close encounters with Dolomedes spiders

recently molted Dolomedes spider with exuviae in background (Aug. 12, 2004)
(click on image for larger view)

Winter is begin to wear on me a little, and despite recent adventures such as the Mudpuppy Night, I’m beginning to long for my daily invertebrate safaris here at the farm. To remind myself of all the fun I’m missing, I decided to dig up some of photos and write about a few close encounters with Dolomedes spiders – the genus commonly referred to as the fishing spiders.

My earliest recollection of a fishing spider encounter occurred at my family’s cottage when I was about 6 or 7 years old. I was just drifting off to sleep on one of those rickety, old hide-a-beds in the living room, when something plopped itself down onto my eyelid. I lay very still for a few moments, my uncovered eye staring up into the darkness, as I tried to fathom what this thing might be. Then it began to move about my face — a sensation that I would liken to being gently brushed with eyelashes or a feather. I froze for another moment while carefully planning my next move, then whisked “the thing” off with my hand and bolted across the room to the light switch. I was just quick enough to catch a glimpse of an immense, dark, hairy-looking spider skittering into the crack between the mattress and the back of the sofa. I was not amused. However, there was no place else to sleep, so I turned my sleeping bag around, placed my pillow at the foot of the bed, and undoubtedly spent the remainder of the night brushing away imaginary spiders.

female Dark Fishing Spider (Dolomedes tenebrosus) on cedar fence rail (May 30, 2004)

Fastforward almost half a century. In that span of years, many fishing spiders have come and gone. These days, the sight of a nice, fat, velvety, Dark Fishing Spider (Dolomedes tenebrosus) such as the one above, is always cause for great delight (click on all photos for larger views). Despite its common name, this species is often found wandering and hunting for prey far from water. In fact, most times, I find them resting atop a fallen log, or a cedar fence rail along the trailside. Sometimes, I’ll find one on the wooden dock at a local creek where I launch my canoe. They’re frequent visitors to cottages, a fact attested to by the number of times someone has emailed me a photo of the “gigantic spider” found under the sink or in the outhouse at a cottage.

Dolomedes spider (probably D. scriptus) “fishing” for aquatic prey in a stream (Aug. 24, 2005)

So, why do we refer to the Dolomedes as “fishing spiders”? As the name suggests, this genus of spiders is usually found on or near water, “fishing” for aquatic prey, or other creatures attracted to the water’s edge. Typical prey might include water striders, small minnows and even tadpoles. Spiders such as the Striped Fishing Spider (Dolomedes scriptus) may be found clinging to a rock, piece of wood, or vegetation, with several legs resting lightly on the water’s surface as in the above photo. They wait patiently, sensing the approach of prey through the movement of the water. When something comes within striking distance, they make their move, seizing their prey, and even diving below the water’s surface in pursuit.

Six-spotted Fishing Spider (Dolomedes triton) on vernal pool (May 9, 2004)

A frequently seen species is the Six-spotted Fishing Spider (Dolomedes triton) that may be found floating on the surface of ponds and streams. I often find them floating or gliding about on shallow, vernal pools and in ditches along forest trails.

Striped Fishing Spider (Dolomedes scriptus) resting on a fallen log (May 16, 2004)

The Striped Fishing Spider (Dolomedes scriptus) (above) is another freqently seen species. We’ve occasionally found them while paddling our canoe along the shorelines of creeks where they were resting on exposed tree roots or rocks. They are quite beautiful, having a white stripe running along the sides of the carapace and abdomen. The above spider was found resting on a log near Charleston Lake, just a few centimeters from a Dolomedes tenebrosus. Perhaps they were checking each other out.

a ball of spiderlings found about 30 cm. above the water along the Jock River (July 6, 2004)

Dolomedes spiders belong the to Family Pisauridae, commonly known as the Nursery Web spiders. They are referred to as such because the females construct a spherical egg sac and carry it in their jaws (chelicerae) until close to the spiderlings’ time of hatching. Then, they place the sac inside of a nursery web of silk strands secured to vegetation, and remain on guard close by. After hatching, the young spiderlings remain in the nursery for a time, occasionally moving away from each other, but quickly reforming into a ball when disturbed. I photographed the above ball of spiderlings on July 6, 2004, while doing a stream survey on the Jock River, west of Ottawa. I’m quite certain they are some species of Dolomedes, although I didn’t see the female.

spiderlings moving apart, perhaps in response to sunlight falling upon them (July 6, 2004)

While I watched over the spiderlings for the space of a few minutes, they would occasionally move apart. However, if a cloud passed over the sun, or my shadow fell over them, the spiderlings would immediately reform into a tight ball. I’m not sure if they move apart and back together in response to the slight changes in temperature when the sun is directly on them or in shadow, or whether they are using shadows as a cue that there may be danger close by, and regrouping as a defensive measure.

recently molted Dolomedes spider with exuviae, as found under cedar board (Aug. 12, 2004)
(click on image for larger view)

A final story to wrap up this piece on encounters with Dolomedes spiders. The above spider was photographed along the Cataraqui Trail near Opinicon Lake, on August 12, 2004. A friend, Eric Snyder, and I had been wandering along the trail, turning the odd stone or bit of wood to search for interesting invertebrates. One or the other of us spotted this spider under a small piece of cedar (see above and photo at top of this post). I’m quite sure it was a Dolomedes tenebrosus. It had just recently molted and was quite a bright orangeish colour. The exuviae lay crumpled in a depression in the sand beneath one end of the stick. When I attempted move in with the camera to shoot a few macros, the spider retreated to the exuviae. When I withdrew, the spider would abandon the exuviae, but quickly return to it when I moved in once more. I found that quite interesting and just a little reminiscent of the behaviour of the spiderlings in the little spider ball. Perhaps there’s some sense of safety in numbers, even if the “other” spider is just your own exoskeleton.

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19 Responses to “close encounters with Dolomedes spiders”

  1. Mark Says:

    Very nice pictures. I especially like the striped fishing spider. Although the body doesn’t look much like the background, the legs almost disappear.

  2. Wayne Says:

    Nice piece on Dolomedes! I imagine your bedtime story has installed in many of your readers quite a few nights’ worth of nightmares!

    They are spectacular spiders. I don’t think I’ve ever seen one on the water – usually they’re clinging to a vertical wall.

  3. burning silo Says:

    Mark – Thanks! I like the Striped Fishing spider too. It was actually the white parts that gave it away, and then I noticed the Dark Fishing spider nearby. I find that I see them more by shape recognition than by colour. After you’ve found quite a few, you just seem to notice them, even when they’re well camouflaged.
    -
    Wayne – Ha! I debated with myself over posting that little story in case it initiated any new cases of arachnophobia! (-:
    Yes, indeed, they are spectacular spiders. I see the Dark Fishing Spiders away from water most times, but the Six-spotted always on water. The Striped usually at or near the water’s edge.

  4. Susannah (Wanderin' Weeta) Says:

    Great post!

    “After hatching, the young spiderlings remain in the nursery for a time, occasionally moving away from each other, but quickly reforming into a ball when disturbed. “

    Interesting. Some spiderlings we saw last summer did exactly the opposite: scatter when we moved too close.

    There’s a photo, of sorts (film camera, hardly any zoom) on my old blog, here.

    You’ll have to click on it to get any sort of view; Delphi only allowed those tiny thumbnails.

  5. Mark Says:

    I was checking out the Living the Scientific Life blog and saw a spider picture. For a moment I thought I had accidentally loaded Burning Silo, and then I saw that it was, indeed, your spidey picture. I knew I recognized it.

    Oh, your spider story reminds me of my scorpion stories. There’s the one where a scorpion dropped from a beam in the living room ceiling directly between my bare legs, and the one where I rolled over onto a scorpion in bed. I checked my bed carefully for years after that one.

  6. burning silo Says:

    Susannah – Thanks! That’s interesting about the spiders dispersing when approached. Now I’m wondering if these were just regrouping because they noticed the temperature change when there was a shadow passing over them. Hmmm. Now I’ll have to find more spiderling balls to study and conduct some experiments! Interesting stuff though, isn’t it?
    -
    Mark – Thanks for mentioning that, Mark. I had sent quite a few photos of different creatures to GrrlScientist awhile back and the spider is probably the last of them to appear on her blog. I must round up some more to send along.
    I think that if scorpions fell off of ceilings or I found them in my bed, I’d be checking for them pretty often too! (-:

  7. Celeste Says:

    HI! Those are great spider pictures!!! Made them look pretty. I wonder if there are fishing spiders where I am–I’ll have to check it out(we don’t seem to have many spectacular spiders here–although the webs are pretty). Thanks for all the work in putting that together.

  8. burning silo Says:

    Celeste – Thanks! I just did a quick check to see if I could find out if Dolomedes spiders are found in the PNW. I didn’t find anything that said that they were for sure, but I’d be kind of surprised if there weren’t at least a couple of species out there. I did see a note from someone posted to a message board saying they had seen Dolomedes triton in eastern Oregon. Thanks for dropping by and leaving a message. I found my way over to your blog and I’ll be back to read more.

  9. Dave Says:

    Wonderful photos and posts about a group of spiders i knew nothing about. Thanks! One minor quibble, though: shouldn’t the singular form be exuvia?

  10. burning silo Says:

    Dave – Thanks. For years, I didn’t know much about them other than that they were big. (-:
    Exuviae is one of those words that is the same in both singular and plural (or at least, that’s what my dictionary says). I’m not exactly sure why that would be, but that’s how it usually appears in spider and odonate field guides. Maybe someone reading this will know what rule makes it so.

  11. John Says:

    Bev, keep posting these incredibly informative bits…even for those of us who are, as of now, totally lost with respect to the true science of your observations, they are wonderfully informative.

  12. Duncan Says:

    Great post Bev, thanks.

  13. burning silo Says:

    John – I’ll probably keep on posting them so long as there is someone reading them. (-:
    -
    Duncan – Thanks!

  14. robin andrea Says:

    I’m so glad you searched your archives for these spider pics. They are so beautiful, and the accompanying text incredibly informative. Roger and I have had the same response from the Argiope aurentica spiderlings that Susannah has. They disperse when we come upon them in their nursery.

    Looking at these pics is almost as good as being outside!

  15. WrenaissanceWoman Says:

    Great pictures! I’m wondering if I’ve seen these and thought they were wolf spiders. We recently moved to a home on the edge of a wetland, so I’m hoping that I’ll find some around this summer now that I know what to look for.

  16. burning silo Says:

    robin – At this time of the year, it sure lifts the spirits to look through summer photos. I’ll probably post more like these spider photos very soon. Interesting about the Argiope spiderlings dispersing. Having read what you and Susannah have written, I’m guessing that the spiderlings I watched must have been reacting to shadows and temperature change, and perhaps not perceived the shadows as a threat. Perhaps they would have dispersed if they had thought so. Interesting!
    -
    WW – Thanks! It could be that you’ve seen these spiders and thought they were Wolf Spiders. They are enough alike that they are easily confused. There is a difference in their eye arrangement, but that’s really very difficult to see without some kind of magnifying glass. Also, Fishing spiders tend to rest with their legs really splayed out, but I rarely see a Wolf spider do that — they usually seem ready to move at any second. If you’re close to a wetland, I’d look for Dolomedes triton around vegetation at the shallow edges, and also be checking any fallen trees, rotting wood, etc.. for spiders. I’m guessing that you’ll find some there for sure.

  17. Dave Says:

    A number of online sites do give exuvia, though, including the Free Dictionary.

  18. Filip Says:

    First picture with this text: recently molted Dolomedes spider with exuviae in background (Aug. 12, 2004)
    This is absolutely not Dolomedes, not even a Pisauridae, it’s a wolf spider family Lysosidae.

  19. bev Says:

    Hi Filip – do you think so? It was absolutely huge for any wolf spider species I’ve seen here in eastern Ontario, and I have seen many wolf spiders over the years. This was probably double the size of any species I can think of. Definitely more in the size of a very large Fishing Spider.