About Slugs and Snails

Garden Slug on Leaf

Slugs and snails are probably the most destructive pests in the garden, especially for young lilies and older lilies starting to emerge! They are nocturnal feeders and before you know it, your veggie starts or that prize lily plant Aunt Edna gave you is GONE! They not only feed on lush green foliage of low lying and slow growing vegetables and landscape plants, but also feed below ground on roots. However, they are also beneficial in the fact they feed on decaying material above and below the ground, too. But, unfortunately, they prefer the lush “green” stuff.

Holy cow! There are so many articles on the web, books, videos, etc…about slugs and snails, it’s mind boggling. In order to keep slugs and snails under control (not exterminate because they are beneficial too!) I thought it would be best to understand the critter first…”who, what, when, and why” sort of thing and what makes it tick.

During the last thirty plus years in the landscape pest control business, I found it best to understand just what you are dealing with and maybe there is an alternative measure to take rather than “nuking” a yard with pesticides or poison slug bait. Why is this disease or insect attacking only this cultivar or particular plant? Can the environment or other situations where the plant is located be changed? Can a ph level of a certain plant be adjusted therefore creating a healthier plant so insects or diseases won’t attack it. Can the plant be moved to a different location, is the plant in the right location, i.e. shade, sun? In other words, what alternatives are there to help control or alleviate a problem?

So, after diligently spending the last two months researching these awful, disgusting and destructive pests (as well as fighting them forever!), I have concluded this is the best and most precise, short article on understanding these slimy beasts before getting a handle on controlling them. In the next few weeks, I will put together some good control measures for you to choose from and what I have found works best.

Slugs and Their Management

Slugs are simply snails (mollusks) without shells. These slimy creatures live in and on the ground and have big appetites for a wide variety of plants found around the home. Young seedling plants are eaten as well as mature plants. They frequently cause damage to glasshouse (greenhouse) and garden plants, and may be especially injurious in mushroom houses. Occasionally, they may congregate in large numbers in basements, on walls, doorways, and along walkways, making these areas unsightly. Slugs may be found when the ground thaws in the spring until it freezes in the fall. Wet conditions are ideal for slug development.

Description of Slugs

Probably the best description of a slug is that it is a snail without a shell. They vary in size depending upon the species and measure from 1/4 to seven inches long. They secrete a characteristic slime (mucus) which they leave behind as they move around. These slime trails are silvery in appearance upon drying and is a common diagnostic character used to identify the presence of slugs. The color of slugs also varies with species, ranging from a dark black-brown to an orange color. When an actual slug is found their soft slimy bodies and extensible eye stalks give the creature its characteristic appearance.

The most common slugs found in landscapes are the gray garden slug, the leopard slug, and the dusky slug. The gray garden slug is the most common and is generally a mottled gray to black in color. It is usually less than one inch long. The leopard slug is the largest, commonly reaching four to five inches in length. It has characteristic black spots on its upper surface. The dusky slug is intermediate in size, being one to three inches long, and can range from a gray to a bright orange in color.

The eggs appear as perfectly round gelatinous spheres filled with a watery substance. They range in size from 1/8 to 1/4-inch in diameter. They are usually colorless, often reflecting the color of their surroundings, but they may become cloudy just before hatching. Baby slugs resemble adults but are smaller and may not be as fully colored.

The Development of Slugs

Slug Eggs

All slugs lay eggs. Each species requires a different length of time for the development of its eggs and the maturing of its young. The number of eggs laid at one time by one slug may be up to 100, but average 20 to 30. Young adult slugs apparently lay fewer eggs than older ones.
Though slug eggs may be found outdoors during any month of the year, most of the eggs are laid in the spring and early summer. Most species overwinter as adults or nearly mature young. In the spring, eggs are laid in moist areas and the new slugs normally reach maturity by fall. During periods of particularly warm and wet climatic conditions, the rate at which the slugs develop may allow for eggs to be laid in mid-summer, thus making possible a second generation. Mating usually takes place from August until mid-October and eggs can be laid from 30 to 40 days after a successful mating.

Eggs are generally laid on or near the soil surface, but are usually deposited in places of concealment, such as underneath mulch, dead leaves, rocks, flower pots, trash, and boards. Particularly preferred are spots where the nature of the cover keeps the surroundings relatively cool and moist.

The minimum temperature at which egg development will take place varies with the species of slug but is in the general range of 32 to 42 degrees F. At the minimum temperature, as long as 100 days may be required for the eggs to develop. At higher temperatures, development is usually completed in ten days to three weeks.
As soon as slugs hatch, they are active and begin to crawl or feed if the temperature and humidity are right. They are mainly nocturnal and remain motionless and concealed until nightfall provides suitable conditions for activity.

The rate of growth of immature slugs depends mostly on the type and amount of food available. Dry conditions usually result in a loss of weight which is regained rapidly when moist conditions return.
In a temperate climate, slugs usually live one year outdoors. In greenhouses, many adult slugs may live for more than one year.

Ohio State University Fact Sheet HYG-2010-95

Photos Courtesy of Ohio State University, Wikipedia