of Rhode Island GreenShare Factsheets
Slugs are legless, boneless creatures. They are similar
to snails, but have a raised mantle on the back instead of
the familiar shell. Slugs are nocturnal feeders, hiding during
daylight hours. There are many species of slugs capable of
harming tender landscape plants or causing economic damage
to greenhouse crops and field crops such as crucifers, strawberries,
raspberries, potatoes, tomatoes, beans and lettuce. Most species
survive the winter as eggs or adults. An adult may be a single
sex or have both male and female reproductive organs (hermaphroditic)
and be self-fertile. A single individual is capable of producing
up to 500 eggs, which are deposited in batches of one to several
dozen under stones, debris or in the soil. Eggs usually hatch
in the spring or early summer. The gray garden slug is the
most common and most destructive slug in this area. This 20
mm (3/4 inch) long pest varies in color from whitish yellow
to nearly black, with brown specks and mottling. The tawny
garden slug can reach 10 cm (4 inches) in length. It is usually
recognized by its yellow mantle and lighter spots on a yellow
body. This type is less common than the gray garden or spotted
garden slugs. During wet growing seasons, large numbers of
slugs survive the summer months and may move into gardens or
cultivated fields from weedy borders, drainage ditches or other
moist, sheltered areas. Landscape or crop damage is usually
most severe in late summer or early autumn of cool, wet growing
seasons, especially when preceded by a mild winter.
Slugs feed by grating away the surface of the plant tissue
with a tooth-covered radula, which works like a rasp. This
type of feeding injury is easily distinguished from caterpillar
feeding on thick-leafed cole crops like cabbage. The grating
action produces a large wound on the leaf surface nearest the
slug, which gradually tapers to a smaller hole through the
opposite surface. Slug injury to cabbage appears ragged compared
with the clean-sided incision typical of caterpillar feeding.
On thin-leafed crucifers or other crops, insects produce leaf
injury which is virtually indistinguishable from slug feeding.
The presence of a glistening slime trail can sometimes be used
to distinguish slug injury. Slugs attack the fruit of tomatoes
and strawberries leaving small, shallow holes in the fruit's
surface. Scout for signs of slug feeding on ornamental or crop
plants near the weedy borders of yards and fields.
A covered pit can be used to provide a humid, sheltered
hiding place for slugs during daylight hours. The pit should
be four inches in diameter and six inches deep. An aluminum
foil-covered shingle or a board can be used as a cover to provide
a cool refuge from the sun. Slugs tend to congregate in large
numbers in these shelters and may be counted and destroyed
during daylight hours. Set monitoring traps near field and
garden borders. The traps will not function as well in weedy
areas or with crops such as cabbage which provide adequate
shelter for slugs beneath large leaves close to the ground.
Control measures should be applied when one to five slugs per
trap are found.
- Maintain good weed control within the garden or field
and along borders to eliminate daytime refuges of slugs.
- Slugs avoid crawling over anything dry, dusty or scratchy,
such as lime, road dust, diatomaceous earth, cinders, coarse
sawdust, gravel or sand. Secretion of enough mucus to free
themselves from these materials soon exhausts them and they
die. A border of any of these inert materials, therefore, helps
control slugs. It is also reported that hydrated lime, Bordeaux
mixture or urea repels slugs. Remember, however, lime affects
the pH of soil. Never use salt, as it ruins soil for most plant
- A fly screen, 4 inches wide, placed on edge and partly
embedded in soil for support, will keep slugs out of an area.
Boards, bark, or other materials not less than six inches square
make effective traps when placed in gardens. Each morning you
can gather the slugs from under the traps and destroy them.
Slugs can also be hand-picked off garden plants at night using
a flashlight and a pair of disposable gloves. However, since
only a portion of the population is active on a given night,
it can take quite of bit of slug harvesting before there is
a noticeable impact on the population. Slugs can be kept from
potted plants by supporting pots over a pan of water.
- Slugs are attracted to and drown in a shallow dishes
containing beer or baker's yeast dissolved in water. Set the
top edges of the dish at ground level and cover loosely with
a board so slugs can easily get into the mixture.
- Choice of mulch can have a large impact on slug problems
in flower gardens. Large bark chips and wood chips provide
excellent hiding places and favor slug outbreaks. Shredded
pine bark is less attractive, and cocoa hulls seem to repel
- Toads are the most important natural enemy of slugs.
Many people also claim that several ducks keeps a garden slug
Chemical control is generally not recommended for homeowners.
Although baits containing Metaldehyde can be quite effective
in slug control, they are toxic to dogs and may represent a
hazard to children. Use of this material is also prohibited
after edible portions of vegetables begin to grow.
Adapted from the University
of Connecticut Integrated Pest Management Program and the
University of Maine Cooperative Extension, 1999
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program