Sunday, January 8, 2012

What’s Afoot in the AB Winter: 8-legged Moose Nightmare

Male Winter Tick

As a general rule, I don’t like ticks. Actually, that is an understatement: I loathe ticks! But it is winter and, even during this unusually mild version, there are few arthropods around to enliven the out-of-doors. Here’s an exception that showed up with the New Year, a bit earlier than expected, but a real live winter arthropod and not unattractive at that. My appreciation of this rather large (6.6. mm long) blood-sucking 8-legged fiend is influenced by the knowledge that it probably wouldn’t bite me: it is a male Winter Tick, Dermacentor albipictus (Packard, 1869).
Winter Tick-infested Moose - 3:12 AM
trail camera shot
 Winter Ticks appear to prefer to suck the blood of moose and their relatives (Cervidae – moose, elk, deer, caribou). Moose can be very heavily infested - the average load in late winter is 30,000 ticks (see Samuel* 2004 p. 31). Heavily infested moose spend more time rubbing up against trees and the like trying to remove the itchy ticks than feeding. The result is a Ghost Moose – skinny, with ragged coats, open sores, and a grey-white colour. Many such moose will die overwinter, but if they can last until May, most of the ticks will have dropped off and they have a chance to recover.
Ghost Moose at Dawn
 Winter Ticks are the only ticks you are likely to find in Alberta in the winter, so identification is not too challenging. The adults are ornate ticks, i.e. the dorsal plate (covering the whole body in the male, but only the part just behind the ‘head’ in females) is patterned and they have 11 posterior festoons (the tooth-like grin at the rear). A pair of small eyes on the margins of the plate and a spiracular plate with large ‘goblet cells’ (unless you know what small goblet cells look like, this isn’t a great character) completes the identification. Males also have a distinctively formed spur on the base of the first pair of legs. Adult males are not above wandering around looking for females, so you or your dog may pick-up one of these ticks while on a winter hike on a mild day. Usually, they would keep wandering until they found a moose with female ticks, but if they are more hungry than horny, the males may bite (or at least I was brought a Winter Tick male that someone claimed bit them near their eye).
Winter Ticks have eyes too (arrow)
 Most hard ticks (Ixodidae - the family that includes the Winter Tick) have three different hosts during their life cycle – one of the reasons they are so likely to pick-up and transmit a disease causing pathogen. Each life stage - larva, nymph, and adult – attaches to and feeds on the blood of a host until full and then drops off. Winter Ticks, however, usually spend most of their lives on the same host. The best place to learn about the fascinating story of the Winter Tick is Bill Samuel’s book (see below*), and SRD kindly provides a good factsheet, but I’ll give a quick overview of the highlights.
Mouthparts (upper) and coxal spur (lower)
 From late winter until early spring, you can find female Winter Ticks as blood-filled blobs (to ~1.5 cm diameter) attached to moose and other members of the Cervidae (deer, elk, moose, caribou), and rarely on other large herbivores (bison, cattle, horses) or smaller mammals (coyotes). Males feed a bit, but do not bloat, and wander the moose looking for females to mate. Once the females have dropped off to lay their eggs (about 5000 each), you might come across them on the ground or in the litter around moose wallows and the like. Some of these female ticks may have been buried in the litter by magpies – which will also eat the ticks directly off the moose. 
Magpies - boreal tick birds
Tick eggs lie dormant until late summer to early fall when they hatch into tiny (<1mm) seed ticks (larvae – with only 3 pairs of legs). Seed ticks hunt moose, usually by hanging on to low vegetation and grabbing a moose when it walks by. Sometimes larvae get on people by mistake, as we, much to our horror, found out one September, but they don't attach. The larva wanders the moose until it finds a good site to bite through the skin, suck blood, and then shed its skin to become a nymph. Nymphs hang out and wait for things to get cold before sucking enough blood to moult into adults.
Moose Fly - the business end
 You’d think that Winter Tick would be all the parasite nastiness that any animal should have to endure, but Mother Nature has a summer surprise for moose too - Haematobosca alcis (Snow, 1891), the Moose Fly. Just as the moose is beginning to recover its condition in early summer, these housefly-sized pests start to appear. The flies hang out on the back legs of moose, pierce the skin with their long proboscis, and cause large, open sores from which they feed.
Sores from Moose Fly bites
 If you notice a cloud of flies around the rear of a moose in summer, especially if there are sores on the hind legs, you are likely seeing Moose Flies. The flies lay their eggs in moose dropping, the larval food, so moose give these pests pretty much everything they need. The sores don't heal until frost kills off the adult flies but tend not to fester either. So, it seems likely that the flies introduce a substance that protects the sores from bacteria. You can read all the gory details at  another SRD factsheet and see better pictures of the sores than we have here. Next time I’m feeling persecuted by the mozzies, I think I’ll reflect on the life of the moose, and not complain so much.

*Bill Samuel. 2004. "White as a Ghost: Winter Ticks & Moose" Federation of Alberta Naturalists.

Alberta Sustainable Resource Development. 2004. Winter Tick - Fact Sheet #21.

Alberta Sustainable Resource Development. 2010. Moose Flies - Fact Sheet #30. 


  1. "Next time I’m feeling persecuted by the mozzies..."
    Definitely! (Although at our mid-continental position we have at most only smallish mosquitoes and persistent but mostly ineffectual deer flies to deal with.)

    I never knew there were ticks with eyes!

  2. Fortunately, deer flies are rare here and the horse flies (several species of Hybomitra) a bit too cumbersome to get in more than the occasional bite. I suppose they concentrate on the moose and other large ungulates too.