Spiders, Wasps and Insects on Your Boat: Prevention and Safe Cleanup

Know who aboard is allergic. Wear long sleeves and pants, gloves and glasses. Work slowly and stay calm; swatting makes wasps sting, and University of Maryland Extension notes that some wasps release a scent that calls in nestmates. Do not shine a light into a nest entrance. If you cannot see into a crevice, do not reach into it.

Insect nests in the wrong hole can stop an engine or cause a hazard. At the start of the season, and after long storage, check:

• Fuel tank vent on the hull side. Boating Magazine points out that an insect nest or wax partly blocking it can make an outboard hard to start or keep running.
• Holding-tank vent. BoatUS says mud daubers love to nest in vent lines; a blocked vent makes the head smell and can even damage the tank during pump-out.
• Outboard telltale (the "pee hole"). A weak or missing stream with a normal temperature gauge is often a blocked outlet. Clear it gently with a thin wire or zip tie (see the engine overheating guide).
• Bilge blower and engine room vents, and the cowl vents on deck.
• Fire extinguisher nozzle, horn, and any small tubes such as a speed sensor.

Clear nests with a plastic tool, a pipe cleaner or a gentle blast of water. Never push debris deeper into a fuel vent, and do not use compressed air into fuel or holding-tank vents.

University of Maryland Extension calls knocking the nest down the best way to control mud daubers, and they are not aggressive. Pop the nest off with a plastic scraper held flat, catch the pieces in a bag, then wash the spot with boat soap and water. A dried mud stain usually comes off with soap and a soft brush; do not use abrasive pads on gelcoat. A nest with small round holes is old and empty; one without holes may still have young inside.

• If the nest is out of the way and nobody is at risk, you can leave it. UMD Extension explains that social wasp colonies die off each winter and old nests are not reused, so a nest found in fall will be empty after a hard frost and can then be scraped off.
• If it has to go, UMD suggests that sprays or dusts are a last resort. Use a product labeled for wasps, follow the label exactly, and keep it from drifting into the water. Treat late in the evening or early morning when wasps are less active, from as far away as the product allows, and give the treatment time to work before you remove the nest.
• Call a pro for nests inside lockers, hollow spaces, the boom, or anywhere you would have to reach in, and for any yellowjacket or hornet nest, or if anyone is allergic.

Fresh webs come off easily with a soft broom or duster and a rinse of fresh water. Work from the top down (T-top, radar arch, canvas frames, then rails and deck) so debris falls onto areas you have not cleaned yet. Weekly brushing during bug season is far easier than one big scrub.

Droppings and squashed insects leave dark spots that can stain if left in the sun.

1. Rinse with fresh water to soften the spots.
2. Wash with a pH-neutral boat soap and a soft sponge or microfiber.
3. For stubborn marks, use a cleaner made for gelcoat and test it on a hidden spot first.
4. Rinse well and dry. A fresh coat of wax makes the next cleanup much easier.

Skip abrasive pads, scouring powder and strong solvents: they dull gelcoat and can damage striping and decals.

Follow your fabric maker's instructions. For Sunbrella marine canvas, the company recommends brushing off loose dirt, hosing down, washing with water and a mild soap using a soft brush, letting it soak, rinsing until no soap remains and air drying. Sunbrella offers a stronger diluted bleach mix for stubborn stains and mildew, but bleach should not run into the water, so do heavy cleaning off the boat where you can. Clear vinyl (isinglass) scratches very easily: rinse first, then use only a cleaner made for it and a soft cloth.

Lighting is the biggest lever you have. Nocturnal insects are drawn most strongly to UV and blue-white light. Texas A&M suggests yellow "bug" bulbs or low-UV lights, and UMD notes that warmer-colored LEDs attract fewer insects than bluish-white ones. Turn off dock and deck lights when you do not need them, or switch to motion-sensor lights. Fewer insects at night means fewer spiders hunting them.

• Keep food, sugary drinks and trash sealed or take them home. UMD notes foraging wasps are drawn to sweet drinks, fruit and even meat, especially in fall.
• Rinse fish blood, scales and bait off the deck and out of livewells after each trip.
• Close hatches and ports, use screens if you have them, and keep the boat cover snug and in good repair.
• Use the boat. Boats that sit untouched for weeks collect the most webs and nests.

Ants usually walk aboard on dock lines, power cords and fenders touching the dock. Keep lines and cords from resting on bushes or the ground, keep food sealed, and wipe up crumbs and spills. If ants have already moved in, enclosed bait stations used inside the boat are a tidier option than sprays; follow the label and keep them away from children and pets.

Spraying the outside of a boat over water can kill fish and other aquatic life, and many household products are not labeled for use near water. Texas A&M notes that residual insecticides on structures give only temporary relief and should not be used close to water. Peppermint oil, dryer sheets and similar tricks are popular in boating forums, but there is little evidence they do much. If you have a serious, recurring problem, a licensed pest control company can choose products that are legal to use around water.

When you take the boat out of storage, add these to your checklist:

1. Look inside the cover and canvas for nests before you fold it.
2. Check every vent, the telltale, the extinguisher nozzle and the horn.
3. Open lockers carefully and look before reaching in.
4. Brush and wash the boat, then wax the gelcoat.
5. Note where nests keep appearing so you know where to look first next year.