Sunday, April 20, 2008

And would you call it a swarm of snails?

Out for a quick walk, we passed three large trees in front of a townhouse complex. They will be covered in pink or white blooms soon, but for now, they're just barren branches. We were surprised to see several snails climbing the first one; there's nothing to eat up there yet.

The next tree had more. Quite a few more; one every foot or so, bottom to top, all around the trunk. A snail traffic jam.

They came in a sampler of colours and patterns; yellow, brown, single-, triple- or un-striped, smooth, ridged. We went wild, taking photos of all within reach. Here are the main types:

1. Greenish-yellow, one narrow black stripe per loop.

2. Highly ridged brown, very faintly striped.

3. Pale, almost transparent brown, darkening towards the centre. Smooth. No striping.

4. Another smooth brown one, very faintly striped.

5. Brown, black and reddish stripes, three per loop, on a yellow base. All of these were highly pitted, as if they had attracted attention by birds too small to break through.

These couldn't be all the same species. Could they? But if not, why were they swarming? I spent the evening tonight reading descriptions of local snails and looking at photos.

I found a Guide to the Snails of the TWU Campus, which is just a few miles east of here. From there, I selected a few possibles: Monadenia fidelis, for the striped snails, Haplotrema vancouverense for the pale brown one, Cryptomastix germana for the ridged brown one. But when I Googled these separately, I ran into problems. None of these quite matched up; most Monadenia photos had no stripes, and they were reddish rather than yellow. Cryptomastix was a dwarf species. Haplotrema always had a pale cream body; I already had a photo of the pale brown snail and its body was blackish.

Back to the drawing board. I Googled all the snails on the TWU site. Aha! Cepaea nemoralis, the grove snail, fitted, even though the TWU photo didn't. Biopix gave me a whole page of photos, and cleared up most of the mystery.

Cepaea is an extremely variable species. Wikipedia says,
Apart from the band at the lip of the shell, grove snails are highly polymorphic in their shell colour and banding. They range from almost white, through yellow and pink to dark brown, with a range of light and dark bandings. The bandings vary both in colour and number (but never more than five bands).
One problem remained. The Royal BC Museum write-up describes the body:
The body of this snail is cream coloured/pale brown, becoming darker towards the head and on the tentacles.
None of the snails on the trees was going anywhere; not a body, not even a tentacle was visible. But I had photographed a couple of these snails before, nicely extended.

See the problem? Dark brown body on one, blue-black on the other. Not cream coloured. Not even close.

More Googling. (What did we ever do without Google?) Photo # 13 on the BioPix page is of a Cepaea (They call it the Brown-Lipped Snail rather than grove snail, but a few colour morphs have a white lip. Naturally.) with a brown shell, but a black body. Problem solved.

From now on, it will be hard to convince me that any snail I see, no matter what colour, pattern, or size, is anything but Cepaea. They're all grove snails. The whole kit and caboodle.

Two more questions remain. There were snails on the first tree, many on the second. And on the third in the row, the same type of tree, not a single snail. Why?

And, in Photo # 1, above, what is that pile of stuff beside the shell? Snail poop?


  1. Dunno why they favour particular trees. The same thing happens here with the introduced white snail (Theba pisana). They are particularly fond of road markers --- but only certain ones. Have no idea what the criterion is for a good marker.

    And yep. It's poop. Sometimes garden snails (Cantareus aspersus) gather it up and tuck it under their foot.

  2. Snail,
    That was fast! Thank you.

    "... fond of road markers ..." with "a better view." :D


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