Ticks: The Basics

 

Host feeding patterns vary significantly between tick species, as they can be one-, two-, three- or multi-host ticks.

  • One-host ticks spend their lives almost entirely on the same host. The moose tick, Dermacentor albipictus, is an example of a one-host tick.

  • Two-host ticks feed as larvae and nymphs on the same host, then fall off, molt into adults and find a new host as adults. There are no two-host ticks in Canada.

  • Three-hosts ticks feed on a different host during each life stage and leave the host to molt. Most hard tick species in Canada are three host ticks, including Ixodes scapularis (blacklegged tick).

  • Multi-host ticks feed on multiple hosts throughout their lives. Soft ticks are generally multi-host ticks, since they feed multiple times even within one life stage.

 

In order to find a host, ticks use a variety of mechanisms. They can sense rapid changes in temperature or light, vibrations, host odours or carbon dioxide. Hard ticks undergo a process called questing, in which they climb up on vegetation and wait with their first set of legs out for a host to pass by. Soft ticks generally crawl to their hosts.  It is important to note that ticks do not fly or jump to get to their hosts.

 

Aside from these common features, each tick species can differ significantly in regard to anatomy, the host species on which it feeds on, the habitat and climatic conditions suitable for survival, the seasonal activity patterns (referred to as phenology) and the pathogens which it can transmit (some transmit none).

When we say ‘tick’, we are actually referring to over 900 distinct species. The majority of these species are found in tropical and subtropical areas, but a subset are well-adapted to temperate areas (and a few even to tundra!).

 

Taxonomically, ticks are within the class Arachnida (subclass Acari) and Order Ixodidae. They are further divided into three families. Two of these families, Ixodidae (hard ticks) and Argasidae (soft ticks), are found in Canada.   

Hard ticks are characterized by a hard shield on their dorsum (back). Generally, hard ticks are active during the daytime and feed slowly over a span of days. In contrast, soft ticks lack the hard dorsal shield and feed at night rapidly over minutes to hours. In Canada, there are 40 recognized species of ticks, of which 32 are hard ticks. The eight species of soft ticks are found only in Alberta and British Columbia.

 

Ticks have three active life stages (or in stars): larvae, nymphs and adult male or female. Larvae have only 6 legs, while nymphs and adults have 8 legs. Adults range in size from 1 to 5 mm unfed to up to 20 mm fed.

           

Ticks are obligate feeders – meaning they need to take a blood meal from a host in order to survive, undergo development and eventually reproduce. Hard ticks will take one blood meal per life stage and then molt to the next life stage, while some soft ticks may take multiple blood meals.

Reference: Lindquist, E. E. et al. A Handbook to the Ticks (Ixodida: Ixodidae, Argasidae) of Canada. (Biological Survey of Canada, 2016).

PETS AND TICKS!

In 2016, Dr. Scott Weese of the Ontario Veterinary College launched the Pet Tick Tracker to help monitor changes in tick populations. Through this online tool, pet owners could submit reports of tick findings - and the response was overwhelming! He's now teamed up with Drs. Katie Clow and Michelle Evason to create Pets and Ticks - a comprehensive website that brings the Pet Tick Tracker together with up-to-date, evidence-based information on ticks in Canada.  

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