Dermacentor albipictus, the winter tick, is a species of hard tick that is an external parasite of moose (Alces alces) in North America. As early as 1909, Ernest Thompson Seton described the winter tick as a greater enemy of the moose than were "wolves, bears, and cougars."
The tick can be found all across North America, and has a large geographic distribution. While it can be found in several different habitats, it is often located in areas with a presence of moose.
There is evidence that increasing populations of the winter tick may be responsible for a steep decline in the Eastern moose population throughout the southern half of their range. In recent years, heavy infestations of up to 75,000 ticks have been seen on single moose, and can lead to the death of the animal.
The winter tick is sexually dimorphic, with adult females larger than the males. The adult female is mostly reddish-brown, but with a white dorsal shield behind the head. The smaller adult male is dark brown with some white markings.
Female ticks become unusually large toward the end of winter, measuring up to 15 millimetres (0.59 in).
The life cycle of Dermacentor albipictus lasts for about a year, and it is a single-host tick. This means that the entire life cycle of the tick (larvae, nymphs, and adults) progress on a single host animal. First, in late summer larvae hatch from eggs. After lying dormant for some time, they start to ascend vegetation and to group in clusters on plants up to 1.25 m in height. This allows them to latch onto animals that pass by and begin to feed on their host. While on this host, the larvae go through the stages of nymph and then finally transform into an adult.
Addison and McLaughlin, in a 1988 study of ticks on young moose in captivity, reported that larvae became nymphs about 10 days after being applied to the moose. Nymphs then underwent a long diapause before becoming adults in roughly mid-February. One moose, which had been infected with larvae 37 days after the others, still showed a similar timing of adult ticks appearing. The authors suggest the diapause may serve to delay maturity until the onset of warmer weather, as has been seen in other species of ticks.
During late winter, the ticks mate, and blood-filled females drop off the host to lay their eggs and die. For captive moose observed in Ontario in 1988, tick detachment occurred in late March or early April.
Effect on ecosystems
Tick populations and their effects on moose have been observed to vary from year to year. Winters that are shorter and warmer have been shown to correlate with increased numbers of ticks in moose populations.
The tick not only affects moose, but also other wildlife that can be connected with the moose. In 2001 the moose abundance on Isle Royale was around 1200, but due to the tick the moose abundance fell to around 400 in 2007. With the decreased moose population, the main food source of the moose--various shrubs species and balsam fir--has seen an increase in abundance. .
- Addison, Edward M (January 1, 2007). "White as a Ghost, Winter Ticks and Moose". Journal of Wildlife Diseases. 43 (1). doi:10.7589/0090-3558-43.1.150. Retrieved March 8, 2019.
Our understanding of winter ticks (Dermacentor albipictus) and moose (Alces alces) is largely a 20th century story beginning when Seton (1909) described winter ticks as a greater "enemy" of moose than were wolves, bears, and cougars. Until 1980, field observations comprised the literature on winter ticks and moose. In the last two decades of the century, Bill Samuel, along with colleagues in Alberta and others, examined the relationship between winter ticks and moose using thorough experimental and field studies.
- "Tick Species of Maine - Winter Tick or Moose Tick".
- Hari Sreenivasan (2014-04-07). "What's devastating the wild moose population in New England?". PBS Newshour. Retrieved 2014-04-08.
- Dell'Amore, Christine (2015-06-01). "What's a Ghost Moose? How Ticks Are Killing an Iconic Animal". National Geographic News. Retrieved 2019-03-08.
The reason is likely climate change, biologists say, which is ushering in shorter, warmer winters that are boosting the fortunes of winter ticks. The tiny creatures latch on to moose here in staggering numbers: One moose can house 75,000 ticks, which are helping to drive a troubling rise in moose deaths, especially among calves.
- Samuel, Bill (2004). White as a Ghost: Winter Ticks & Moose. Federation of Alberta Naturalists. ISBN 978-0969613466.
- "Moose winter tick".
- Addison, Edward M; McLaughlin, Robert F (1988). "Growth and Development of Winter Tick, Dermacentor albipictus, on Moose, Alces alces". The Journal of Parasitology. 74 (4): 670–678. doi:10.2307/3282188. Retrieved March 14, 2019.
Engorged females first started to detach by 24 March, and many had engorged and detached by early April (190-192 days after infestation).
- Ritcey, RW; Edwards, RY (1958). "Parasites and Diseases of the Wells Gray Moose Herd". Journal of Mammalogy. 39 (1): 139–145. Retrieved March 14, 2019.
There is annual variation in the abundance of ticks on these moose…In years of heavy loads some extreme conditions have been recorded. Through late March and early April in 1952 most moose beds were bloodstained and contained ticks. Thirty-one ticks were found in one bed. In that year a weak calf, reported by Patrolman C. E. Gaglardi, was captured and examined. It had ticks over most of the body with the exception of the back and shoulders…There was little space for more ticks on the ears, inside or out. The body was dotted with clusters averaging three or four ticks each.
- Samuel, WM (2007). "FACTORS AFFECTING EPIZOOTICS OF WINTER TICKS AND MORTALITY OF MOOSE" (PDF). Alces. Retrieved March 8, 2019.
Die-offs of moose (Alces alces) associated with, or attributed to, winter ticks (Dermacentor albipictus) are widespread and have been reported since the early part of the last century...The proposal that warmer and shorter winters result in increased survival of adult female ticks dropping off moose in March and April, and increased tick populations on moose the following winter, was generally confirmed. Annual changes in hair damage and loss on moose, which are documented from the air, coincided with annual changes in numbers of ticks on moose, providing managers with a survey tool to monitor and estimate changing numbers of ticks.
- "Small Creature, Big Influence".