talking points for nature guides
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Phylum Mollusca > Order Gastropoda > sea slugs
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For nature guides: introducing slugs
updated Oct 2016

Don't step on the slugs!
A rock with onch slugs make a good 'first station' to sensitise visitors to the fact that every inch of the shore is alive.

What are slugs?

Have you ever seen a slug? How about a snail? Yes, almost everyone knows what a snail looks like. Slugs are like naked snails! Snails without shells.

Slugs belong to a group of animals called molluscs. Other molluscs include snails, clams, octopus, squids and cuttlefishes!

A closer look at slugs

  • Let's look at this Onch slug! You can almost always find some kind of onch on a rocky shore, even on sea walls. You can do this even in a shelter during rainy weather or while waiting for the tide to go down.
    • How many onchs can you find? "I can see 5, can you see them? See how well camouflaged they are, so watch your step when you walk on the stones."
    • What do you think the onch eats? "Yes, it eats this fuzzy stuff that grows on the rocks. This is tiny seaweed. See the bare patch where it has grazed the seaweed. And see the trail of 'processed seaweed' behind it!"
    • Oops, I dropped the onch. Let's pick it up and put it back where it was. Slugs are slow and if we leave it there it might not be able to get back where it is safe, or it might get washed away when the tide comes in.

  • Wow! We've found a nudibranch! (Pronounced 'noo-dee-brank' to rhyme with 'bank'). Nudibranch means 'naked gills'. After explaining some of its features, put it back exactly where it was and explain why this is important. Many nudibranchs only eat a particular kind of food (usually a sponge or other immobile animal).

  • Why do you think nudibranchs are so pretty and colourful? These naked slugs don't have a shell to hide in. Many protect themselves with chemicals that taste bad, or with stinging cells. They advertise their unpleasant nature by being very striking.

Slug myths to dispel

  • Slugs should not be kept in home aquariums. Many only eat a particular kind of food. If you can't provide them the food, they will die. Or they may eat up their tank-mates. Some produce powerful toxins that can wipe out the entire tank.

Handling tips

Where to find slugs? Onch slugs are common on big boulders, sea walls, even some jetty pilings. Especially those covered with algae. They are more active during a cool day.

Be gentle! Onchs can be very slippery. If one falls it may not be able to creep back to where it's safe. Pick up any dropped onchs and put them back where you found them. Explain why you are doing it.

Don't disturb slugs: Try to point out slugs in their original location. You can show how conspicuous or well camouflaged they are. If you took them away, put slugs back exactly where you found them. Many only eat a particular kind of food. Their mother would have laid her eggs on the food. If removed, they may not be able to find their food and may die.

Don't encourage people to handle slugs Many slugs are delicate. They may drop off parts of their body when they are stressed. Don't pinch the edges of slugs or pick them up by their edges. The slug may break off that part of their body.

Some slugs may also release unpleasant chemicals that can cause irritation to the skin or eye.

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