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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