Marcia Bonta

naturalist writer

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

Black-legged tick

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.”

three deer in snowy woods

White-tailed deer in Plummer’s Hollow (photo by Dave Bonta)

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.

White-footed Deermouse (Peromyscus leucopus)

White-footed Deermouse (Peromyscus leucopus) by J. N. Stuart (Creative Commons BY-NC-ND license)

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.

Black-legged tick on human skin.

Black-legged tick by Jerry Kirkhart (CC BY license)

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.

Japanese Barberry berries

Berberis thunbergii – Japanese Barberry berries by Virens (CC BY-NC-ND license)

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.

January 1, 2013 Posted by | black-legged tick, Brush Mountain/ Plummer’s Hollow, mice and voles, white-footed mice, white-tailed deer | , , , , , | 10 Comments

Little Loggers

Last winter I spent more time watching meadow voles beneath our feeders than I did birds. The heavy snowfall in early December provided perfect cover for them and when most of it melted later in the month, the voles’ runways were easy to see. Several voles had nests near our feeders and often their dark gray heads poked out of them to grab a seed or two.

One Saturday afternoon I sat at our bow window watching birds while I listened to the Metropolitan Opera radio broadcast, but I ended up being more interested in meadow vole behavior. On that day, they ventured farther from their nests along their open runways to eat birdseed, and I often mistook them for dark-eyed juncos until they moved. By finding and then focusing my binoculars on a nest entrance, I was able to get excellent views of the plump, beady-eyed creatures sitting there, running along their runways, or feeding with gray squirrels, juncos, and mourning doves. The squirrels chased the birds and each other but didn’t seem to see the voles. Maybe that’s because these nervous little engines of energy move incredibly fast. Once I saw two, one right after the other, dive into a nest entrance.

Well into January, I continued my vole watching. Probably there were more than two but only a couple were out at the same time. They would pick up a seed with their front paws and, sitting on their back haunches, eat it much as a squirrel might (they are, after all, both members of the Order Rodentia). The voles used our discarded Christmas tree, along with the tree sparrows, song sparrows, and juncos, as cover when they ventured out to nibble dried and still-green grasses on the periphery of the feeder area. Juncos startled them whenever they flew in or foraged near their nest entrances, and the voles always darted back into their nests. But they also paid attention to the birds’ frequent alarms, and when the birds flew up in a panic, the voles dashed for cover.

After a month of vole-watching, snow and ice once again sealed them off from the outside world, an ideal situation as far as the voles were concerned because they were safe from many of their enemies, especially avian predators such as hawks, owls, blue jays, and crows. Even many of their larger enemies–foxes, opossums, skunks, and feral house cats–would have found it difficult to break through the thick ice layer that covered the foot of snow on our mountain during much of February.

In the meantime, the voles lived in their surface runways beneath the snow, where their other major predator–weasels–could have chased them down, or in their five-to eight-inch-in- diameter, globular-shaped nests of grasses where they huddled together to conserve energy during the coldest days of winter. Most often, such groups consist of juveniles staying with their mothers although occasionally one or two adult males may join them. They also ate the roots, tubers, leaves, seeds, fruits and grasses they had previously cached above and below ground in preparation for winter.

In late February two fifty-degree days quickly melted the icy snow cover, and once again the meadow voles were visible below the feeders as they ran along their open runways. But even more amazing were the immense number of vole runways that meandered through the dried grasses of First Field like the mazes in children’s magazines and activity books. These patches of torn-up, matted grasses that scrolled themselves across the landscape had been painstakingly constructed by the voles’ sharp teeth as they snipped off any green sprout that surfaced. Slightly wider than a garden hose, their previous under-the-snow passageways were now exposed to the sunlight and the eyes of predators. Their many domed, grassy nests were also open to the outside world.Vole runways did not cover all of First Field. Voles particularly like the thick cover of bluegrass and First Field still harbors pockets of it that were planted decades ago so that was where many of the nests and runways were concentrated. They also like moist areas of dense vegetation, made up primarily of grasses and sedges. Both the lower portion of our once-lawn, a former wetland, and a three-acre wetland at the bottom of First Field above the stream, were crisscrossed by vole runways. Along the runways, occasional piles of little, brownish-green pellets marked the voles’ communal toilets.

By late March, the meadow voles had begun breeding as the promiscuous males competed for the attention of promiscuous females. After a gestation period of 21 days, a female has her first of eight or nine litters in a season. Those litters range in size from one to 11, with an average, in Pennsylvania, of five to seven. She is bred almost immediately after bearing a litter and has a mere three weeks to tend her young, which are born blind, pink, hairless, and helpless, before she has another litter.

At one week, the young are already covered with fur and their eyes are open. At two weeks, they are weaned, and the following week they are on their own. The females of a litter can breed at four weeks of age and the males at five. All this breeding makes the meadow vole the most prolific mammal in Pennsylvania. Without a wide variety of predators, they would quickly overrun their habitat, especially every third or fourth year when their numbers are high. Back in 1924, one captive female, observed by Vernon Bailey, a mammalogist for the United States Biological Survey, produced 17 litters in one year and a daughter from her first litter had 13 litters that same year.

The meadow vole, whose scientific name in 1815 was Mus pennsylvanica (Pennsylvania mouse) for its type locality in meadows below Philadelphia, is now Microtus pennsylvanicus or Pennsylvania small ear, referring to the vole’s tiny ears. Also popularly known as the field or meadow mouse, it is no friend of the white-footed mouse of field and forest. When vole numbers are high, mouse numbers are low which may explain why we had no mice in our old farmhouse last year. Researchers aren’t sure how the voles keep mice out, but they suspect that the much larger and more pugnacious voles may attack and chase any mice they find. Certainly, I frequently observed the voles chasing each other from the birdseed.Both mice and voles are a necessary part of the food chain, supplying endless meals for larger creatures. But do they serve other purposes in the natural world?

Ecologist Richard S. Ostfeld and his associates at the Institute of Ecosystem Studies in Millbrook, New York, have been studying the effect mice and voles have on tree regeneration in old fields. He built nine, one-third of an acre enclosures in old fields and filled them with high (400), medium (175), or low (80) densities of voles per two and a half acres. In each enclosure, he planted tree seedlings of species that colonize old fields in the eastern United States and discovered that the high-density voles killed 95 percent of the seedlings, the medium-density 80 percent, and the low-density 65 percent. They showed a definite preference for red maple, white ash, and the invasive tree-of-heaven and disliked white pine and red oak. Even those seedlings that they didn’t eat, they clipped off near ground level, leaving distinctive, diagonally cut stumps. For some reason, which the scientists haven’t figured out, voles like to keep their homeland free of tree seedlings.

A separate study of white-footed mice found that they only ate tree seeds. Between the mice and voles, establishing a forest in an old field seemed almost impossible.

The next enclosures Ostfeld built were at the boundary between forest and field, since trees usually invade old fields at the edge of the forest. He left the forest end of the enclosures open, figuring that the voles would stay in the field and that mice would move between field and forest. Again he established the same densities of voles as the previous set of enclosures and again they ate the same kind and number of tree seedlings. The mice turned up their noses at those species and instead ate the seeds of red oaks and white pines.

Over the years, Ostfeld found that few tree seedlings of any species survived if vole numbers were high and mice numbers low, but many tree seedlings thrived if mice numbers were high and vole numbers low. As an ecologist, Ostfeld was fascinated by the influence of the “little loggers,” as he calls voles, on the natural world.

“These rodents…play a strong role in preserving attractive vistas and maintaining the open habitats favored by such other wildlife as deer, turkeys, woodcocks, and bluebirds,” he wrote in Natural History magazine. “And meadow voles, by excluding white-footed mice from some habitats, may reduce the risk of Lyme disease, which is carried by ticks that feed off (and are infected by) these mice.”

Could that be why we have not, so far, seen a tick on our mountain? Or why the wetter portions of our field have not been invaded by any tree seedlings in the 32 years we have lived here?

Everything is indeed connected to everything else as more than one ecologist has observed. And unraveling those connections remains a daunting task even for scientists. Our fields, after all, are not the fields that Ostfeld studied and our voles and mice may prefer and dislike different tree species.

The complexities of the natural world continue to fascinate me and I have Never Enough of Nature, as the late, great scientist Lawrence Kilham entitled one of his books. Who would have suspected that meadow voles, in addition to providing food for many predatory birds and mammals, could not only control mice numbers but the regeneration of forests?

December 1, 2004 Posted by | Animal Behavior, Biologists in the Field, Brush Mountain/ Plummer’s Hollow, Forest Issues, Grasslands and Barrens, Lyme disease, meadow vole, mice and voles | Leave a Comment

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