Itch, magnified

My Advanced Ecology and Biodiversity class continues its investigation of our local tick populations. A few weeks ago, we collected ticks in the field and preserved some of them in alcohol. We’ve now looked through these collections using microscopes. We collected only “seed ticks,” little animals that are barely visible to the naked eye, so this close examination lets us identify the life stage and species of each individual.

For anyone who has been attacked by a swarm of seed ticks, the view down the microscope is at first a little horrifying. These agents of suffering loom up at us, unlocking a shiver of fear. Several of us unconsciously reached down to scratch our legs as we looked through the eyepieces.

After a few minutes and, paradoxically, at higher magnification, the little creatures take on a certain rotund charm. The fact that they are pickled helps a lot. We can tell larvae (the first life stage after the egg) from nymphs (the stage that comes after a larva feeds and molts) by counting legs: six for larvae and eight for nymphs. If only all biological identification were so easy.

The majority of the ticks in our collection were larvae. These two are lone star ticks, identified by the shape of the mouthparts and the number of crenelations on the rear of their body (this feature is hard to make out, especially in home-spun photos like these —  taken by holding a camera up to the microscope lens…):

We also found a few dog tick larvae. Note the different shape of the mouthparts:

Nymphs were much less abundant, although we did find a few. The following is a the nymph of a lone star tick (the hindmost pair of legs is tucked in, but you can see them if you look closely).

Undoubtedly, the mouthparts are the most fascinating part of the animal. The two outer parts are the palps, used to feel around for a choice spot to drill. The inner portion is made from two knives and a barbed feeding tube. The knives, called chelicerae, open the skin. Then the tube, the hypostome, is inserted and cemented. The cement both holds the animal in place and serves as a gasket to stop leaking. The animal then spits a mixture of chemicals into the host to loosen up the blood. The ticks are fracking us for protein. Without the permission of the landowner.

Of course, when ticks feed, they may also transmit diseases such as Lyme, Rocky Mountain Spotted Fever, and Ehrlichiosis. In the case of Rocky Mountain Spotted Fever, the larvae may hatch already carrying the disease, having received it through the egg from their mother. But the other diseases are not transmitted through eggs. Instead, larvae become infected when they feed on mice and other vertebrate hosts. Larvae only feed once before turning into nymphs. So a bite from a larval tick is generally less dangerous to a human than a bite from a nymph or adult. The latter have fed on other vertebrates and are more likely to carry disease. Good to know, but little comfort when your legs are aflame with the itches of a hundred bites.

My students are currently extracting DNA from the animals to confirm our identifications and to test for diseases. I’ll keep you posted. In the meantime, remember to tick check. These diseases are a reminder that parasitism and disease are ubiquitous components of the ecology of our world.

Scratch, scratch.

14 thoughts on “Itch, magnified

  1. Joe Willis

    David: Thanks for sharing your site. How did you find mine? I enjoy natural history exploration and writing a great deal, but I am still an amateur when it comes to making the best use of the web for spreading my creative endeavors. I’m working on a book that is a cross between a daily nature journal and a collection of natural history essays, all supplemented by photography and original art. Hoping to be ready by early spring. I’ll definitely check into your book. My college education was mostly in the South – Tulane, U Fla., and Gulf Coast Research Lab. Are you a native Tennesseean? Thanks again for sharing your site. Joe Willis, blackoaknaturalist

    ________________________________

    Reply
    1. David George Haskell Post author

      Hi Joe,

      Your book sounds very interesting. You live in a great part of the country for natural history.

      I’m a born-again Tennesseean. In other words, not a native. I’ve been here 16+ years now. It is a fabulous place for forests and animal diversity.

      I’d say that we’re all amateurs in figuring out the best way to use the web/other media to communicate. Technology definitely keeps me on the steep (and fun) part of the learning curve.

      Reply
  2. Denise Dahn

    I’ve only had one tick in my life, despite living long enough that I’d rather not say, and spending a good deal of that time in woods. One good thing about the Pacific Northwest….lots of rain, but not too many ticks….I like the fracking reference, though. Now, when I think of those oil/gas companies, I think I’ll picture ticks. Good analogy!

    Reply
  3. Anonymous

    As I read your report an itch began to appear on my left arm then on my right. I stopped reading until they disappeared. Then I finished the gripping post.

    Reply
    1. David George Haskell Post author

      Good point. I discuss exactly this point in the book. The world is FULL of examples of parasites that cause massive amounts of pain.

      You seem to be arguing with someone other than me here. I’m no intelligent design advocate or creationist.

      Reply
    2. David George Haskell Post author

      Well, yes. Darwin made this point very well. As I discuss in my book. That is the whole point of the last 150 years — old notions of theology need massive updating or elimination in light of scientific discoveries.

      Reply
  4. Ann Fraser

    Ah, yes. I ran into a patch of those seed ticks my first year in Sewanee and didn’t realize until many had had a good feed on my ankle. The itch was unbearable, but like with chiggers I have found that hot water (as hot as you can stand) run over the afflicted area (or a cloth dipped in boiling water and then held to the skin) deadens the itch for 4-6 hours, long enough to fall back asleep and get a good night’s rest.

    Reply

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