April 28, 2017

Killing Deer to Kill “Deer” Ticks

I was reading George Smith’s article about how the Maine Department of Inland Fisheries and Wildlife (MDIFW) is making plans within their proposals to draft 15-year management plans for deer, to figure out how the state can manage a “socially acceptable” population of deer and at the same time mitigate the affects of Lyme disease, at a socially acceptable level. Lyme disease is believed by most to be carried by the deer and thus deer have become the target. Because the deer is the target, the controversy comes from three different entities – those who find deer cute and cuddly and want them running all about their land; those who want them available in ample supply to hunt and fill their freezers; those who hate hunters and are willing to kill deer so hunters can’t enjoy their sport.

It certainly does appear that reducing deer populations (to what level I’m not sure there is a standard number due to varying influences and environmental factors) will reduce incidences of man contracting Lyme disease.

The life cycle of the tick responsible for carrying the infectious disease, including all directly influencing factors, is complicated. Perhaps the deer has become the easy target due to a lack of understanding about how to interrupt the life cycle of the tick – more appropriately should be called the mouse tick.

The deer is a host.  This means that an adult tick hitches a ride on a deer for the purpose of obtaining a meal of blood. This is all a necessary part of the life cycle. It is not the deer, however that gives the disease to the tick. The tick does infect the deer, but studies have shown that a deer will “cleanse” itself of the disease and thus is not considered a carrier of the disease.

It’s the white-footed mouse that is the main culprit of transmitting the disease. Once infected, the mouse remains a carrying until death. After the tick leaves the deer, the female ticks hatch all new larvae. The larvae make their way to the mouse, where the Lyme disease is passed to the nymph. As I understand the cycle, the tick larvae cannot have the infection but pick it up from the mouse as it becomes a nymph. The infected nymph grows to an adult and begins looking for a host for another blood meal.

Incidentally, the larvae doesn’t only go to the mouse. It can travel to other rodents and small wildlife, where the disease can be passed to the nymph, which can become an adult tick and begin looking for a blood meal.

It would appear that any interruption or change of this cycle would limit or change the prevalence of the tick. One way that has been tried is to reduce the populations of deer. In places where deer populations are very dense, a serious thinning of the herd becomes a reasonable limitation to tick growth and prevalence. It would only make sense…wouldn’t it?

Have we looked enough at finding ways to control the white-footed mouse? Snakes, owls, bobcats, weasels, and foxes are common predators. Are there changes in these predators and their environment that are effecting the white-footed mouse? Short of the use of chemicals, is the “natural” way of keeping mice in check being interrupted some how? Are changes in our ecosystems increasing, decreasing or having no effect on the perpetuation of the tick and Lyme disease?

Modeling in recent years has suggested that perhaps those predators that readily find the white-footed mouse a prey species, have been reduced in numbers to where they are ineffective at any kind of control over the mouse. There are a couple of difficulties in this presentation. First, to my knowledge, the modeling has not been taken to the field, or, if it has, results have not been made public. Another issue is that “scientists” can’t even agree on what predators consider the mouse’s prey. Some say the fox is the biggest predator of the mouse and some say the coyote is. Some say that even though the list of natural predators of the mouse is varied, there is little interruption of the perpetuation of mice.

I would find it interesting that it appears that the incidence of Lyme disease has increased right along with the prevalence of coyotes. If coyotes regularly eat white-footed mice for lunch, wouldn’t it make some sense that this would tend to reduce the prevalence of the spread of Lyme disease?

The argument is also made that the presence of coyotes limits the number of foxes, therefore, fewer mice are eaten. The theory has been laid on the table that coyotes do eat mice, but live in a more spread out habitat than the fox and so the effective result is that fewer mice get eaten, thus more ticks and more disease. Consider also that, for those familiar with the boots-on-the-ground eating habits of the coyote, an animal that will eat anything, the diet of the coyote includes “snakes, owls, bobcats, weasels, foxes and probably any other creature that, given the opportunity, would feast on a white-footed mouse.

So, depending upon which bandwagon best fits your narrative, will determine whether you want to kill deer, mice, or coyotes. For the MDIFW, their job will, more than likely, end up being a matter of making deer management decisions based on social demands rather than good science. But this is nothing new.

But above all,

DON’T GO LOOK!