Black-legged Ticks

This marks the 20th anniversary of my column for the Pennsylvania Game News. The first appeared in January 1993 and concerned the Carolina wren. Thanks for reading!
—Marcia

Last January I walked along the Black Gum Trail. Since our son, Dave, constructed the trail halfway up Laurel Ridge, back in the 1990s, I had never been able to take the trail in winter. Usually, it was deep in ice and snow as was our north-facing hollow road. But on that mild day there was not a smidgeon of ice or snow on the trail or road.

I neither saw nor heard any creature despite the warm day. The long-promised sun was trying to shine through a matrix of puffy, white clouds drifting past patches of blue sky. At dawn it had been 34 degrees and breezy, and the thermometer had been slowly rising all morning.

Then, as I descended the trail, I glanced down at my pants and socks and pulled off seven adult black-legged ticks. I could hardly believe it. I had considered winter to be tick-free on our mountain. Usually, they spend their winters buried under leaf litter that should be covered with snow. But they are tough creatures, and as soon as it warms up they are out and about. At that time the adult females are not carrying Lyme disease because they had had their last blood feeding on white-tailed deer. Some even winter on the deer.

But, as Dr. Richard S. Ostfeld of the Cary Institute of Ecosystem Studies in Millbrook, New York says, don’t blame deer if you get Lyme disease. The immune system of deer kills the bacteria that cause the disease.

“We don’t know why,” Ostfeld says, “but the deer immune system clears the infection. When they get bit, they wipe out Lyme. Deer play a tremendous role in suppressing adult ticks from spreading the bacteria.” He also dislikes the name “deer tick” and prefers “black-legged tick.”

After all, like any arachnid to which ticks are closely related, the nymphs and adult ticks have eight black legs. But the larvae only have six. The larvae hatch from the several hundred to a few thousand eggs each female adult tick lays in spring. She then dies. Both the larvae the first summer and the nymphs the second summer feed once on a mammal and prefer white-footed mice, although they will feed on other small mammals or birds if they can’t find a mouse.

And it is white-footed mice that are the real culprits. They can get the Lyme disease bacteria and pass it on to the ticks even though the bacteria don’t seem to sicken them. Because nymphs are so small, no larger than a poppy seed, they are liable to bite and never be detected during the three to four days they need to take their blood meal. At least 70% of Lyme disease cases are from those nymphs that do not look like the black and reddish-brown adult female ticks. Instead, they have dark heads and bodies that appear to be translucent. Adult male ticks, which don’t feed but will attach to a host when searching for a female to mate with in the fall, are either black or dark brown.

Entomologist Thomas Say named the black-legged tick — Ixodes scapularis — back in 1821. But the first known case of Lyme disease wasn’t identified until 1975 when several children in Lyme, Connecticut were diagnosed with juvenile rheumatoid arthritis. It turned out to be what later was named Lyme disease. In 1982 scientist Willy Burgdorfer isolated the bacterium causing the disease, and it was named in his honor Borrelia burgdorferi.

Scientists also thought that a new species of tick carried the disease and named it Ixodes dammini. It was only later in the 1990s that they realized the tick transmitting the disease had been around and named long ago. But they did recognize that the tick belonged to the family Ixodidae, the so-called hard ticks. They have a hardened plate called a scutum on their idiosoma region, which is a specialized part of a tick’s body that expands to hold its blood meal.

Like ticks everywhere, the nymphs and adults climb a shrub or blade of grass, hold out their forelimbs, and wait for a victim to brush past. They also lurk on fallen logs, tree trunks, or even on the ground, especially the nymphs which can’t climb as high as the adults. Since they arrived on our mountain, about six years ago, I no longer have the pleasure of sitting on my hot seat on the ground, my back against a tree, watching the life of the forest. They even reach me on our benches unless I pull my feet up on to them.

Ticks have a Haller’s organ on each foreleg with spiny indentation packed with sensors and nerves capable of picking up a breath of carbon dioxide, heat, sweat, or even vibrations from your footsteps. So no bird or mammal can escape their sudden lunge. As I’ve discovered, the small huckleberry shrubs on Laurel Ridge Trail and the grasses of First and Far fields, are ideal “questing” posts for ticks, as well as the underbrush in our forest off the trails where I rarely venture anymore.

Once a tick arrives on its host, it probes around for a soft, bloody site to attack, often in private crevices. Normally, you won’t feel a thing. As David George Haskell writes in The Forest Unseen, “I suspect they charm our nerve endings, taming the cobralike neurons with the hypnotic music of their feet.”

The tick presses its mouthparts into your flesh and saws an opening. Then they lower a barbed tube, called the hypostome, to draw out blood. Because it takes several days to get a full blood meal, it cements itself to your skin with a glue-like material called “attachment cement,” which is why a tick is so difficult to remove.

During the first 24 hours it is attached, it is harmless. But later, when it is full, it takes water from your blood into its gut and spits it back into you, which is when it can transmit Lyme disease or two other diseases — babesiosis and anaplasmosis. The parasite Theileria microti causes babesiosis and Anaplasma phagocytophiolum causes anaplasmosis. As many as 2 to 12% of Lyme disease patients will have anaplasmosis and 2 to 40% babesiosis. This complicates the diagnosis and treatment sometimes because the tick might transmit one or the other or both diseases and not Lyme to a patient. In rural New Jersey, for instance, the Center for Disease Control studied 100 black-legged ticks and discovered that 55 of them had at least one of the three pathogens.

Both babesiosis and anaplasmosis have flu-like symptoms similar to those of Lyme disease but without the telltale bull’s-eye rash. Some folks don’t recognize or even have symptoms of babesiosis, yet they can pass it on to others through donated blood. So far, Pennsylvania seems to be almost free of those two diseases, but they are more prevalent in New York and New Jersey. Unfortunately, it is probably only a matter of time until these diseases increase in the commonwealth.

Last year was supposed to be especially high in Lyme disease cases. That was because in 2010 there was a bumper crop of acorns, followed by 2011 when there were practically none. Dr. Ostfeld, forest ecologist Dr. Charles D. Canham, and colleagues at the Cary Institute first worked out the connection between the amount of acorns and the population size of white-footed mice. In abundant acorn years mice numbers soar but they crash when the acorn crop fails. According to Ostfeld, that leaves a large number of infected ticks looking for hosts. Without the mice, they are after us instead.

At least one hunter friend of ours contracted Lyme disease last June. Although he did get the rash, he never saw the tick. I suspect it was a nymph that bit him. He also listed four places where he could have picked up the tick — turkey-hunting at our place, at a friend’s country property, and on his own country property, or his backyard at the edge of Altoona.

If Ostfeld’s research is right, his backyard was the most likely habitat. In a paper for Conservation Biology Ostfeld and other colleagues entitled “Effect of Forest Fragmentation on Lyme Disease Risk,” they wrote, “Our results suggest that efforts to reduce the risk of Lyme disease should be directed toward decreasing fragmentation of the deciduous forests of the northeastern United States into small patches… The creation of forest fragments of 1-2 hectares should especially be avoided, given that these patches are particularly prone to high densities of white-footed mice, low diversity of vertebrate hosts, and thus higher densities of infected nymphal black-legged ticks.” Given both the size of our forest and the diversity of vertebrate species, we should have less Lyme disease here.

On the other hand, another study by Tom Worthley and other researchers at the University of Connecticut Forest in Storrs claims that eliminating the invasive Japanese barberry shrubs (Berberis thunbergii) will help control the spread of Lyme disease, anaplasmosis, and babesiosis because white-footed mice favor the barberry’s habitat.

“When we measure the presence of ticks carrying the Lyme spirochete we find 120 infected ticks where barberry is not contained, 40 ticks per acre where barberry is contained, and only 10 infected ticks where there is no barberry,” Worthley says.

Unfortunately, our neighbor’s old 100-acre property that we were able to purchase only after it was poorly logged, is filled with Japanese barberry and other invasives. It’s also moved into the edges of our fields and even into the edge of portions of our older forest. Eliminating all of these bushes will take many manpower hours. But our caretaker hopes to experiment with a few of his own ideas for removing them over the next several years.

In the meantime, I’ll continue to follow most of the suggestions for avoiding tick bites, including super vigilance of my clothes and body, even in winter, when I take my daily walks.