This is what nightmares are made of

I’m going to say it, dock spiders are super scary!  Whenever my kids come running to me because they were frightened by a dock spider, I’m secretly hoping it’s long gone by the time we go back to see where it was.

My Ontario cottage is no stranger to dock spiders who, despite their name, are found all over and not just on docks. Dock spiders are widely distributed throughout cottage-country in Canada and the United States. Whether your cabin is in Michigan, Wisconsin, Minnesota, Manitoba, Ontario, Quebec, or any other lake-country area the dock spider is a regular and feared companion at the cottage.

Whether it’s finding one of these hairy creatures nestled up in your towel, being met on the swim ladder by one as you are about to climb out of the water, or just having one pop up unexpectedly from between the dock boards as you walk to the boat, the dock spider has the ability to strike fear into the hearts of all but the hardiest of souls.

Just remember, dock spiders are more afraid of you than you are of them.

Here are 20 facts on the dock spider that will help to keep you up at night.

1. They are Canada’s Largest Spiders

With nine species found in North America, they range in size but can grow up to three inches across—about the width of your hand. Dock spiders are the largest in Canada. Females can grow to be more than 3.5 inches in length.  People seem to (erroneously) associate size with danger when it comes to spiders.

2. They don’t just live in docks

Although they will feed on a variety of insects and bugs and can also be found on cabins, sheds, outhouses, outdoor showers, or even in the outhouse, dock spiders are typically found on docks because it’s their best hunting ground.

Dock spiders, as their name suggests, tend to be associated with the margins of lakes, ponds, swamps, and rivers, where they typically sit motionless on tree trunks, rocks, boats, and docks.

3. The ones you see on your dock are usually female.

Big female dock spiders tend to be the ones we see most often on the dock. This is their prime territory for hunting aquatic insects, minnows, tadpoles, or any other meal that happens to float or swim by the spider’s hiding place.

4. Dock spiders use venom to paralyze their prey

Dock spiders don’t make webs to catch their prey. They actually stalk out their prey and that’s when they insert the venom to paralyze it and then eat it. They are rarely aggressive towards humans, and a bite is not dangerous unless you are allergic.

5. They have water-resistant legs

Dock spiders’ legs are coated in a waxy substance. Combined with surface tension, this prevents them from being pulled down into the water.

6. They HUNT!

As if they weren’t scary enough, dock spiders are skilled hunters.

They don’t spin webs to catch their prey. Instead, they stalk their victims, capture them using their front legs, which are equipped with several small claw-like appendages using two large fangs to inject them with venom, paralyzing them. This is the primary reason that their vision has to be so sharp.

Don’t worry though, despite their fearsome size, their cuisine of choice doesn’t include human flesh

7. They lay a lot of eggs

One egg sac can hold up to 1,000 baby spiders.  Females can then go on to produce a second, or sometimes a third egg sac before the end of cottage season. Remember one egg sac can produce over 1,000 spiderlings. As amazing as this fact is, we’ll understand if you get grossed out. 

Dock spiders are members of the family Pisauridae, commonly known as nursery web spiders. Female spiders in this family make excellent mothers. They carry their large silken egg sacs around in their jaws until the spiderlings inside are just about ready to emerge. I assume this means that females don’t eat at all during this time!

8. They spin webs to protect their young

Also known as a nursery web spider, dock spiders reserve their silk for spinning egg sacs, which the female spider carries in her fangs underneath her body like a giant cotton ball.

The female spider chooses a safe place for the egg sac and surrounds it with a protective web.  Avoid these at all costs if you want to sleep at night.

She then stands guard by the web until the baby dock spiders hatch.

Once they hatch, the young spiders live in a protected place, typically spun in and among grasses, low-growing vegetation, or between rocks around the margins of water.

9. Sometimes the females eat the males after mating

The male doesn’t die due to the female eating him, it’s actually when he expels his pedipalps his hemoglobin(Spider blood) pressure changes drastically throughout his body, and shortly after he dies.

It isn’t uncommon for the female to devour the male after mating is completed, and in light of this fact, the male has been known to bring along a sacrificial fly as a gift for his lady in an effort to take the edge off her hunger before starting the courtship rituals. Unfortunately for the male, the presentation of gifts doesn’t always save him from the potentially nasty fate that awaits him as the female may eat him anyway to provide nutrients for healthy offspring.

10.  They are also known as Fishing Spiders among other things

The scientific name for a dock spider is Dolomedes. It belongs to the Pisauridae family of spiders. In Canada, this spider is usually referred to as a dock spider. In the United States it is often called a fishing spider. Other common names include wharf spider and raft spider and nursery web spider.

11. They eat tadpoles

While hunting, fishing spiders typically rest with their back legs on floating wood or vegetation, and their front legs resting lightly on the water’s surface. Sensitive leg hairs help them to differentiate between a leaf floating on the water and lunch, allowing them to locate potential prey. If the spider detects a fish under the water, they use their back legs to push off and dive after it.

They catch and consume everything from insects to tadpoles to minnows—making them one of the few invertebrates that eat vertebrates.

12. They can walk on water

Not only do these spiders fish from the edge of the shore, but they also have the ability to run across the surface of the water in pursuit of prey.

They can do this because they have water-resistant legs which are covered with a wax-like film so their feet do not get wet and their weight is distributed in a way that the surface tension of the water is not broken.

13. They can jump on water

In addition to being able to walk on water, they can also jump straight up in the air, from the surface of the water, to avoid swimming predators, such as bass. These amazing aquatic feats are possible because of those legs we talked about earlier that have a waxy surface that is hydrophobic (or resistant to water) and does not become wet when in contact with water.

14. They can Scuba dive for up to half an hour

A dock spider can actually swim underwater and stay submerged for several minutes. It uses air bubbles trapped in the fine hairs on its body under its belly to provide oxygen while it is underwater. Essentially, the spider performs a type of scuba dive.

They are able to breathe underwater because spider lungs are located on the abdomen, which is covered with fine hairs that trap air, forming a sort of diving bell so they’re able to stay submerged underwater to hide from predators or to catch prey. The trapped air makes them very buoyant and if they do not hold onto a rock or a plant stem they float to the top where they pop onto the surface, completely dry.

Dock spiders can survive being submerged in water for up to 30 minutes. So, before you dive off the dock to avoid them, remember that they might be in the water, too…I’m not scared, you’re scared!

15. They only bite when threatened

Like most spiders, dock spiders do use venom to paralyze their victims. A dock spider has large enough fangs to break the skin, but a bite is not dangerous to humans unless the person has an allergic reaction to the bite.

Dock spiders are generally not aggressive toward humans and will usually hide when we approach. A dock spider will only bite a person in the rare situation that the spider feels threatened, for instance, if the female spider is protecting its young.

So, unless you grab the spider or inadvertently step on it, you will likely never be bitten.

16. They Hibernate (in houses sometimes)

Dock spiders are not common household pests. They can however find their way into homes, boathouses, boats and even swimming pools located near their preferred habitats.

However, some spiders are known to travel a distance from water, and are the reason for many alarmed people describing hairy monsters in their basements. This mainly occurs in the autumn months when the spiders are searching for a warm place to spend the winter (under stones, leaves, or bark, or inside buildings).

17. They have two rows of eyes

Dock Spiders are often mistaken for wolf spiders and vice versa. Dock spiders have 2 rows of eyes of about the same size that turn up slightly, while the wolf spider, by comparison, is smaller and has three straight rows of eyes of different sizes.

19. They love to tan

Dock spiders tend to hide in corners and crevices during the daylight hours and come out at night to do their hunting. This is their primary defense mechanism against their main predators; birds, snakes, fish, and frogs.

But also being cold-blooded invertebrates they do enjoy sunning themselves on logs, rock, or docks on warm sunny days but are very skittish and will usually run away or hide when approached.

20. They eat Big

Another amazing fact is that they can consume prey as large as almost 5x times their own size!

You Should Just Let them Be

Dock spiders cause more fear due to their enormous size and their ferocious appearance. They do not cause damage to property or harm people.

We advise against attempting to remove dock spiders or detach an egg sac from a spider by hand. This significantly increases the chances that you are bitten. Attempting to use chemicals and sprays around or on the water to eliminate dock spiders is also advised against as this poses a serious safety risk to you and the environment.

Signs of dock spiders include the remains of large exoskeletons and tent-like nursery webs in and around plants or even attached to manmade structures. Tips for helping to keep dock spiders away from your home include the following:

• Remove piles of rock or wood debris around your home, sheds, or boathouses to eliminate possible locations for shelters.
• Keep all shoreline plants trimmed to eliminate nesting sites and possible hideouts.
• Remove or minimizing any standing water on your property where possible.

If you think your property is infested with dock spiders or have an uncontrollable, intolerable infestation, reach out to a licensed pest control company. They have the expertise to help you safely control and treat a dock spider infestation.

So the next time you come across one of these gentle giants, rather than going with your first instinct to whack it with a broom or crush it with your shoe, let it be and observe it for a while. You might even gain a new-found respect for these creatures and you may be entertained at the same time. It’s especially fun to do this when sitting down at the dock, when the evening comes, having a glass of your favourite beverage.

If you enjoyed this post, check out more of our water’s edge articles.

Frequently Asked Questions about Dock Spiders