Low-Lyme Landscape: It’s the trees, not the ticks
If you spend a lot of time outdoors, like I do, you’re more or less perpetually alarmed about Lyme disease. Even more alarming are the array of other tick-borne diseases that are way scarier, but reported at much lower levels — SO FAR!! As always, it’s easy to panic, and difficult to know what to do.
Those rare-but-scary other diseases make solutions that only work on Lyme, like vaccinations, only so promising. More promising are solutions targeting these diseases’ common factor: what people are doing, what ticks are doing, and where they meet each other.
There’s some surprising tidbits to be found in this. Like this: most people are infected with Lyme in their own yards, during daily activities, not out in the woods on that hike or camping trip. Maybe this is because we think about ticks in the woods but we don’t at home. Or perhaps people who choose to be out in the woods are people more likely to know about ticks and take those precautions — you were wearing special hiking clothes anyway — while people doing daily activities in their yards are just people, without that self-selection effect.
You can’t stay in the house forever, so can you de-tick your yard or de-Lyme your ticks? Another surprising fact: deer aren’t the main villains here. The tick in question is the deer tick (aka blacklegged tick), so white-tailed deer get blamed for this modern plague. But a closer look at the life cycle of Lyme-infected ticks reveals the key middleman is much smaller and more common: the white-footed mouse. As mice tend to be, they are around in large numbers, unnoticed, and closer than you think. You see deer, but not mice. This particular mouse likes woodsy areas and their edges. Your yard will do fine, especially if you live in a heavily wooded area like much of New England, ground zero for Lyme.
It’s tough to exclude mice from your yard. You can fence out deer, but just try fencing out mice. What really works to suppress mice is eating them. Since you probably don’t want to try that yourself, it’s lucky that foxes are very happy to do that job. A 2017 study found that indeed, where there are more foxes (and some other European predators, where the study was set), there are lower numbers of Lyme-infected ticks and ticks in general. Surprising again, the key dynamic in play seemed to be that mice move around less when there are predators around, as the study’s authors speculated. There are still mice around, but they are kept under wraps by the foxes, so they encounter fewer ticks.
Red foxes are champion mouse eaters, and where foxes are, there tend to be other creatures. Some of these, like opossums and possibly turkeys, eat a lot of ticks, which helps in a different way. Others could help in a less direct but effective way by serving as alternate hosts for ticks. This means the ticks bite other creatures, like squirrels, that are less likely to carry Lyme disease instead of disease-carrying white-footed mice, and therefore never become infected with Lyme. You may still get bitten, but you won’t get infected if the tick that bites you doesn’t carry Lyme.
How do you get foxes on board in your backyard fight against tick-borne disease? You do it with landscape management, looking at your yard and neighborhood as habitat. This starts with trees. A landscape with very small patches of forest is good for mice, but not larger animals that prey on them or on ticks. A landscape with larger patches of forest has the potential to house foxes and possums and so on, thus keeping the lid on mice and ticks and Lyme. In urban areas, tree canopy is often referred to as the critical factor in the presence of foxes and other larger wildlife. It stands to reason, though, that what’s under those trees matters, too, as well as what kind of trees they are. More diverse woodlands with greater diversity of plants at ground level, especially native plants, tend to be home to greater diversity of wildlife.
What else makes up the low-Lyme landscape? At a more detailed level, it’s less obvious what’s good and bad. Leaf litter is the natural cover of the forest floor, but it’s also habitat for deer tick nymphs and larvae. Brush and tall grass create good wildlife cover, but they are also the preferred spots for adult ticks to lie in wait for someone to bite. Every creature needs a water source, but dampness and humidity are key to deer tick survival. Obviously there are a series of trade-offs here that merit more study to discover the right balance. Foxes in particular need den sites, hollow logs or buildings to dig under or similar. But these same denning sites can also make the fox’s larger cousin, the coyote, at home, which brings us to one last surprising fact.
Where there are coyotes, there are fewer foxes, because the bigger, stronger coyotes tend to kill the foxes. So if more foxes means less Lyme, do more coyotes mean fewer foxes and therefore more Lyme? That’s exactly the suspicion of a few researchers studying the matter, who note that the key factor in the outbreak of Lyme in New England may have been the arrival and establishment of coyotes in the region.
So stay tuned, but consider what a low-Lyme landscape might be. Maybe also consider what the fox is worth to you that keeps you from getting Lyme disease, and what the forest that nurtures that fox is worth, too. The assortment of creatures living around us and the web of their interactions with each other plays a surprisingly key role here. You can surround yourself entirely with pavement and buildings. You can do the vegetated version of that with closely mown, chemical-soaked lawn. Or you can have a diverse, intact woodland edge ecosystem that works just well enough to allow predators like foxes to keep the mice and their ticks in balance, without making coyotes too much at home. Wild, but not too wild; just wild enough.
This post is a preview of a sidebar in my upcoming book about the neglected city, Design by Deficit. For more like this, check out my blog City Wild.