Large spiders near waterfront properties, often seen darting across the water or resting on docks and boathouses, are a common concern. These arachnids are generally called “dock spiders,” a common name for several species of Fishing Spiders belonging to the genus Dolomedes. While their size can be alarming, managing their presence requires understanding their behavior and applying targeted methods for immediate removal and long-term environmental control. This guide outlines practical, safe steps to clear your structures of these spiders and prevent their return.
Identifying the Dock Spider and Assessing Risk
Dock spiders are easily recognized by their impressive size and coloration, often exhibiting a leg span that can reach up to four inches; females are notably larger than males. They typically have a brownish-grey body with distinct black and light brown markings, and their legs are often striped or banded. Unlike many other spiders, they do not spin large, intricate webs to catch prey, instead relying on speed and sensitivity to hunt.
These spiders are semi-aquatic, possessing specialized hairs that allow them to walk or glide across the water’s surface. They frequent docks, boathouses, and rocks near water because they use the surface tension to detect vibrations from aquatic insects, tadpoles, or small fish, which they ambush. Despite their formidable appearance and large fangs, dock spiders are generally timid and non-aggressive toward humans.
A bite is a rare defensive action that occurs if the spider is trapped against the skin, such as being accidentally grabbed or sat upon. The venom is mild, intended for subduing prey, and its effect on humans is comparable to a bee or wasp sting, causing only localized pain and redness. The risk they pose is minimal, and their removal should focus on non-confrontational methods.
Immediate DIY Removal Methods
Physical removal is the most direct and effective strategy for dealing with spiders inhabiting your dock or structure. A long-handled broom or brush should be used regularly to sweep the surfaces and crevices, actively dislodging spiders and destroying any newly formed nursery webs or egg sacs. A high-powered vacuum cleaner equipped with a hose attachment offers an excellent, non-contact method to quickly capture individual spiders from hard-to-reach corners and beneath dock planks. Immediately seal and dispose of the vacuum bag or canister contents far away from the water.
A direct, water-based approach can also flush spiders from the immediate area, which is particularly effective near the water’s edge. A strong jet of water from a garden hose or a power washer can physically blast the spiders and their shelter webs away from the structure. This technique encourages the spiders to relocate to natural habitat away from the dock.
To address spiders and their egg sacs, which can contain up to 1,000 offspring, targeted low-toxicity sprays can be utilized. A simple solution of diluted vinegar and water, or water mixed with citrus oil (such as orange oil), can be sprayed directly onto the arachnids or frequently seen areas. These natural substances act as a deterrent and can destroy egg sacs upon contact, but they should be applied judiciously to minimize runoff into the surrounding water.
Long-Term Environmental Control and Prevention
Sustainable control focuses on making the environment less appealing to dock spiders by limiting their access to shelter and prey. A primary preventative measure is removing debris and clutter from the perimeter of the dock and shoreline. Piles of wood, stored equipment, loose rocks, or overgrown vegetation provide ideal, secluded hiding spots for the spiders to rest or build their nursery webs.
Managing the surrounding habitat involves controlling moisture and limiting their food source. Regularly trimming back tall grasses and shoreline plants near the structure eliminates nesting sites and reduces pathways onto the dock. Since spiders are attracted to areas with a high concentration of insects, minimizing outdoor lighting near the water at night will significantly reduce flying insects, cutting off the spiders’ primary food source.
For boathouses or structures with enclosed spaces, sealing potential entry points prevents spiders from sheltering inside. Cracks in the foundation, gaps around utility lines, or unsealed window and door frames should be addressed to block access. If populations remain persistently high despite these efforts, consultation with a professional pest control service may be necessary to implement targeted, environmentally compliant treatments.