eastern forests are providing a more humid environment to prevent ticks from drying out and greatly increasing their numbers.

I had no idea that black-legged tick populations used to be so limited: "The sheer volume of black-legged ticks in the eastern United States is staggering, but it’s even more mind-blowing when you consider their history. Up until the mid-1900s, biologists found them only at the eastern end of Long Island and a few islands off the coast of Massachusetts."  Lyme disease, which the ticks carry and spread, is now found across most of the U.S. except for the South.

http://www.outsideonline.com/outdoor-adventure/science/Feeding-Frenzy.html?page=all