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How to Get Rid of Slugs Under Your Deck

Backyard view of grey rambler house with upper and lower decks.
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Slimy, soft-bodied slugs are moisture-loving mollusks that are drawn to damp and sheltered locations around the house. Unfortunately, this love of out-of-the-way places means many homeowners end up fighting slug infestations under their decks where temperatures stay cool during the day.

Although slugs don't usually cause damage to structures, they can destroy plants, and some carry potentially harmful diseases. So getting rid of them is not merely a cosmetic concern. Learning how to get rid of house slugs takes patience and perseverance, but it is simple to do with the right equipment.

Using Chemicals to Control a Slug Infestation

Salting slugs is perhaps the best-known chemical control option, but it is far from the most effective.

Iron Phosphate

Iron phosphate baits are a safe and effective organic option that can be used around children and pets. However, this approach can take up to a week to kill the slugs, according to the University of California Integrated Pest Management Program.

Ferric Sodium

Another option is to use baits containing ferric sodium, which work in as little as three days but are not as safe to use as iron phosphate baits. Both options may need frequent replacement until the slug infestation is resolved.

Metaldehyde

Baits containing a chemical called metaldehyde are highly effective against slug infestations but should only be used as a last resort, warns the PennState Extension website. These baits work by destroying the slug's mucus production, which inhibits their mobility and ability to digest food.

Metaldehyde-based slug baits pose a risk to dogs and children because they are extremely poisonous, so they should only be used if the area is strictly off-limits to all people and animals.

Warning

Baits containing the chemical metaldehyde are poisonous and should not be used in areas near children or pets.

Making the Environment Less Attractive to Slugs

Cultural control of slugs comes down to making the environment less attractive to them but also includes ways of trapping and removing the pests when they appear.

Drying Out the Surrounding Soil

The spaces under decks provide ideal habitats for slugs because they are dark, damp and cool. So applying cultural control to the space should focus on drying out the soil and removing any places where slugs like to rest.

Adjusting how plants surrounding the deck are watered will help reduce the moisture levels under the deck, making the area less attractive to slugs and snails.

Removing Items That Provide Slugs Shelter

The University of Florida IFAS Extension recommends removing any mulch, leaf litter, pieces of wood or large stones that provide shelter to slugs.

Also, inspect under the deck for any loose boards or flashing and nail it down. Turn off drip irrigation around the deck to limit moisture input, and switch to hand watering in the morning so that the excess moisture can evaporate during the day, making the space less hospitable to slugs over time.

Warning

Be sure to use gloves when manually removing slugs, as some species are known to carry infectious diseases.

Manually Removing Slugs by Hand

A necessary part of dealing with a slug infestation under a deck is manual control, which involves removing or destroying the slugs by hand.

Using Cardboard for Easy Removal

Placing a sheet of cardboard on the ground under the deck provides a place for the slugs to congregate; you then lift the cardboard the following morning, scrape up the slugs with a shovel and throw them in the garbage.

Clemson Cooperative Extension recommends placing bait such as cabbage or potato pieces beneath the cardboard to lure the slugs.

Spreading Cat Litter or Diatomaceous Earth on the Ground

A layer of diatomaceous earth or cat litter spread beneath the deck will discourage slugs from gathering by making the ground dry, dusty and difficult for them to crawl over—but it must be replaced often to keep it dry.

Setting Out Beer Traps

Another method of trapping slugs for disposal is to fill a shallow tray or container with beer, which the slugs will crawl into and drown.

It is a good idea to wear gloves when touching slugs, because some species have been found to carry rat lungworm disease, according to the University of Florida Department of Veterinary Medicine.

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