• Question: We saw a squashed slug once and wondered what it's insides were made of.

    Asked by anon-258474 on 10 Jul 2020.
    • Photo: Martin Coath

      Martin Coath answered on 10 Jul 2020:

      Mostly water, but the insides of a slug also have cells making up a digestive tract, the reproductive organs, something akin to a ‘brain’ and nervous system (both very simple), muscles and so on. All the normal stuff really! 🙂

    • Photo: Evelyn Greeves

      Evelyn Greeves answered on 10 Jul 2020: last edited 10 Jul 2020 3:31 pm

      I imagine it’s insides are made of very similar things to the insides of you and I!

      Although the exact arrangement will vary, a slug needs just the same things to survive as us. We both have lungs, so we can breathe in oxygen. We both have blood, to carry the oxygen around our body, and a heart to pump the blood around. We both have a stomach so we can digest the food we eat to get energy, and we both have an anus to get rid of the food we can’t digest! We both have eyes, and a brain, to process the world around us. We even both have a liver and kidney(s) to filter nasty things out of our blood.

      Obviously the inside of a slug looks very different to the inside of a human. But at its core, it is almost the same. This is because at one point in history, we had a shared ancestor who probably had all the things I just described. In fact, all of the animals in the world can be traced back to a single shared ancestor. Which is pretty cool, I think!

    • Photo: Imogen Cavadino

      Imogen Cavadino answered on 17 Jul 2020:

      The body of slugs and snails are really unusual, in that they are completely asymmetrical! Most slugs and snails have their main body openings on the “right hand side” of their body (it’s easier to say that, even though slugs don’t have hands). This includes their breathing pore, which you can see opening and closing when slugs crawl along.

      The lungs, heart, kidneys and most of the body organs are held in the fleshy saddle shaped flap of skin at the front and top of the slug, known as the mantle. Most of the body organs you would see on a squashed slug will be from the main body cavity. The vast majority of this contains digestive organs, and in mature slugs a lot of genitalia as well. Slugs are both male and female at the same time, so have some very complicated genitals.

      Towards the front of the body, you have the sensory tentacles, the top set which contain the eyes. Slug eyesight isn’t good at all; they can only see shades of light and dark. They also have a simple, circular “brain”, which is made of nerves. Strangely, in most British slug species the brain is actually a doughnut shape, with the throat passing through the middle!

      Most of a slug is made up of soft tissues, they don’t have a skeleton like us. Some slugs have the remains of a shell hidden inside the skin of the mantle, left over from when they evolved from snails thousands or millions of years ago. These shells are mainly made of calcium carbonate. The only hard parts, other then the shell, are a tongue like structure in the mouth containing thousands of tiny teeth (the radula), and a few tiny jaw “bones” which are made from a substance called Chitin. You can see some photos of these teeth and mouth here: https://nhm.org/stories/microscopic-look-snail-jaws

      The blood of slug is also different to ours. Human blood is iron based, making it look red, while slug blood is copper based, which makes their blood a greenish colour! Another vital part of a slug is slime. This gives them protection and allows them to move around. Their slime is made up mostly of water and proteins. The biggest threat to a slug is drying out!

Comments