The other sea spiders

Put yourself in my place: You’re collecting mantis shrimp by cracking reef rubble on the beach of an island on the Great Barrier Reef (I know, there are worse ways to spend your day). You split one particular rock, and instead of shrimp, out pours a brood of arachnids. Not pycnogonids, not spider crabs… freaking spiders! Well, at this point, if you’re me, you shriek like a little girl and frantically crab-walk backwards while brushing yourself off.

In that embarrassing moment I had learned something new: There are arachnids that live, partially, in the ocean. These small Desid spiders live in intertidal rubble. During the day they hide in silk-sealed air chambers within the rubble. At low tide they come out to hunt stranded critters along the tide pools.

A marine spider, Desis martensi, on an out-of-water coral head. It has captured what looks like a pistol shrimp. Photo: Wild Singapore

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11 Responses to “The other sea spiders”


  1. 1 Laurence March 17, 2010 at 9:37 am

    I think I’d be shocked too. It’s definitely not something you’d expect to find on a beach!

  2. 2 kevin z March 18, 2010 at 12:59 pm

    Wow! Even I haven’t heard of this before. Way cool!

  3. 3 Mike Bok March 18, 2010 at 1:04 pm

    Unfortunately, I can find almost nothing about them online or in the literature. I wanted to make a more elaborate post, but I couldn’t find any good info.

  4. 4 Danielle March 22, 2010 at 12:11 am

    That is so cool! I didn’t know there were any marine spiders either. Fresh water ones, yes but not anything like this.

  5. 5 John Sloan March 22, 2010 at 10:21 pm

    Here’s a paper that describes the sister species, D. robsoni (now placed in D. marina) – includes some diagnostic diagrams, and info on the biology. There’s a bit in there about D. martensi as well:

    http://rsnz.natlib.govt.nz/volume/rs…_00_002330.pdf

    I enjoy your blog!

  6. 6 John Sloan March 22, 2010 at 10:25 pm

    Here’s the link again (I don’t think it came out right the first time):

    http://rsnz.natlib.govt.nz/volume/rsnz_11/rsnz_11_00_002330.pdf

  7. 7 Mike Bok March 22, 2010 at 11:50 pm

    Nice find, John!

    It sounds like Dr. Martens account is similar to how I learned about these arachnids:

    I tore off pieces of coral and broke them up to get at the creatures hidden within. To my astonishment I several times observed spiders hurriedly escaping…

    He apparently chose to leave out the part where he yelped and frantically scrambled away.

    I’m glad you like my blog. Thanks again for finding that paper.

  8. 8 JP Lim April 5, 2010 at 1:43 am

    I’ve seen spiders like these on an island in the Philippines, crawling on a reef during low tides. However, I’ve asked around (I’m a zoologist) and no one seems to know about them. I’m now wondering if they’ve ever been described from my country yet.

  9. 9 Mike Bok April 5, 2010 at 11:43 am

    It is possible. I can’t believe how little info is out there about these unique and apparently abundant spiders.

  10. 10 Ria Tan November 22, 2013 at 10:14 pm

    How nice to see that my photo of this amazing spider is useful to your wonderful blog! Yes, this spider is quite abundant, and one of the best ways to spot one is too look at your trouser leg when out on the reefs at low tide; there is often one exploring it. But it will soon hop off if it discovers nothing edible there.

    I’m sorry this reply is so late after your post, but there is more information about this spider on the Singapore National Parks Board website http://www.nparks.gov.sg/cms/docs/redbook/2aDesis%20martensi.pdf

    As it states in the pdf, the spider was described from Singapore. The document also has more information about the spider’s behaviour, which I’ve consolidated in my fact sheet which includes lots more photos of this awesome little predator in Singapore. http://www.wildsingapore.com/wildfacts/arachnida/desis.htm

    Thank you once again for featuring the spider on your blog.


  1. 1 Arthropods in pop culture: Attack of the Camel Spiders « Arthropoda Trackback on June 30, 2010 at 3:05 pm

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I have moved.
Arthropoda can now be found here.

Michael Bok is a graduate student studying the visual system of mantis shrimp.

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