Wednesday, August 10, 2016

Mini Pirate

A tiny spider walked down my wall. I was busy and barely noticed until it was right in front of me, when I saw that it was oddly proportioned; the head end* was larger than the belly**. (*Cephalothorax and **abdomen.)

The camera saw it better than I did. The belly was an odd shape, as well as being too short.

A Pirate spider, probably Ero canionis.

I had never seen one like this before. I sent the photos in to BugGuide, and they, as they do so well, identified it overnight as one of the Mimetidae, the imitators.

Long, spiky legs, short, flared "skirt".

The pirates are spider killers. They invade other spiders' webs, and vibrate the threads as if they were insects caught in the web. When the owner investigates, the pirate leaps and bites her in the leg.

Spiders extend their legs using hydraulics, rather than muscles, as we do. To run, they increase the pressure in the cephalothorax (the head/upper body section), sending blood down the legs. Small muscles then return the liquid to the body, returning the legs to the relaxed position. So a shot of paralyzing poison to the legs soon invades the whole body. (Fang)
Mimetids are equipped with a spider-specific venom that paralyzes their prey almost instantly. (SpiderBytes. Interesting story on this page.)  

Evidently, a bite to the abdomen takes much longer to act. But the spider "knows" this, and heads for the legs.

My tiny pirate ran down behind a cabinet and was lost, but I'll be watching out for her. I'd like to see her in action.


  1. Wonderful photos and explanations. Thank you. I read this soon after I woke up, and it made me feel very awake even before I drank coffee. :-)

  2. As someone with an affection for spiders, I'm conflicted on who to cheer for in the inevitable feeding session.

  3. Did anyone noticed the sunglasses on its rear?

    1. Yes. especially in the second photo. Cool spidey!


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