Hunting for an Answer

Can culling deer reduce the growing public health threat posed by disease-bearing ticks in suburban woodlands?

Daniel Horowitz

This fall, for the first time in living memory, Weston, Mass., opened some of its public land to hunting. With the blessing of town officials, skilled archers outfitted in “tree moss” camo apparel and equipped with the latest carbon-fiber bows clambered up into strategically placed tree stands.

Their target was white-tailed deer. One goal of the hunt: Combating one of modern suburbia’s greatest public health scourges. Deer are the preferred breeding ground of the black-legged tick, which is the primary vector of New England’s tick-borne microbes, notably the bacterium that causes Lyme disease.

Weston is only the latest in a string of Mass­achusetts towns to start a deer season bow hunt. Dover, Medfield, Sudbury and Andover have invited in the archers, too, and other towns are considering doing so, causing a quiet renaissance of hunting in thickly settled towns on Boston’s outskirts. But will the tick-fighting strategy prove effective — and safe?

Over its three-decade march through the Northeast and beyond, Lyme has become the most common vector-borne disease in the United States. As its geographic range spreads, the wily pinhead-sized tick has turned once-pleasurable escapes in suburban woodlands — even suburban backyards — into potential rendezvous with serious illness.

The Lyme bacterium is only the most common of New England’s three tick-borne microbes. Local naturalists, dog walkers and woodland hikers have learned to pronounce two other tongue-twisting names: human granulocytic anaplasmosis (HGA), also bacterial, and babesiosis, an illness caused by a malaria-like protist that invades red-blood cells.

This complex web of pathogens, vectors and hosts is verging now on Brandeis’ doorstep, with deer occasionally spotted in Sachar Woods. How close is the hunt? The patch of Weston forest known as the Sears Land, newly opened to bow hunting, is located just a little over one mile west, as the crow flies, from Chapels Pond.

For many observers, active deer management cannot happen soon enough. Ticks are so abundant in some New England forests that even the most careful of woodsmen can acquire a tick-borne disease. Brian Donahue, an associate professor of American studies at Brandeis and an environmental historian, became a case in point last spring when he contracted HGA and spent three days in the hospital recovering.

Donahue is a member of Weston’s conservation commission, which approved his town’s controlled hunt. But not all disease ecologists believe that culling deer in this way can reduce tick-borne illness. And some local residents remain uneasy about sharing the woods with hunters, or express revulsion at killing defenseless deer.

The hunting program is not just about curbing disease, say proponents. Deer-vehicle collisions pose a growing public safety problem in Weston, and deer also threaten the health of town forests. With their natural predators gone and hunting on private land difficult, rising numbers of deer browse forests hard, making way for invasive species. Preserving forest health means protecting wildflowers and ensuring there are enough tree seedlings to replace the losses of mature oaks and maples to windstorms and other factors.

Sudbury, which has about a decade of experience with regulated bow hunting, claims improved forest health and has had no hunting-related incidents. Weston expects to see similar benefits to vegetation — at the same level of public safety.

Thanks to Donahue; his colleague Dan Perlman, associate professor of biology; and lecturer and field researcher Emily Silver ’08, Weston is better prepared than most to verify any vegetation change. The ecologists have set up more than 100 long-term monitoring plots in six of Weston’s conservation areas (you can track their progress at

Vegetation aside, bow-hunt boosters in Weston, as in other Massachusetts towns, also hope to protect human health. In fact, Dover’s health department, not its conservation commission, led the fight to initiate that town’s bow hunt.

Some towns report evidence that deer control does translate into disease control. Crane Beach in Ipswich and Great Island in West Yarmouth recorded lower rates of disease following sharp reductions indeer numbers.

Overall, though, the data on deer and tick numbers are decidedly mixed. Richard Ostfeld at the Cary Institute of Ecosystem Studies, in Millbrook, N.Y., is the most vocal of the disease ecologists skeptical that deer hunts reduce disease risk in any significant way. Though he agrees that cases like Great Island are impressive, he points out that these are places where deer numbers were lowered dramatically, an outcome — in Ostfeld’s view — that controlled bow hunts are not likely to achieve.

Monhegan Island, Maine, offers an extreme snapshot: When its deer were completely eradicated over just a couple of years, black-legged ticks soon disappeared as well. Ostfeld and colleagues agree deer and tick numbers are related, but not in a simple way: There appears to be a threshold effect. Suburban bow hunts, with hunters restricted (at least initially) to small areas of a town’s few large forest fragments, probably can’t reduce the deer herd enough to make a difference in tick numbers. Forest health should improve, and deer-vehicle collisions will likely decline. But the microbe-tick-deer links in the suburban ecological web may prove stubbornly difficult to budge.

Tick and disease expert Sam Telford of Tufts’ Cummings School of Veterinary Medicine is more optimistic about bow hunts, and says that long-term studies are needed to finally resolve this debate. Luckily, biologists have a clever way to monitor ticks. A bright white “flag” of strong fabric, held open by a dowel, is dragged trailside on a rope. The ticks that grab on can be counted, collected and even tested in the lab for the presence of pathogens.

Gathering a large sample of ticks is tedious work, so, as an ecologist with a particular interest in arthropods, I saw a chance to be useful. Last summer — along trails proposed by Donahue, and under the mentorship of Telford — I practiced my tick-dragging skills in Weston’s forests. In the early fall, I taught the 18 students in my field biology class to tick drag as well.

Collectively, our sampling effort this year and over the next several years should provide a tick-abundance baseline for Weston, in the very locations where hunting will take place for many years. Telford believes it will take 10 years to conclusively test how effectively deer hunting reduces tick numbers.

Fortunately, I have found tick dragging to be surprisingly satisfying, especially the long quiet spells required to carefully inspect every inch of white cloth and tweezer off any hangers-on. As dusk settles at the end of a late-afternoon collection — sometimes while the call of a barred or a screech owl entertains me — I turn on my headlamp and get the last clinging ticks secured in my alcohol vials.

A pleasant way to fill some summer days over the next decade — if I don’t get a terrible disease first.

Eric Olson is an entomologist and senior lecturer in ecology at the Heller School for Social Policy and Management.