National Geographic

Here’s What Happens When A Tick Bites You

Castor bean tick, or sheep tick. Credit; Richard Bartz

Castor bean tick, or sheep tick. Credit: Richard Bartz

When a tick bites, it does more than just stick you with the pointy end. Here’s what happens, in far more detail than you ever cared to know. You can thank Dania Richter from the Charité University Hospital in Berlin, who carefully analysed the mouths of ticks, and filmed them as they fed on the ears of recently euthanized mice.

The mouthparts of the castor bean tick (Ixodes ricinus) consist of three main sections. The centrepiece is a long, sword-like structure called the hypostome. It has rows of backwards-curving spines along its edges, as well as its entire bottom face. It also has a groove running down its centre, which channels the tick’s saliva into its host, and channels the host’s blood into the tick.

On top of the hypostome is a pair of chelicerae—long rods that end in hooked teeth. The chelicerae are telescopic, so they can extend to just beyond the hypostome’s tip, or pull back to around half its length. They’re also mobile—their toothed tips can swing out to a 45 degree angle.

Here's what the chelicerae look like when fully extended. Scale bar = 30 micrometres

Here’s what the chelicerae look like when fully extended. Scale bar = 30 micrometres

When a tick wants to bite, it starts by gently coursing its chelicerae over the skin of its host (at about 0:25 in the video). Each one ends in a tooth that’s tapered to an especially sharp point, which scrapes and punctures the skin with very little force. This also releases smells and other chemical information that the tick can weigh up.

Now, it’s time to break in (1:35 in the video). The chelicerae start to flex their tips. At first, they take turns; eventually they move together. With each sweep, the teeth snag on the host’s flesh and bury the chelicerae even deeper into the skin. After 30 of these movements, the entire tips are firmly embedded.

The tick then contracts both of its chelicerae while flexing both tips, like it’s doing a nightmarish version of a breaststoke (2:20 in the video). The motion drives the rigid, sword-like hypostome into the skin, and the backwards-facing spines keep locked in place. The chelicerae relax and extend, before flexing and retracting again. Each stroke ratchets the hypostome deeper and deeper. After six of them, it’s completely buried and the tick starts to feed.

This is a very different sequence of events to what happens when a mosquito bites you (and you can watch a video of that too). That’s because ticks, unlike many other blood-suckers, are adapted for the long haul. A mosquito bites, sucks and quickly leaves. A tick bites… and stays there for days. It needs to attach itself very firmly so that it can’t be easily dislodged. It does so with the curved teeth and spines on its mouthparts, and by burying them very deeply.

The same sticking power is also vital for the parasites that ride inside ticks, like the spirochete bacteria that cause Lyme disease. They only spring into action when the tick starts feeding, and they need to time make their way from the creature’s guts into its bloodstream, into its salivary glands, and finally into its host. The whole process can take a couple of days. If the tick wasn’t so good at anchoring its face into a host, Lyme disease wouldn’t exist.

Reference: Richter, Matuschka, Spielman & Mahadevan. 2013. How ticks get under your skin: insertion mechanics of the feeding apparatus of Ixodes ricinus ticks. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2013.1758

There are 9 Comments. Add Yours.

  1. BioTay
    October 30, 2013

    I would like to see how the tick retract its own hypostome. All these spines look so rigid!

  2. JohnR
    October 30, 2013

    Boy, God has a wicked sense of humor!

  3. Dan J. Andrews
    October 30, 2013

    “Here’s what happens, in far more detail than you ever cared to know. ”

    That is pretty much what I thought when I read the title. In fact, having been fed on by a tick or few I almost didn’t read it because I really didn’t want to know. Curiosity won out though. Next time I find embedded in my skin I’ll take a bit of time to marvel at how it broke into my skin before I terminate it with extreme prejudice (incidentally, also reread the Lyme disease chapter in Spillover this past weekend).

  4. Zach Miller
    October 30, 2013

    See, this is one of those times where ignorance is bliss.

  5. pam spermia
    October 31, 2013

    out of all the organisms on the planet I hate nothing more than… THE TICK!!
    but ahh well, as human being we should be able to avoid them easily.

  6. Joanne Drayson
    October 31, 2013

    Willy Burgdorfer found that although the mechanisms of transmission to host were still under investigation Lyme disease could be transmitted by saliva of tick, which is the first thing injected into the host and by regurgitated of stomach contents or possibly by means of infected fecal material.
    Far too many assumptions are made about times to transmit Borrelia to humans.
    Not enough attention is taken of the burden of disease ticks can transmit, in Italy one tick was found to have 108 genera of bacteria – several of which are known to cause human health problems and that is before we consider virus, protozoa and other pathogens or their interaction within the human host.
    Whilst understanding this unique process helps to move science along there is so much yet still unknown about Borrelia in relation to human health so many statements made to patients based on uncertain science. The James Lind Alliance reviewed the research with Public Health England overseeing the process and identified top ten research priorities http://www.lymediseaseaction.org.uk/wp-content/uploads/2013/01/JLA-top-10.pdf

  7. Richard
    October 31, 2013

    This is helpful, the photos are excellent. Earlier this year, I interviewed Dr. Alan MacDonald, a famous pathologist and disease expert who offered much more detail on the incredible “anatomy of a tick assault.” See all three videos here: http://www.youtube.com/user/ADRSupport/videos

  8. samuel
    November 4, 2013

    *burns pile of ticks*

  9. Michael Fugate
    November 4, 2013

    ….which all reminds me of one of the best animated series of all time “The Tick”. http://www.imdb.com/title/tt0112196/
    Not nearly as scary as this, but great fun – no hypostomes employed on evildoers though.

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