Why Trapdoor Snails in Ponds?  All the pond books recommend these belly foots (gastropods) for ponds.   Theoretically, trapdoors make excellent algae eaters.  However, we’ve never been able to measure their effectiveness -- even when kept in mass quantities.  We know they eat it.  We don’t think they can eliminate it.  (Try mowing your grass while blindfolded.)  But we know snails in ponds (and aquaria) help remove excess foods and any undetected dead stuff they can reach.  Snails will eat stuff nothing else will touch -- like moldy old fish food.  Maybe not the best diet for them, but they help prevent the overfeeding syndrome so common with new aquarists/pond keepers.

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Appearance-wise, trapdoor snails are hard to tell from a mystery snail -- shell more pointed.

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Trapdoor snails (like most snails) slam their trapdoors when picked up or pestered.

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So do mystery snails (left) and apple snails (right).  Not a big deal.

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Note the three open siphons that inhale water into their gills.  Most trapdoors are closed.

Trapdoors versus Mysteries.  The biggest difference between these guys and mysteries and apples is their lack of a lung.  They never run up a snorkel to suck O₂ from the air.  These means they do not drown when ice covers their water -- a recurring problem in our neck of the corn belt buckle.  Better yet, since they suck no air, cool weather won’t kill them.  Mysteries and apples can’t make the cut.  

Trapdoor Mortality Clue.  Most of the larger snails grow a trapdoor and slam it shut when you bug them.  It protects their edible insides.  When that trapdoor falls off, they are dead.  Really dead.  You need not feel for a pulse.  And that smell ...  Who could scarf escargots after smelling a ripe snail?  Erasers taste better.  Even with the garlic and Frenchified “I can’t believe it’s not ear wax” sauce.

Trapdoors and Gravel Cleaners.  If you’ve ever cleaned a tank with a gravel cleaner, you hate those loose trapdoors.  They clog your gravel cleaner.  If they get inside your siphon hose they can drive you just a bit crazy.  They totally mess up the flapper-style self-starting gravel cleaners.  Some disassembly required.

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Mystery snails sport two extra "antennae" and that snorkel on the right.  Same mouth.

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Not quite as pretty as the mystery.  Still very utilitarian.  Excellent scavenger.

Great Scavengers.  Dropping two or three big snails of any kind into a new tank helps prevent cloudy water.  They eat up excess food faster than the bacteria can find it.  Their eyesight would never pass a driver’s license exam, but they sport super smellers.  

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Trapdoor snail hard at work inside a glass chimney from an oil lantern.

Plant Eaters?  Of course.  If given no choice, all snails will eat plants.  So will you.  Apple snails even eat sponge filters.  Trapdoor snails are not quite as voracious.  But put a dozen in a 10-gallon tank with no food and they’ll eat filters, too.  They much prefer fish food.  In the absence of fish food, they will eat algae AND plants.

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Or put a 100 in a 55 with goldfish and they even eat the algae off their buddys' shells.

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At "come as you are" events, trapdoor snails arrive wearing a coat of algae.

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Out of all those adults, there was only one baby  -- on top this female (same snail).

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Later, this little lady trapdoor snail started cranking them out.

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More of her progeny.

Livebearers.  We almost forgot to say that you won’t find egg clusters underwater or egg cases above the water.  Trapdoor snail mommas have little live babies that come out ready to eat whatever they roll over.  If the adults have no other food, they will also eat escargots.

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Even out of the water, you can see the algae that grows on trapdoor snail shells.

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In the water, you see the algae crop on this trapdoor snail even better.

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Trapdoor snails clean up pretty good.  This guy's hard at work already.

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Here you can see their little speckled snouts working away.

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Little pleco giving a trapdoor a hair cut.

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When your snails come to the top, it's time to change your water.

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Here's a pile of 165 trapdoor snails.

Last Words.  We like all snails.  We consider trapdoor snails over rated as algae eaters, but we still recommend them.  They prevent many problems in overfed aquaria.  If you want to maximize your herd, separate your adults from their progeny.  LA.

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