In a Pinch — the Scorpion’s Chelicerae

12 Nov
The chelicerae of a scorpion are visible as it devours a cricket.

The chelicerae of a scorpion are visible as it devours a cricket.

8legs2many today!  I found this little guy hunting near a lightsheet at the Welder Wildlife Refuge.   As a general rule of thumb smaller pincers mean a more powerful sting, so I took care handling this little guy.  Above, you can see him chowing down on a feeder cricket I gave him.

Like spiders, scorpions are arachnids, with eight pairs of walking legs.  Their large front claws are not true legs, but actually modified pedipalps, appendages on the prosoma used by chelicerate arthropods for handling food.  While snapping pictures and shooting video clips of this guy I also got a chance to get a close up look at another cool appendage– the chelicerae.  These are two sharp pincer-like mouthparts used to grab the food and tear off small pieces.  These are pulled into the preoral cavity, where food is digested externally prior to being sucked down in liquid form.  Chelicerae are unique to a subgroup of arthropods called the Chelicerata–which includes arachnids, horseshoe crabs, and a weird little group called the sea spiders.  In spiders the chelicerae bear the fangs (these were the metallic green mouthparts we saw on the bold jumping spider a few posts ago).

Scorpions actually make pretty interesting pets, needing only a warm dark environment with some kind of refuge.  Scorpions (and other arachnids) lack the cuticular layer of wax which protects insects from dessication. * It is important to maintain high humidity to prevent them from drying out, particularly for tropical species.  They are nocturnal, and so most active at night, which is the best time to feed them.  Because they are adapted to living in darkness, they are sensitive to UV light, which can harm them with prolonged exposure.  They also fluoresce vividly under a blacklight, which can be a fun way to hunt for them at night, although, again, longterm exposure should be avoided.

*Edit:  See comments below.  Thanks, Dave!


6 Responses to “In a Pinch — the Scorpion’s Chelicerae”

  1. TGIQ November 14, 2010 at 10:13 am #

    I am wrong in thinking that cricket looks to be the same size as (or bigger than!) that scorpion? Crazy!

    • 6legs2many November 14, 2010 at 10:32 am #

      It is a fairly big cricket, but apparently no match for the scorpion’s stinger!

      I’m always impressed by how big of prey spiders and scorpions will tackle. My little jumping spider will not only take down a cricket twice his size, but then drag it backwards up the side of the container to eat in safety.

  2. Dave November 14, 2010 at 12:01 pm #

    I wonder if your scorp is Centruroides vittatus the Striped Bark Scorpion. Ted MacRae at Beetles in the Bush posted some pictures on 5 November that seem to have the same colour pattern. The sting is supposed to be very painful.

    I’m not sure you are correct about scorpions lacking an epicuticular wax layer. I thought they had one and that some have among the lowest rates of water loss reported in desert animals. If you were ever so cruel as to drop a scorpion in a vial of alcohol, you might notice how long it takes them to die. Something interesting is going on with their cuticle.

    Lots of spiders sit around in the sun all day and most mites have such a large surface to volume ratio that without waterproofing they would be in trouble even at relatively high humidities. I think arachnids in general have good water-proofing.

    • 6legs2many November 14, 2010 at 2:30 pm #

      The pictures at Beetles in the Bush do look about right. I run into these guys fairly commonly doing field work around here, although mostly at night.

      You seem to be correct about the wax layer. I’m not sure where I picked up that bit of misinformation. I believe that may have been the explanation given me for why spiders need to be preserved in alcohol rather than pinned. Lies!

      I’ve cared for tropical scorpions in the past that need very high humidities. Apparently even desert scorpions have high humidities in their burrows–important for molting if nothing else.

      I’m glad to know about the broader presence of the wax layer among terrestrial arthropods. It’s a fairly logical adaptation. Various Googled sources seem to indicate that myriapods lack it, however. I think? You can tell my education has been insect-biased.

  3. Dave November 15, 2010 at 9:54 am #

    I used to know which arthropods did and didn’t have wax layers, but I haven’t had to teach it in over a decade (and besides, new research may have shown that what I taught was wrong). However, I think you are right about centipedes at least. Also I think isopods have a hard time.

    Also, you are right about moulting (and also egg hatch – although I guess scorpions don’t have external eggs) – that is where even well protected arachnids have a hard time. For example, if you want to eliminate stored product or dust mites, if you can keep the relatively humidity in their microclimates below ~70% (50% is a good target), then you will soon have only adults and soon enough none. Beats using a chemical, especially if they are infesting your insect colony.

    Most spider ‘abdomens’ are soft and will shrivel when dried. So if you do want to pin them, you’d need to vacuum dry or maybe HMDS the smaller ones. I have the same problem with most sawflies – they look really sad on pins.

  4. Ted C. MacRae November 21, 2010 at 10:50 pm #

    Most awesome view of cheliceral chomping!

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