Those of you who plan to be out and about in the woods or in other ways communing with nature this summer, be careful: experts are anticipating a heightened alert for Lyme disease. No one is completely certain why, but there has been a recent study on the subject, and it is a good look at how all the disparate elements of an ecosystem work together. First of all, the ticks that carry Lyme disease are conventionally called “deer ticks,” but are more common living and feeding on mice and other small mammals. Ticks are fruitful and multiply by partaking of a bloodmeal from a suitable host. That is, momma tick lays its eggs, larvae hatch, and, in order to—ahem—keep on ticking, need to be fed with blood from a host, usually a mammal. And thus the larvae progress through the next two stages: nymph and, finally, adult tick. Where Lyme disease comes in is via the bacterium Borrelia burgdorferi, and the species name does not imply that it was first identified in Bergdorf Goodman. Anyway, normally, tick larvae are free of this microbe, but when the bloodmeals they receive do contain it, the nymphs the larvae grow into become Lyme carriers. These nymphs need another bloodmeal to make it to the third stage, adult tick. If they bite another mammal, B. burgdorferi then infects a new host. Sometimes that mammal is a human, which how we get the disease. (Deer, it turns out, have been acquitted of guilt in Lyme disease because their systems can expel the bacterium pretty quickly. Smaller mammals like mice do not expel it at all. So Lyme-infected mice are an all-you-can-eat buffet for hungry tick nymphs.) You may be able to see where this is going. What leads to a proliferation of mice? A reduction in mice predators. In this case, the red fox is a primary predator of small rodents. So researchers wanted to track the populations of red foxes in states with the highest prevalence of Lyme disease, and faster than you can say “I’m comin’, Elizabeth!”:
The models showed higher numbers of Lyme disease cases in places where there are fewer foxes. They detected no significant relationship between numbers of deer and numbers of Lyme disease cases.
Why are there fewer foxes? It turns out, more and more coyotes have been moving east and northeast and displacing the foxes and other predators. To recap:
more coyotes equals fewer foxes, which means fewer predators, which means more small animals are running around that could be carrying the bacteria for Lyme disease. More bacteria is therefore transmitted to more ticks, which then transmit the bacteria to humans. It’s complicated.
Also, new coyote-wolf hybrids are taking these large predators to new places, as well. Nothing in nature exists independently of anything else; it’s all an interconnected web of life—and we’re often trapped in it.