Predators may not be "controlling" Lyme Disease as some thought


When it comes to predator management in North America, the last decade has proven tumultuous and riddled with stark debate. Especially when discussing the management (regulated hunting and trapping) of canid species like wolves, coyotes, and fox - it isn’t long before heavy discourse arises over the “proper” way to manage wildlife.

For example, it has been debated for decades that coyotes shouldn’t be managed by humans at all. Special interest groups like the Humane Society of the United States have long rallied for elimination of coyote management based on the theory that they “manage themselves” through a process dubbed “responsive reproduction”. As I discovered after researching modern coyote management concepts at the beginning of the year, the sciences behind concepts like “responsive reproduction” are far from what gets spun into newspaper editorials and political inboxes - there’s two sides to every story. Don’t forget that fact.

Fox management has also been recently scrutinized by environmental protectionists in the Northeast, particularly in New Hampshire and Vermont, which I also researched and reported on.

And of course, lest we forget New Hampshire’s ever-so-popular and controversial “bobcat season proposal” from a few years ago. Predator management across North America has been, and will continue to be a debatable hot-button topic.

The latest trend in controversy over predator management in the Northeast appears to be the relationship between predatory species and rodent control. More specifically, the control of Lyme Disease vectors such as white-footed-mice and chipmunks.

The argument is pretty self-explanatory. Some feel as though state game agencies shouldn’t be supporting the regulated harvest of predators such as foxes and coyotes, since the more predators gorging on mice, the less mice there will be to carry Lyme infecting ticks, thus slowing the spread of Lyme disease, and by proxy, the contraction of Lyme to humans.

But as any good researcher knows, the wild kingdom will seldom play by such black and white rules. Which is probably why biologists at Vermont’s Fish & Wildlife Department decided to do the “scientific thing” and investigate further. After animal rights activists petitioned Vermont F&W in 2018 demanding an immediate closure on all measurable fox management (hunting and trapping), the Department released their findings in a study titled “Fox & Lyme Disease - Is There A Connection In Vermont?

The State’s Findings

Vermont’s findings were pretty much as I had long suspected. Nature is far too complex to conclude that foxes and other canids are somehow on a higher plane of existence than other wildlife. My big take-away’s from the report:

  1. Forces influencing the increase of black-legged tick (Ixodes sacpularis) and Lyme disease in the region are incredibly complex, and can’t be pinned on just one factor (like predatory control of mice).

  2. There are other, seemingly more pressing factors that regulate populations of vector rodents like mice and chipmunks. Factors that impact these animals, for example habitat change, weather and food abundance, can also have an impact on human Lyme disease trends.

  3. Alternate factors, such as climate and invasive plants, may harbor and influence Lyme-carrying ticks more profoundly than merely “hitching a ride” on host mammals.

  4. Food availability, as stated above, will play a key role in rodent abundance. Nature goes through cyclical “boom and bust” mast production years. When food (such as acorns) are produced in excess, rodent populations will increase. When food is low, rodent populations weaken. These grand cycles take place regardless of predatory impact.

  5. To suggest that predatory species such as fox and bobcats feed primarily on mice is taking quite a big leap of faith. The reality - wild animals are opportunistic. They feed on what’s available. Voles, shrews, rats, mice, muskrats, woodchucks, birds, trash, plants, insects, roadkill, squirrels, each-other… there’s no golden rule to survival. Additionally, very few predators will put in the effort to stalk and chase down, say, chipmunks, when more “sluggish” prey is readily available. Yes - foxes and other meso predators eat mice, but they eat a lot of other stuff too.

You can view Vermont’s Red Fox & Lyme Disease study in its entirety below. I encourage you to do so, as the study is packed with tons of useful information which can’t be covered in one single column.

And What of Other Predators?

During New Hampshire’s fox season debates, many opposed to management techniques (in the form of regulated hunting and trapping) bolstered the same “hands-off” approach to predator management. The message was similar - eliminate regulated seasons on predators like fox and fisher and allow those populations to (hopefully) wipe-out Lyme vectors “in their own natural way”.

The same argument regarding foxes has been used by many in the anti-hunting camps to establish a stance for abolishing the regulated hunting and management of eastern coyotes - yet, some studies suggest coyotes don’t seem to impact Lyme vectors as efficiently.

More so, Eastern coyotes directly compete with red foxes for territory. As do bobcats with fisher. In theory, holding one or two predatory species in hierarchy over other meso predators further down the food chain would seem to contradict the notion that a perceived “end” to hunting and trapping of predators will “solve” a supposed prey abundance problem. For example, if foxes are believed to be efficient at reducing rodent populations, why would we then also cease regulated management of the Eastern Coyote, which is known to kill and/or “drive” red foxes out of territories where Lyme vectors may be prevalent.

In New Hampshire’s case, those opposed to fox hunting and trapping stated in public record that the Fish & Game Departments must “trust their biologists”. In Vermont’s case, those biologists did their homework. Vermont’s biologists go on to state and conclude:

“The VFWD manages and conserves Vermont’s wildlife species in trust for the people of Vermont. This includes the varied public interests in Vermont’s wildlife, as well as, ways to address public health, safety, and quality of life. For this reason, the VFWD has conducted this in-depth evaluation of the various environmental factors influencing the presence and prevalence of Lyme disease in the state.

After a thorough review of the petition’s concern regarding the influence of Vermont’s fox harvest on the prevalence of Lyme disease in the state, the VFWD can find no compelling evidence that the current rate of harvest of foxes is influencing the presence, distribution, or prevalence of infected black-legged tick nymphs, the primary driver of Lyme disease.”

They say water is good for your health. Too much water however, is toxic, and can lead to death. North America’s predators are great - but they aren’t Gods. Both top and meso predators alike should be regarded as a key component of wild ecology, but also require the same conservation management as other wild species.

conservation doesn’t stop at lyme

The basic life cycle of a three host tick.

Wild canids aren’t the only ones subject to Lyme control sensationalism. There’s little argument that North American opossums are good at eating ticks as well as insects. They’ve been equated to the “Hoover Vacuums” of tick consumption. Some studies boast that possums will consume around 90 percent of ticks they encounter. The only catch I was able to find - these figures are based on ticks that attach to the possum, which are consumed during grooming, rather than possums actively seeking out ticks on the forest floor. I also had a hard time tracking down any concrete information that dictates what impacts this has on the actual spread of Lyme disease, however I think we can all agree a dead tick is a good tick.

Not long ago, I was heavily criticized in newspaper editorials by local anti-hunting “eccentrics” for my publishing of a pro-possum-trapping article. I was accused of “promoting” the spread of Lyme disease in humans by trapping surplus possums (even when it came to wildlife control measures, such as removing invasive families of possums from Ms. Peterson’s basement crawlspace). In my article, I talked about the sustainable use of the resource, and I even laid out several immense benefits possums provide the ecosystem and society - and I still couldn’t make some people happy! I received this criticism despite the fact that, for all the benefits possums provide, they also carry a host of health issues. Los Angeles is one of several cities currently feeling the brunt of a possum-induced Typhus Fever outbreak.

Possums clearly aren’t as proficient with their flea removal as they are with ticks - being a big contender in the pest control industry for introducing fleas into suburban dwellings. According to New Hampshire records, the possum is one of the top nuisance wildlife control complaints in the state - topping in around 80% in 2017.

Then of course there’s also their transmission of Equine Protozoal Myeloencephalitis, leptospirosis, tuberculosis, relapsing fever, tularemia, spotted fever, toxoplasmosis, coccidiosis, and trichomoniasis - just to name a few.


My point - furbearers like possums are great! They’re beneficial, welcomed guests for many across North America… in moderation. The same can be said for meso predators like foxes and fisher. With regulated management in play, the hope is that these species can thrive while also being scientifically managed to ensure healthy coexistence with humans and other species of wildlife. Overabundance of these predators translates to disease outbreaks (such as rabies, sarcoptic mange, and distemper), and the potential negative detriment on other wild species (such as ground nesting birds and endangered species). Their role in tick control shouldn’t overshadow other important aspects of ecology and conservation.

After all, there is such a concept as “too much of a good thing”.

Read more on Furbearer Conservation’s predator management reports: