Lyme disease and land use

By Linda Felaco

Tick populations have been soaring this year thanks to the unusually mild winter that allowed more of them to survive. Plus tick populations follow a multiyear cycle in which a drought causes oak trees to produce more acorns, which swells populations of small rodents, which spread tick larvae. So the drought conditions of two years ago are also giving us more ticks this year. A study earlier this year also showed a correlation between increased incidence of Lyme disease and the decline of red foxes, which are very effective at reducing the population of small rodents.

Not only are there more ticks, but last week, researchers at the Centers for Disease Control and Prevention announced the discovery of a brand-new tick-borne pathogen, one of several that have been discovered recently.

Why the sudden emergence of new tick-borne diseases? 

Land use is one factor. From colonial times up until the late 19^th and early 20^th centuries, people converted the forests of New England into farmland, driving out or killing much of the native animal life. Then as agriculture became mechanized, it started moving out west where there was more land in order to take advantage of economies of scale, and many farms here in New England reverted to forest.

So much for Michael Chambers’s thesis about the “irreversibility” of land conversions. But of course anyone who’s ever planted a garden and then neglected to weed it knows how “irreversible” it is.

The edge effect.
(Credit: Nicholas, Wikimedia Commons)

But as the farms reverted to forest, they were now interspersed with dense human settlements, creating what is called “edge habitat.” The animals that survive best in these edge habitats then came to predominate. And those animals just happen to be the ones that best spread ticks, namely deer and mice. Dense populations of deer—whose only natural predator other than humans, namely wolves, are long gone from these parts—and mice have made fertile breeding grounds for ticks and the pathogens that tag along for a ride.

So what’s the solution to the tick problem? Obviously, no one wants to reintroduce wolves to keep the deer population in check. Barring that, land conversions do a good job of getting rid of ticks. Ticks don’t live in the nice suburban lawns of subdivisions; they live in leaf litter on the forest floor.

But shh, don’t tell Ruth Platner I said that …