Ticks seem to be everywhere this season, in the woods where
I walk, on my dogs and cats, crawling up my pant legs, and this past spring,
all over Facebook-everyone was posting about the spring emergence of the ticks.
And I get it, Lyme (not to mention all the other tick borne diseases) is
sometimes difficult to treat and can be life altering for some of sufferers.
But this isn’t a program about health or disease, it’s about the natural world,
and for better or worse, ticks are part of that world.
Ticks are arthropods, a group of animals that is
characterized by having a chitinous exoskeleton and jointed legs. Insects and
crustaceans are classes of arthropods we are all familiar with. Ticks are in
the class Arachnida with spiders and mites, a sub group of arthropds that
typically have 8 legs and specialized mouth appendages. In reading up on ticks
I learned some things that are fascinating, and so even though they are one of
the most hated groups of animals around, I want to share what I found out.
Ticks, like many insects, undergo incomplete metamorphism,
which means that they hatch from an egg into a form that is similar to the
adult, usually just smaller and sometimes with less well developed appendages
or body parts. For example the deer ticks we worry about so much here in Maine
have only 6 legs in this newly hatched stage. Typically this stage is called
larval, though you shouldn’t confuse it with the larval stage of an insect like
a butterfly that undergoes complete metamorphism. In those organisms “larva”
means caterpillar or grub or maggot, something that looks nothing like the
adult. Baby or larval ticks look like tiny ticks, and they feed on the same
thing as adults; blood. Tiny larval ticks require a blood meal before they can
grow into the next stage of life, once they have eaten, they molt their
exoskeleton and emerge as a nymph. Nymph ticks often look just like adults,
only smaller. They also need a blood meal in order to molt and grow into the
last stage of life, the adult. The job of the adult tick is to mate, and only
the female needs a blood meal, so that she can lay her eggs, and the cycle
starts over. So, egg hatches, larvae, feeding, nymph, feeding, adult, feeding;
they eat three times (and only three times) during their lives which can last
over a year here in Maine.
Three times in a year and a half, that isn’t much food, for
that much time. Each time they bite they have to get enough food for months.
How they do it is really interesting. We all know that ticks embed themselves
into the skin of their victim, staying attached for days while they suck out
the blood they need to further their life cycle. Ticks have specialized mouth
parts that work in tandem, one part ratchets while the other part drives deeper
into the skin. These parts are lined with reversed direction barbs, so they
can’t simply slide back out. Once the mouth parts are fully embedded, no energy
is required for the tick to stay there and feed.
Ticks are very small animals, yet they need to get enough
food to sustain them for months from just one feeding. If you have ever seen an
engorged tick on your dog or cat, all shiny and gray and swollen, you know that
ticks have an abdomen that can stretch to hold a large volume of blood. Even
more remarkable though is the level of sophistication the ticks have when
feeding. As the ingest blood from their host, it is immediately digested and
separated out. Ticks keep the red blood cells, apparently the most nutritious
fraction of blood. All the rest, the plasma fluid, salts, other blood cells,
gets excreted back into the host’s body. So the ticks suck your blood, take
only the best parts, and spit the rest back out, thus concentrating their meal.
That is how they are able to feed once and live for many months on that one
meal. And that is why, for animals that have a high tick burden, anemia can
become a real problem.
Detested, persecuted, hated; ticks get a bad rap in the animal
world. They are only doing what we all are though, living the only life they
know how to lead, fulfilling their biological destiny along the way.
References:
About ticks and climate change http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2582486/
Tree of Life site for Arachnids http://tolweb.org/Arachnida
Comprehensive list of ticks in Maine from Maine Medical
Center Research Institute: http://www.mmcri.org/home/webSubContent.php?list=webcontentlive&id=108&catID=4&subCatID=19
A Maine based company with lots of info on their website: http://www.mainelyticks.com/familysafety-lifecycle.html
Tick mouthparts: http://www.nytimes.com/2013/10/30/science/earth/how-does-a-tick-do-its-dirty-work-research-video-offers-a-clue.html?_r=0
Thank you Ed Yong for citing this article (though no one
seems to have looked at how they detatch themselves and get those amazing
barbed mouthparts out of your skin): http://rspb.royalsocietypublishing.org/content/280/1773/20131758
Moose, ticks and anemia http://www.nwf.org/Wildlife/Threats-to-Wildlife/Global-Warming/Effects-on-Wildlife-and-Habitat/Moose.aspx
