Everything You'll Never Need to Know About Slugs
Created | Updated Jan 28, 2002
They walk on one foot. They have antennae. They live in water or on land. Some are very colorful; others are just plain black and brown. Their slime creates an electric current. They come out at night to eat, and only one thing can stop these slippery, boneless blobs: salt. I am talking about slugs. Not aliens, the school lunch, nor taxi drivers. Just plain ole slugs. Land slugs and sea slugs are both interesting animals, and they both share some things in common.
Both land slugs and sea slugs are very unique, although both show obvious relation. The two are both invertebrates (animals without bones), more specifically they are both mollusks (phylum), and even more specifically they are both gastropods (class). Slugs are the only gastropods that lack an external shell, yet some slugs possess an internal shell. Slugs have been compared to their relatives, the snails, quite often. Slugs are said to be very closely related to snails; sometimes they are even called snails without shells. Land slugs and sea slugs mostly feed on vegetation, although some slugs eat other animals, including other slugs. One thing to note about slugs is that they are hermaphrodites, or organisms with both female and male sex organs. In the early process of their lifespan, slugs are males, and as they grow older, they develop the female organs. Slugs do not need a partner to reproduce, yet most slugs use partners to mate. Slugs lay from three to five hundred eggs, depending on the species. This is possibly why slugs are such successful organisms.
Because slugs are so successful, they can be found just about anywhere. Of the approximate forty species of land slugs in North America, thirty species are most commonly described as pests by gardeners because of their consumption of vegetation. Slugs only go out at night to eat, thus making it harder to spot them. During the daytime, slugs can be found in small crevices, and places that are dark and damp. At night when the slugs eat, they can consume several times their weight. They need all the food so they can produce the slimy secretes mucus that they move on.
As you might have guessed, slugs do not move at an astonishing speed. In fact, they only move at a meager 0.025 miles per hour. That’s one mile per 1.6 days, assuming they move at a constant rate. It should be noted that most slugs wouldn’t attempt to “walk” one mile because there is no need to, and if a slug did try, it would most likely die. The reason slugs are so slow is because of their inefficient method of travel. Slugs use one foot to move from place-to-place, and that one foot glides on the mucus given off by the slug. The slug leaves a shiny trail when the mucus dries up. In order to produce enough of this slimy substance, slugs have special secretory granules (cells used to store mucus) that are ten times larger than those of humans. Slugs produce so much mucus, they can make it over a sharp blade unharmed. For some reason unverified in my research, the mucus of slugs reacts to copper in such a way that it creates an electric current. I don’t know what this current can do to the slugs, the copper, or anything else, but wouldn’t it be interesting to see?
There are many species of sea slugs, about 2,500 to give you an idea. Most can be no bigger than two inches, but some nudibranches can be up to two feet long. In the beginning stages of their life, sea slugs don’t look anything like their parents. In fact, sea slugs start out with shells as children, but shortly after birth they lose them.
Most people have classified sea slugs as beautiful animals. This is because of their brilliantly colored bodies. The colors are used as camouflage for protection against predators, but as the slugs move deeper into the sea, the colors become less, intense, making them more visible. That is why most slugs stay near or even on top of the surface of the water the majority of their lives.
Nudibranches have been classified as both herbivores and carnivores, depending on the species. Some herbivorous sea slugs spend almost all of their life next to seaweed or beds of algae. For instance, the Sargassum Sea Slug actually lives attached to sargassum seaweed. Carnivorous sea slugs eat mostly small fish, sea anemones, sponges, worms, barnacles, jellyfish, and hydroids. Hydroids have special stinging cells that sting their predators when they attack, but sea slugs are immune to these stingers. As a matter of fact, when slugs eat the hydroids, the stinging cells are actually passed into the skin of the slug. So when a slug’s predator attacks the slug, it’s stung by the stinging cells of the hydroids. Another thing that sea slugs absorb from the food they eat is the color. If a slug eats something blue, it turns blue. If it eats something brown, it’ll turn brown. This is how sea slugs gain their brilliant camouflage. You are what you eat, right?
Both land slugs and sea slugs are very unique, although both show obvious relation. The two are both invertebrates (animals without bones), more specifically they are both mollusks (phylum), and even more specifically they are both gastropods (class). Slugs are the only gastropods that lack an external shell, yet some slugs possess an internal shell. Slugs have been compared to their relatives, the snails, quite often. Slugs are said to be very closely related to snails; sometimes they are even called snails without shells. Land slugs and sea slugs mostly feed on vegetation, although some slugs eat other animals, including other slugs. One thing to note about slugs is that they are hermaphrodites, or organisms with both female and male sex organs. In the early process of their lifespan, slugs are males, and as they grow older, they develop the female organs. Slugs do not need a partner to reproduce, yet most slugs use partners to mate. Slugs lay from three to five hundred eggs, depending on the species. This is possibly why slugs are such successful organisms.
Because slugs are so successful, they can be found just about anywhere. Of the approximate forty species of land slugs in North America, thirty species are most commonly described as pests by gardeners because of their consumption of vegetation. Slugs only go out at night to eat, thus making it harder to spot them. During the daytime, slugs can be found in small crevices, and places that are dark and damp. At night when the slugs eat, they can consume several times their weight. They need all the food so they can produce the slimy secretes mucus that they move on.
Land Slugs
Land slugs are well developed for their size. They have eyes, the senses of touch and smell, and an astonishing 27,000 teeth in their mouths. Slugs have four tentacles, two of which are for seeing and two for smelling and touching their food. The two larger tentacles on top possess the eyes at the tips, and the two smaller ones near the mouth help the in digestion process. However, the mouth is not used for breathing, instead there is a hole, called the pneumostome, in the side of the body that takes care of respiration. The bigger antennae, for protective reasons, can pull their eyes into the head when the eye or eyes are touched.As you might have guessed, slugs do not move at an astonishing speed. In fact, they only move at a meager 0.025 miles per hour. That’s one mile per 1.6 days, assuming they move at a constant rate. It should be noted that most slugs wouldn’t attempt to “walk” one mile because there is no need to, and if a slug did try, it would most likely die. The reason slugs are so slow is because of their inefficient method of travel. Slugs use one foot to move from place-to-place, and that one foot glides on the mucus given off by the slug. The slug leaves a shiny trail when the mucus dries up. In order to produce enough of this slimy substance, slugs have special secretory granules (cells used to store mucus) that are ten times larger than those of humans. Slugs produce so much mucus, they can make it over a sharp blade unharmed. For some reason unverified in my research, the mucus of slugs reacts to copper in such a way that it creates an electric current. I don’t know what this current can do to the slugs, the copper, or anything else, but wouldn’t it be interesting to see?
Sea Slugs
Unlike land slugs, sea slugs, also known as sea pigeons or nudibranches, are much more admired by people. The first reason is because they are by far more attractive than regular land slugs, and the second and most obvious reason is that they don’t destroy plants and crops. Since they live in shallow salt water, there really isn’t much the sea slugs can ruin in the first place.There are many species of sea slugs, about 2,500 to give you an idea. Most can be no bigger than two inches, but some nudibranches can be up to two feet long. In the beginning stages of their life, sea slugs don’t look anything like their parents. In fact, sea slugs start out with shells as children, but shortly after birth they lose them.
Most people have classified sea slugs as beautiful animals. This is because of their brilliantly colored bodies. The colors are used as camouflage for protection against predators, but as the slugs move deeper into the sea, the colors become less, intense, making them more visible. That is why most slugs stay near or even on top of the surface of the water the majority of their lives.
Nudibranches have been classified as both herbivores and carnivores, depending on the species. Some herbivorous sea slugs spend almost all of their life next to seaweed or beds of algae. For instance, the Sargassum Sea Slug actually lives attached to sargassum seaweed. Carnivorous sea slugs eat mostly small fish, sea anemones, sponges, worms, barnacles, jellyfish, and hydroids. Hydroids have special stinging cells that sting their predators when they attack, but sea slugs are immune to these stingers. As a matter of fact, when slugs eat the hydroids, the stinging cells are actually passed into the skin of the slug. So when a slug’s predator attacks the slug, it’s stung by the stinging cells of the hydroids. Another thing that sea slugs absorb from the food they eat is the color. If a slug eats something blue, it turns blue. If it eats something brown, it’ll turn brown. This is how sea slugs gain their brilliant camouflage. You are what you eat, right?
