Snails and Slugs

Slugs and Snails

"Even a snail will eventually reach its destination".
- Gail Tsukiyama

introduction

Snails and slugs are terrestrial gastropod mollusks, differentiated by the presence of a shell in most snail species. They have a strong muscular foot, and use mucus to enable them to crawl over rough surfaces and to keep their soft bodies from drying out. They have two pairs of tentacles on their heads for optical and sensory purposes. Land snails will form their shell in their larval stage, and when they are active, all of their vital organs remain inside the shell. They do not shed their shell over time. Instead, the shell grows along with them, requiring calcium carbonate along its edge to grow. Snails will seal their shells with a dry layer of mucus called an epiphragm when they are dormant or in hibernation. In slugs, the part where the shell would form (the mantle) is still there, and is a visible area behind their heads. The common life span for slugs is between 1 and 6 years, and that of snails is between 2 and 3 years (10-15 years if kept in captivity).

Snail and Slug Behavior

All land slugs and snails are hermaphroditic, meaning they can mate with any other individual. Snails lay pearly white eggs in holes in soil, and can produce 6 broods per year. It takes about two years for snails to mature after they are born. Slugs lay translucent eggs, and their young mature in 3 to 6 months' time. Snails and slugs are most active at nighttime, or on cloudy or foggy days when humidity is high. On sunnier days, they take refuge in shady areas and plant debris piles.

Slug eggs with almost fully-formed slugs inside.

Baby snails have shells that grow with them as they mature.

Snails and slugs leave trails that are shiny and noticeable.

When they move around, these organisms use mucus as protection from damaging friction and to lubricate locomotion. During cold weather, they will hibernate in the topsoil of the garden space, but in temperate areas that have mild winters, they are active year-round. They feed on a wide variety of living plants and decaying plant matter, creating irregular holes with smooth edges on leaves and flowers by scraping them with their tongues.

Mollusk Species

There are countless species of slugs and snails that live in a variety of habitats worldwide, including in fresh and salt water. The following list includes commonly seen land species of both snails and slugs that are common pests in gardens.

Cornu aspersum
(Brown Garden Snail)
Snails with brown shells that have yellow and dark brown markings. Body is soft, grey-brown.

Deroceras reticulatum
(Grey Garden Slug)
Native to Europe, North Africa, and Atlantic Islands, these slugs are now present in almost every habitat around the world. They are grey with mottling, and up to 2.4 inches long.

Lehmannia poirieri
(Banded Slug)
This slug species has a worldwide distribution, and are grey, up to two inches long when mature.

Lehmannia valentiana
(Three-Band Garden Slug)
This slug species has a worldwide distribution, and are grey, up to two inches long when mature.

Limacus flavus
(Tawny Slug)
These slugs have yellow bodies with grey mottling.

Milax gagates
(Greenhouse Slug)
These land slugs are dark grey to black with lighter sides. They can reach up to 2 inches long.

Theba pisana
(White Garden Snail)
This species is native to the Mediterranean, but is an invasive species in many areas worldwide. Shells are light colored with brown spiral markings.

Snails and Slugs in the garden

Snail damage to foliage.

Snail damage to a Strawberry.

Snails are common pests of citrus trees.

Slugs and snails are notorious garden pests, preferring succulent foliage and flowers. They primarily feed on seedlings and herbaceous plants, turf grass seedlings, and ripening fruits that are held close to the ground, such as strawberries or tomatoes. They will also feed on young plant bark, foliage and the fruit of some trees. Citrus trees are especially susceptible to snail and slug damage. A good snail and slug management program is comprised of a combination of methods, including:

Eliminate Hidey Holes
These organisms hide during the day to avoid water loss, preferring to spend their hours in boards, stones, debris piles, and in weedy areas around the base of tree trunks. They also hang out in leafy branches close to the ground and amongst dense groundcovers such as ivy.

Give Them a Hand... Pick
One of the best ways to cut down on a large part of a snail or slug population in any given area is to venture out into the garden when they are most active, and physically pick them up and place them in a bucket of soapy water. At first, try to go out every few days, and once a good number of the population is taken care of, picking activities can be done once a week.

Plant Right
Using a variety of plants in the garden that are susceptible and resistant to snails and slugs can be a great way to discourage their presence. If there is no food for them in the garden, they will leave. Plants with highly-scented foliage are perfect, such as lavender, rosemary, or sage. Ferns, Cyclamen, Lantana, Nasturtium, and California Poppy are also great choices.

Use Protection
Because snails and slugs love the succulent foliage of many vegetable garden plants (not to mention the very appetizing fruits that come along later in the season), one of the best ways to deter them is to physically protect them with barriers. Placing plastic bottles around developing seedlings is a great protection option, as are mesh bags. During the daylight hours when snails and slugs are not active, the physical barriers can be removed.

Set Shelter Traps
These pests can be trapped beneath boards and flower pots that are positioned throughout the landscape. They make great hiding places for snails and slugs during the day, meaning that all a gardener needs to do is pick them up, flip them over, and pick them off by hand. Place the slugs and snails in a container filled with soapy water.

Let Them Drink Beer
Another way to trap these garden pests is by partially burying a cup filled with beer close to where snails are munching on plants. Snails will be attracted to the smell, come to investigate, and fall in. Sometimes, a top is needed (with holes) to prevent the snails and slugs from simply crawling back out. For the most part, however, they will drown. The beer should be replenished as often as necessary to keep the trap functional.

Barriers to Entry
There are various barriers used to keep slugs and snails out of certain garden areas, the best being copper flashing and screen. When the slime that snails and slugs secrete comes into contact with the copper, it causes a disruption in their nervous system similar to an electric shock. Use the copper foil or tape around planting boxes, tree trunks, containers, or buried partially in soil around the base of a plant. Barriers of dry diatomaceous earth can also work, heaped about an inch high and 3 inches wide around the edge of containers. It is not effective if it becomes damp, however, so it is difficult to maintain.

For non-chemical options and natural pest control methods, consult the Pests and Pest Management page:

Pests & Pest Management