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In part 1, I only covered the life cycle of winter ticks and their impact on moose. Part 2 will present additional important information on them. Winter ticks are not found in Alaska, Newfoundland or northern most Canada. Other than those areas, all North American moose populations have winter ticks. Their primary hosts are moose, elk, white-tailed deer, mule deer, and woodland caribou. However, they can also infest many other large mammals both wild and domestic.
The winter tick was first described in 1869 and there were reports of winter ticks causing problems for moose the same year. The first reported die-off’s of moose because of winter ticks were in Saskatchewan in 1916; then another in 1921- 1922 when many horses and cattle also died. In 1923 there was a reported moose die-off from winter ticks in Minnesota. During the 1930’s there were numerous reports of dead moose due to winter ticks from most of the Canadian provinces and several U.S. states. They have continued ever since.
The 1991, there was a major moose die-off due to winter ticks in northeastern Minnesota. During March of that year, 46% of moose observed had noticeable hair loss due to ticks. So many dead tick infested moose were found by wildlife managers, foresters, and local citizens that the northeastern Minnesota moose hunt was cancelled.
So how many ticks are on moose? A considerable amount of work has been done to be able to get good estimates of that. First, a reliable technique had to be developed so one did not have to try counting every tick on every moose to be examined. Twenty moose hides were cut in half to yield a left side and a right side. The half hides were laid flat and cut into 10 cm X 10 cm squares and numbered as to its location on the hide. Each square was then placed in a separate jar with heated potassium hydroxide (to dissolve the hair and hide, but not the ticks) and a small amount of liquid detergent (to disperse any fat clumps). Then each jar was poured through a small sieve to obtain the ticks so they could be counted. This was very time-consuming work, and it took several days to do each half hide.
Once they had determined the number of ticks on each patch of hide for each half hide they could calculate the tick density on each half hide (average number of ticks per square centimeter). Next, they had to determine how many 10cmX10cm samples were needed to yield a good estimate of that tick density. This too took time, but they determined that a random sample of 15% of a half hide was needed to give an accurate estimate. From tick density and the surface area of that hide, they could then estimate the total number of ticks on an animal. Although it was a lot of work to develop the technique, it has saved tremendous hours of work that would have been needed to obtain good tick estimates for the several hundred moose hides which have been examined.
As an example of tick infestation on moose, Dr. Samuel listed results from 214 moose hides from western Canada. The average number of ticks per moose was about 33,000, 19% had over 50,000, 6% had over 80,000, and 3% had over 100,000 ticks. A calf with 50,000 ticks had 20 ticks per square inch. Two very heavily infested moose were a bull with 150,000 ticks (37 ticks per square inch) and a calf with 145,000 ticks (50 ticks per square inch).
There are a few defenses against ticks. Although grooming can damage the hair, it does remove many ticks. Magpies, ravens, and gray jays sometimes feed on ticks on the backs of moose. The most interesting defense is that apparently moose can avoid (at least some) clumps of larvae on vegetation. This was demonstrated with a captive cow moose. Two identical pails of alfalfa pellets were placed in an outdoor pen. Several clumps of winter tick larvae were put in one of the pails. The cow had been infested with ticks the year before so had experienced tick bites. She always ate from the pail with no tick larvae and avoided the pail with tick larvae.
How can we help reduce winter tick abundance? One suggestion is to burn them. Engorged females often drop off when a moose beds in open to semi-open areas that are grassy and the larvae stay in those same spots. Fire (either natural or prescribed) may be effective in killing ticks and larvae if used in spring and/or fall, but actually treats little acreage. Another approach is to manage moose numbers to keep their numbers from becoming so high that tick populations explode and saturate the habitat. Moose then become infested with unusually high numbers of ticks and the result is a moose die-off. The more moose, the more ticks. The appropriate moose population level will depend on each situation and is not easily determined.
Weather is the most effective control of winter tick abundance. If winter lasts well into spring and the engorged females land on snow, they will likely die in a few to several days. Cold weather can also result in fewer eggs being laid. Cold weather during summer and fall can kill larvae, especially during early snow storms. Larvae that do not find a host die when the weather gets cold. Moose are very well adapted to cold weather. Ticks not on a host are not.
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