05 June 2009

A snail often on trees: Mesodon thyroidus


One of the seldom discussed characteristics of the common northeast American land snail Mesodon thyroidus is that it can often be seen on trees. Baker noted in his 1939 Fieldbook of Illinois Land Snails that "On humid days, the snails [Mesodon thyroidus] may often be seen crawling over the ground, over logs or even on standing trees several feet from the ground." So it is a known phenomenon*. But, as far as I know, there are no published studies specifically about it, looking at, for example, what the snails do on trees (they are probably eating something), how long they stay on them and how high they really go.

This snail was in the park near my house last weekend. After I photographed it, I removed it and looked into its aperture to ascertain that it was indeed Mesodon thyroidus, but not the superficially similar Neohelix albolabris**.


Yes, this one was indeed a Mesodon thyroidus. Notice how much its apex was worn; there was literally a hole thru it. Such damage is often inflicted by other snails trying to satisfy their calcium carbonate requirement in areas where there are no limestone rocks.

*Pilsbry, however, didn't mention the species' tree climbing habit in his Land Mollusca of North America.
**Mesodon thyroidus, usually the smaller of the two, often has a parietal tooth, which Neohelix albolabris often lacks.

1 comment:

Anonymous said...

I have one of those. I found it at a pool, though.