The Winter Deer Tick (Dermacentor albipictus)

Ectoparasite of the Moose

The winter deer tick is a large tick that feeds on moose in North America. Although closely related to the common wood tick that we find on our dogs and ourselves during the spring and summer, the winter tick leads a very different life style. Unlike the wood ticks, it spends its whole life on one host (a moose or a deer) and is active all winter.

Dermacentor albipictus - Adult Male

To understand the winter tick, we must know something about what scientists call the life cycle. All ticks go through four different life stages during their life cycle: the egg, the larva or newly hatched "baby" stage, the nymph or immature "teenage" stage, and the adult male and female stage. The tick feeds only three times during its life cycle, once during each stage except the egg stage. After the first two feedings, the tick will molt or transform into the next stage. This transformation involves shedding skin, growing larger, and sometimes adding new body parts. For example, the larval tick has six legs but gains two more legs when it becomes a nymph.

The winter tick starts its life as an egg in the spring time under ground litter. One adult female will lay a clump of hundreds of eggs. In three to six weeks the eggs hatch into larval ticks that bunch together and wait until the cold weather of autumn. Once the cold arrives, the larval ticks will climb the nearest plant and wait for a moose to accidentally rub up against them. When a moose comes close, the larval tick becomes very active, waving its forelegs in anticipation of attaching itself to the moose. This process is called questing and depends on a lot of luck and the presence of a moose. Most larval ticks will be unlucky and die because they never make contact with a host. The lucky ones that successfully hitch a ride will crawl down the ladder of hair to the base, then bury their mouth parts into the warm flesh, feasting on the life-giving blood of the moose. After the larva feed, they molt into nymphs. The nymphs will feed and molt into adult male and female ticks. This process takes several weeks.

The adults mate and the female takes her last feed. It is necessary for the female to take a huge meal to provide the nutrition to create hundreds of eggs. This feeding will take several days to complete. The meal is so large that she engorges or bloats to several times her normal size (about the size of a thumb nail). These engorged females will drop off the moose and onto the ground in early spring where they will seek a sheltered area to lay their eggs. Then the life cycle starts all over again.

Ticks seem to prefer the ears, belly, anal region, and under the legs, although they can be found on most other parts. By their feeding actions, ticks physically aggravate the moose. In an attempt to rid themselves of these pesky parasites, a moose will try to rub them off. The number of ticks on an infested moose can be astounding. As the moose keeps rubbing the thick winter hair (which is extremely important in providing insulation against winter's cold), the hair is dislodged. Skin is often left raw and exposed to the elements. Some moose lose all their hair and literally die from exposure (hypothermia) in severe winter weather.

Winter ticks are one of the most important parasites of moose. They are widely distributed in North America and are especially abundant in the northern states and Canada where moose and white-tailed deer coexist. The moose's lack of resistance to this external parasite may indicate it was not exposed to the parasite (as in the case of white-tailed deer) until it came into greater contact with the white-tailed deer when deer moved into the moose's range after the widespread cutting of timber in the boreal forests of North America.

Horses are sometimes severely infested with this tick. Cattle and beaver are also reported as hosts. Fortunately humans rarely get attacked by this tick. The people that do are generally hunters who skin an infested moose after a hunt.

Did the late springs in 1996 and 1997 harm winter tick populations in northwest Minnesota? Last April 1996 when ticks were dropping off their hosts, the ground in many areas was still covered with snow. In late May and early June severe flooding occurred. Similar circumstances occurred in 1997. Perhaps these events will greatly limit the tick population for awhile. Only time will tell.

Selected Reference for more information on parasites of moose:
Anderson, R.C., and Lankester, M.W. "Infectious and Parasitic Diseases and Arthropod Pests of Moose in North America." Naturaliste can., 101: 23-50, 1974.

Artwork and most of the text were provided by Mr. Gary Averbeck
Department of Veterinary Pathobiology
University of Minnesota, St. Paul, Minnesota

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Last updated on: June 13, 2000
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