Last week, an article appeared in the Science Section of the New York Times exploring the decline in the moose population in many sections of North America. While several potential causes for this widespread die-off were cited, much attention was given to the role of the winter tick in impacting the health and well being of this large, hoofed mammal.
As a rule, ticks are not considered to be a serious problem in the Adirondacks, especially in the more mountainous areas of the Park. However, the thought of a devastating tick infestation developing across our region is unsettling to outdoor enthusiasts that prefer to hike, camp and explore when the weather is cool.
Like the wood tick and deer tick, the winter tick is an arachnid that has evolved a parasitic existence. Yet, unlike many of its blood-sucking relatives, the winter tick lies dormant for much of the summer and does not become active until the weather cools with the approach of autumn.
The winter tick’s life cycle begins in mid to late spring when it emerges from an egg deposited on the ground, usually along a forest edge or on the side of a commonly used game trail. The larva tends to retreat into a sheltered spot for most of the summer, where it enters an inactive period of its life. During the final weeks of the season, this tiny pin-head size arachnid, becomes active again, along with dozen to hundreds of other larvae that also emerge in the same area, and begin to climb the stems, shoots and trunks of nearby plants. These creatures then cluster on the outermost sections of twigs, buds and needles positioned 4 to 6 feet above the ground. When a passing moose brushes against one of these clusters, the tick larvae immediately transfers onto the fur of its new host.
Since a moose travels great distances in early autumn as it searches for a potential breeding partner, the likelihood of coming into contact with a cluster of winter ticks is far greater than at any other time of the year. Also, the winter tick further increases the odds of an encounter with a moose by locating along a forest edge or a section of terrain likely used by a wandering moose. Additionally, the height above the ground that this parasite chooses to sit and wait for a passing animal targets the long-legged moose over other denizens of the north.
Once a cluster of winter ticks brushes against the side of a moose, they immediately transfer onto the fur and burrow into the dense hair, eventually attaching themselves to the skin. Even though the temperature of the air may not be above freezing, once against the warm body of a moose, the ticks are able to become active and begin feasting on the warm blood of this woodland giant. Although a single tick does not extract much blood, many thousands can adversely affect the health of a moose, especially a young animal.
After living on the hide of a moose for the entire winter, the tick matures, mates and drops off as the moose is returning to its summer range during mid spring. Once on the ground, the female tick deposits her cluster of eggs, which can number well into the hundreds, and the cycle begins again.
It is strongly suspected by some wildlife biologists that the weather during the spring is critical to the survival rate of the eggs. If conditions are cold and rainy, or snowy, many of the female ticks perish or are washed far enough away from a place commonly frequented by a moose. This greatly reduces the chances of a cluster of larvae encountering a moose when autumn comes. Mild, dry weather during mid spring is considered to be ideal for the success of the female and her hatching larvae.
Similarly, cool periods with heavy rains and wind during early autumn can seriously interfere with the ability of tick clusters to remain in place on the ends of twigs. Warm, dry weather is viewed by tick specialists to be perfect for transferring to a host.
While the end of May and June was a cold and dismal period this year, the preceding weeks in early May and much of April were both warm and dry. This was ideal weather for the winter tick to drop off a moose and establish a safe retreat until late summer. Also the prolonged spell of “Indian summer” that the Adirondacks recently experienced has been perfect for tick propagation.
Our region has had several beautiful autumns over the past few years. This weather has been great for tourism, any type of outdoor recreation, and for winter tick success, much to the dismay of our developing moose population.
It should be stressed that winter ticks are specially adapted for parasitizing moose. Deer have evolved the ability to function in areas infested with ticks and are not as negatively affected by them as a moose. While winter ticks may get on a person’s clothing, they often are unable to penetrate the fabric to reach skin. Also, the winter tick is not known to carry any disease that can impact a human.
It is still good, however, to check for ticks even after a hike at this time of year. It is not known how extensive the distribution of winter ticks are in the Adirondacks, but if our moose numbers are also declining, so should the number of winter ticks here in the Adirondacks.
Photo: A moose calf suffering from tick infestation. Photo courtesy the University of Minnesota.