In this episode of RTÉjr Radio's Let's Dive In, Julie and Phil join forces with Collie Ennis to find out how snails grow their shells.
Collie Ennis, Zoologist extraordinaire and Critter Shed podcast co-host has joined forces with us once again in the name of science!
Whilst out on a wet and windy walk, 2-year-old Selena asked me: How does a snail grow its shell? Is it born with a shell?
Julie explains it all here...
Let's start with the second part of the question: Is a snail born with a shell? The answer, says Collie, is yes! Most snails hatch out from eggs, and at this point their shells are very soft and under-developed, says Collie. "So the first thing they need to do is get some calcium into them." And where do they get the calcium from? "From the egg they just hatched out of. So they’ll actually start eating their egg." That calcium then goes straight to the shell, which hardens and starts to grow.
Once that egg has been munched up though, the snail has to slither away and find some other sources of calcium. For us, traditionally, we go for a cup of milk. But snails would struggle with the straw… so instead they eat…well…most things. It will absorb minerals and calcium from whatever it eats, even from rocks on the ground.
All this yummy goodness then gets mixed up with proteins and other biological juices that the snail has. Then the snail uses a special organ called the Mantle to help it make the shell. A snail’s mantle is not a cloak; it’s an organ that is connected to the stomach and that sits right underneath the shell. "It’s like a biomineral factory that produces this kind of living rock," says Collie. "They literally are biological rocks. And the mantle is the foundation of that."
Now, have you ever taken a good look at a snail shell? I know we all can see the swirl of the shell, but have you ever seen the bands? Some are thick, some are thin, and some are different colours. The thicker bands show a period when the snail has been eating lots and making lots of new shell. The thinner bands are when the snails are inactive - hibernating or estivating.
"During winter months in Ireland and in Europe, the snails will hibernate and the shell won’t grow as much. In hotter countries, snails will estivate, which means that they’ll go and bury themselves in the ground, during the hotter months," says Collie. And during those months the snails will shut down and the growth won’t happen. So, "that’s how you can tell how old a snail is: by counting the rings on its shell!"
So really, snails are like trees! Go on, go and have a look in your garden for a snail and see if you can tell how old it is by counting its bands. As a guide, a general rule for most snails is that each ring or band counts for one season: a large ring of growth for summer/wet season, and a small one for winter/dry season.
Now if you were to keep a snail as a pet, as Collie did when he was a wee young lad (and still does!), then you can get a close-up view of the snail growing. If you look closely where the snail's head comes out of the shell, "you can see the soft edge of the snail…the soft edge is where the new shell is being formed. That pushes back and goes into the spiral."
So, if you’d like a new pet for Christmas or your birthday, why not save your parents the expense and get a snail, instead of a hamster? I guarantee the snails won’t bite or run away from you so fast you can’t tell where its gone. But if you don’t want a snail in your house on a long-term basis (i hear you, parents), then maybe just look after one and observe it for a few days.
What you’ll need:
- A snail, from the garden
- A plastic container with a lid
- Some soil
- Some "furniture" for the snails' new home: a small plant pot or something that could make a dark hidey-place for the snail, a stick for it to climb maybe?
- A plate of some form for its food
- Left over veggies from the fridge
- Something sharp to make airholes in the container lid, and an adult to help you make the holes.
- A spray bottle
What you need to do:
- Create a home for your snail
- Put the soil into the container and put the "furniture" listed above on top!
- Ask an adult to help you put some small holes in the lid of your snail home
- Find a snail in your garden
- Pop the snail into its new home
- Put a few bits of cucumber or carrot down on the plate or dish for it to eat
- Add a bit of water with a spray bottle to keep the snails moist
- And observe!
Collie’s favourite snails are African Land Snails. These, dear reader, can grow up to the size of a rugby ball. A RUGBY BALL SIZED SNAIL. Can you imagine it? I can’t.
These snails are originally from places in east Africa, but they’ve been brought all around the world. But as you may have learned in your biology lesson already, animals evolve to become adapted to their habitat, and the African Land Snail is no different. Their main special adaptation: they’re big, they’re chunky and they have very thick shells. And the reasons for this are twofold, says Collie.
The first, is personal safety. "There’s a lot of predators going around that specialise in eating snails, from birds to reptiles, so they have to have this thick, almost concrete-like, rock solid shell."
Secondly, you’ve got to stay hydrated when it’s hot. "The snails that have evolved [in Africa] have thicker shells that can retain the moisture a lot longer, and survive a lot better."
So there you have it, snails are awesome. They are basically a slimy foot that creates its own biological rock for a home!
And please send us photos of your snail homes - we’d love to see them! Please also subscribe to the show to make sure you don’t miss any of our episodes from this season, or our other two seasons.
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