Back to HomeOutdoors in the Land O'lakes - June 25, 2009

Dock Spiders

by Steve Blight
Dock Spider

With its hundreds of lakes and thousands of kilometers of shoreline, the Land O’ Lakes area is prime cottage country. And what would an escape to a cozy cottage on the shore of a beautiful lake be without an encounter with a dock spider? At our cottage on Bobs Lake, I generally have a pretty relaxed attitude towards the critters that we share our lakeside retreat with. However, when I encounter a dock spider on my way across the dock to the water for a quick dip, I like to keep a respectful distance.

This is mainly because dock spiders can be very, very big. The dock spiders found in our part of the world are members of the species known to scientists as Dolomedes scriptus. They are by far Ontario’s largest spiders, sometimes growing as large as 10 centimeters across – about the size of a CD! This giant, dark brownish-gray spider belongs to a larger group of spiders known as fisher or nursery web spiders. Female spiders in this family carry their egg sacs containing as many as 500 eggs in their fangs for up to three weeks. Many species then construct a 'nursery' by weaving a few large leaves together with silk. They place the egg sac inside and guard it by resting on the leaves. Most females live long enough to make a second egg sac or occasionally even a third.

Dock spiders actively hunt at night along lakes and ponds, mostly for insects like water striders. Often resting with their front two or four legs on the water, they wait until insects, tadpoles or small fish move and vibrate the water in a certain way, then lunge forward and grab their prey with both legs and fangs simultaneously. Sometimes, this hunting technique takes the spiders below the surface of the water. They will also submerge themselves when frightened. Air trapped in body hair allows them to breathe underwater – up to 45 minutes according to some sources.

As a general rule, dock spiders are not considered aggressive. Like nearly all spiders, dock spiders have a pair of venom glands that lead to their fangs. In this family the venom is effective in paralyzing or killing prey, but it is generally considered harmless to humans. In extremely rare cases, however, individuals may have a medically significant reaction to a bite, so care should be taken, and most sources recommend against handling dock spiders.

I have no objections following the “do not handle” recommendation to the letter. However, I find these creatures fascinating, and I recall one time seeing a female laden with her round egg sac on our dock. Curious, I lowered my head to have a better look at her, and I put my hands down on the dock to support my weight as I peered at her. Perhaps it was her maternal instinct, or perhaps she didn’t fancy my manners, but as I shifted my hands to get a better look at her, she made a beeline for my left hand in what struck me as a full frontal attack. I quickly lifted my hand and she changed direction and went for my right hand, whereupon I decided that she was the better man (so to speak) and beat a hasty retreat.

I no longer plan to get up-close and personal with these substantial arachnids, but I still enjoy seeing them from a healthy distance, and I like knowing they are there, happily going about their business. They will always be welcome along my shoreline!


Please feel free to report any observations to Lorraine Julien at naturewatching@gmail.com  or Steve Blight at natureobservations@rogers.com