Pacific Black-legged Tick (Ixodes pacificus)
DON’T BRING A TICK HOME FOR DINNER!
May 20, 2009
Which creature do you consider to have the highest revulsion factor rating?
When I wrote the recent article on Rats!, I’m sure some of you were squirming in your seats, shivering with memories of battles lost and won to rid your homes of rats. But rats do have their place in this world, as food for other predators, as recyclers of garbage, as scientific tools in the search for cures to human ailments.
I have been trying to think of a reason that ticks exist, how they might fit into our limited understanding of ecological interconnections. I suppose if you remove our human perspective of good and bad (for us), they have a place as a reservoir for bacteria, and maybe this plays a role in keeping populations in balance. There is a small parasitic wasp which lays its eggs in ticks and apparently guinea fowl consume them. Personally I find them really tough to appreciate, particularly when I find them latched onto some part of my anatomy.
Vancouver Island is home to about eight tick species but in Metchosin, the most common tick that you will find is the Western Black-legged tick (Ixodes pacificus). It is also the only one that will attach to humans. A walk through almost any natural landscape on a pleasant day from November through June will end with a few ticks trying to find a meal on my small dog, Maggie. Sometimes I’ll see them crawling over her white fur, looking for the safest location to settle and start feeding. Other times I will find them by accident as I give her a rub and feel a grey lump protruding, sometimes behind her ears or often on her forehead.
For two years I collected all the ticks I pulled off her, dropped them into a container of alcohol and eventually brought them to the Royal BC Museum, entomology (insect) section. They displayed a variety of colours, ranging from black to brown, grey, red and white and I thought I had at least several types of ticks in my little jar. Expert analysis pronounced all the ticks as Western Black-legged ticks in various stages of development.
These ticks have a four stage life cycle. Adults lay eggs that are deposited on leaves or in the leaf litter. The eggs hatch and the immature, minuscule ticks (larvae) immediately look for an appropriate host, usually small mammals. They attach to their host, feed on blood and detach. In their next stage, as nymphs, they again attach to a host - they prefer alligator lizards with deer mice a close second - feed, detach and molt. The top photo shows a northern alligator lizard on Camas Hill, Metchosin, with a tick attached, midway between the eye and front leg. As an adult tick, they prefer large mammals such as deer, cattle or humans, probably because they offer a large blood source to ensure their eggs a good start. They find their new hosts by climbing onto some low growing plants or grass. From here they exhibit behaviour known as questing, where they wave their legs in the air, sensing a prospective “mobile home” through organs which detect carbon dioxide and heat. In one survey adult ticks were found more often on south-facing hillsides, questing from salal, Scouler’s willow and wild rose; the same habitat where you’ll find alligator lizards. Adult ticks consume 200 to 600 times their unfed weight in blood.
The female tick can produce 1000 to 8000 eggs, after which she dies; the male dies after reproduction. Ticks in the larval stage are minute, the size of a poppy seed, while an engorged adult can expand to the size of a bean or grape. Studies have shown them to be more prevalent just after rain, with female adults reaching their peak populations in May.
Western Black-legged ticks can be carriers of Lyme disease, a potentially serious disease that can affect joints, the heart and the nervous system. There is some controversy as to the incidence of Lyme disease in ticks in this area with some studies showing a low (less than 1%) incidence while others claim up to 30% rate of infection.
In some US states, including California, they have (rarely) been known to pass on granulocytic ehrlichiosis rickettsia to horses, which can cause fever, loss of appetite, loss of coordination and various other symptoms.
Ticks inject an anesthetic that can prevent you from feeling them while they are feeding. If you are unlucky (like me!) and find a ramble in the hills has resulted in an unwanted hitchhiker, carefully remove the tick with tweezers placed firmly at the head, pulling gently and slowly but not twisting, allowing the tick to disengage its mouthparts. Try not to squish the ticks abdomen as this can expel contents from the tick’s stomach into the wound and thereby transfer disease bacteria. You can save a live tick in a jar with a dampened cotton ball, if you intend to send it for testing, but I just flush any I find down the toilet. Wash the bite area with soap and water and then swab with hydrogen peroxide or alcohol. I seem to break out in a swollen ulcer-like, tender wound which can be slow to heal but this doesn’t occur with everyone and does not mean that you have contracted Lyme disease, it is probably a reaction to the saliva. If you develop a fever or flu-like symptoms within two weeks to a month of the bite or a red bulls-eye rash, you might have contracted Lyme disease and you should see your doctor. There is a vaccine for dogs but we humans don’t have that safeguard yet. Two weeks on antibiotics is the recommended course of action. The Centre for Disease Control has an excellent brochure on Lyme Disease and ticks that can be downloaded, see the reference at the end of the article for the website.
There are other less common diseases that ticks can carry, so it is best to protect yourself from a bite in the first place. Don’t let the fear of ticks prevent you from exploring the countryside, hiking up hillsides and into the woods. Wear long pants tucked into socks, a long-sleeved shirt and a spray of an insect repellant such as Deet to reduce your chance of harbouring these creatures. And enjoy your hike!
BC Centre for disease Control: http://www.bccdc.org/topic.php?item=83
Arnason, Carl, S. 1988. Biology of the Western Black-legged Tick, Ixodes Pacificus