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Winter is an appropriate time to bring up the subject of winter ticks on moose. Many people in this area are aware that this tick species can be a significant, and sometimes fatal, problem for moose. The sight of a heavily infested moose in late winter with large areas devoid of hair is unpleasant. The full impact of the problem is not realized until one gets to see one up very close (usually because it is now dead). Often, the bare patches are completely covered with engorged ticks with no space between them. I have known some folks who could not force themselves to take a second look.
Most of the information in this column comes from the book “White as a Ghost” written by Dr. Bill Samuel (University of Alberta) who is the authority on winter ticks. This species is different than most other ticks in a couple of ways. Most ticks climb aboard their host in spring or summer and drop off when engorged before winter. Winter ticks climb aboard their host in fall and drop off in spring. All tick species hatch from eggs laid by a female and go through 3 stages: larvae, nymph, and adult. All 3 require a meal of blood from a host before going to the next stage. Most ticks take these meals from different hosts, but the winter tick feeds only on the same individual animal for all three meals.
A quick run through of the winter tick life cycle. Engorged females drop off the host in March and April. Engorged ticks have great difficulty walking so lay their eggs very near where they land. Eggs are laid in June and hatch in August- September. In September and October, the larvae climb vegetation to an average height above ground of about 49 inches (or as high as they can if the vegetation is shorter). This is about chest height of deer and shoulder height of moose and then they form clumps of many larvae. When a host walks by and touches a clump, they lock together, and the entire clump goes onto the host animal. During October and November, they feed and moult to the nymph stage. In January through March the nymphs feed and moult into adults. The adults then begin feeding, become engorged, and the cycle is repeated.
I should add a couple of side notes here. I, and a number of others, apparently have brushed against some of these clumps of larvae and suddenly found hundreds of the little beasts crawling around on us. Fortunately, we are not suitable hosts, so just brush them off. Also, in early winter I have occasionally heard someone say they saw a moose and it did not have any ticks. This is because they were still in the nymph stage and were very small. One must part the hairs for a close examination of the body in order to see them.
The bites of winter ticks (at all life stages) cause irritation and itch. The more ticks involved, the greater the itch. Moose attempt to relieve the itch by licking and use of the front teeth, scratching with the hind hooves, and rubbing against trees and shrubs. In severe infestations this grooming behavior eventually leads to breaking of the guard hairs. The hair appears to be dark, but closer to the skin it is whitish-grey. When most of the hair has been broken, the animal appears rather ghostly; hence the term “white as a ghost”. The animal then is referred to as a “Ghost Moose”. If all hair is removed from an area, bare skin is exposed and additional rubbing results in skin damage (leathery appearance, dried blood). This may look serious, but the areas heal with no permanent damage.
The loss of insulating hair and exposure of bare skin means the animal must utilize stored body fat sooner than usual in order to maintain its body temperature. In mild winters this is not a major problem, but in severe winters it could be serious, especially for calves. Calves store very little fat compared to older moose and need to keep growing throughout the winter. This lack of energy reserves can be fatal for heavily infested calves with significant hair loss during exceptionally cold and late springs.
A more serious problem for moose is anemia due to significant blood loss to the ticks and can be fatal. I examined quite a few moose presumed to have died because of winter ticks. I only had the opportunity to examine one soon enough after death to get a good blood sample. It had collapsed and died in a person’s yard as he was having coffee with a friend, and he called me immediately. The blood hemoglobin level was only 3.3, rather than a normal level in the mid to upper teens. The lab tech who ran the sample said a human with that level would not have the strength to get out of bed.
To compound the problem of blood loss to many thousands of ticks on a moose, these ticks consume far more blood than is necessary to become engorged. The excess blood is excreted undigested in their feces and is very noticeable when looking at bare, or nearly so, patches of hide. This, too, adds to the unpleasantness of looking at heavily infested moose.
Moose must replace the blood lost to winter ticks to avoid anemia. Most moose can do this unless the infestation is very severe, but it can be especially difficult (sometimes impossible) for calves. During moose die-offs from winter ticks, most of the deaths are calves.
Next time: Part 2. History of winter ticks, estimating tick numbers, behavioral strategies to avoid ticks, and managing winter ticks.
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