Fishing Spiders 101

"Eek...They're Big Enough to Saddle Up and Ride!"

Have you ever been near the water's edge and seen very large spiders that are hanging out in or on the water? If you're in the Eastern United States near fresh water or brackish water, then you've most likely met the common fishing spider also called dock spiders or wharf spiders. At our rowing boat house we call them launch spiders too. In part this is because they like to ride in our launch boat and if you hit high speeds in that launch boat they tend to "launch" themselves at you when they lose their footing (which our fearless coaches can attest to!). Fortunately, fishing spiders are very harmless and quite skittish despite their size (ranging from 1-3").

Fishing spiders belong to the genus Dolomedes (dole-o-me-dees) in the family Pisauridae (fizz-our-i-day), and compared to other tiny spiders they look big enough to carry off small children (when actually they eat small bugs, tadpoles, and other invertebrates). There are 100+ species of Dolomedes world wide but 8 that are common in the US. These include (using my common names and Latin names):

• Six spotted fishing spider (D. triton, all of N. America, Canada, S. Alasaka)

Notice the beautiful abdomen with white trim and six distinct spots. They also have a distinct white edge to their cephalothroax (fused head-throax). Their legs are light colored and can often look palish green to striped or even spotted with yellow markings. Females can be up to 2.5' long and males are usually much smaller, up to  1/2" long.

• Common fishing spider (D. tenebrosus, E. US and S. Canda)

These beauties range from up to 1" for females and 1/4" for males. They like woodland areas and especially trees. They're also more common in houses than the other types of fishing spiders. Much like the "W" or "Writing" spider they have inverted 'W's on their abdomens (often whitish in color). The females are always larger and practice male cannibalism, much like praying mantises. The weird thing is that the male spontaneously dies after mating with the female (she doesn't kill him), offering himself up as post-sex snack. Click here if you really want to see a movie of it!

• Striped fishing spider (D. striatus, found in N. US and S. Canada)

Here you can see the "stripes" on the abdomen of the striped spider. These tend to be a bit more light brown to tan, with a dark stripe down their abdomen (ranging from mahogany to dark brown), with lighter stripes running horizontally. They too have a set of white stripes along the edges of their cephalothorax.

• Fishing spider (D. vittatus, E. US and SE Canada)

D. vittatus are the quintessential "saddle up and ride" spiders. They are big, up to 3" in size. These have a dark spot on their upper cephalothorax. They also tend to have six whitish spots on their tapered abdomen. D. vittatus can also come in a dark phase color almost smoky quartz to dark grey. These are more common in N. Carolina.

• "Writing" Fishing Spider (D. scriptus,  E. US and S. Canda)

These are also very common and large spiders, and they tend to scare the heck out of people because they look somewhat like wolf spiders. However, they are still quite harmless and shy. I call these the "W" or "writing" fishing spider because of their Latin name, scriptus, meaning "script" or "write", and the "W" pattern on their abdomen.

These last three are less common in our region, so I'm not going to focus on them here. If you want good pictures and information then visit the Bugguide.net.

• White banded fishing spider (D. albineus ,found in the S.E. US)
• Okefinoke fishing spider (D. okefinokensis, found in Ga and Fla)
• New Mexico fishing Spider (D. gertschi, only in AZ and NM Gila River area)

 

Alright, so they're big scary fraidy cats, but how do they hunt? They hunt by sensing vibrations. Their whole body, and especially their legs, are covered with tiny fine hairs. These hairs are hydrophobic (they repel water). I love the "scienc-y term" for this, it's called cuticular hydrophobicity (you can wow friends with that one at parties).  The hairs allow fishing spiders to literally "walk on water." They can either sit and wait or run across the water's surface and get their prey. If you see one sitting, it usually has a pair of legs stretched out before it.

When the spider stretches out like this it is "feeling" the water for vibrations and the movement of prey. Their hairs (also called trichobothria [trick-o-both-re-a]) can tell them how far the prey is and in what direction. Their body hairs can also be used to capture air bubbles and make the spider buoyant under water; meaning they can go short distances below the surface to catch their prey. Fishing spiders are fastidious about keeping their bodies clean, like ducks or other divers, because their hairs need to maintain their hydrophobic properties.   However, unlike ducks,  they don't use oils.  Instead,  their hairs have  a waxy coating to keep them waterproof.

Despite the fact that fishing spiders look scary, they really are beneficial friends around bodies of water. At worst, if they ever chose to bite, it would be about like a bee sting, but nothing major. Regardless, take the time to observe them and to appreciate the ecological services they offer to us, keeping us insect and pest free.