The huge and pretty Australian land snail Hadra bipartita was the subject of a recent post at A Snail's Eye View. These snails can grow up to a rather respectable shell diameter of 68 mm.
In stark contrast, tonight I was measuring a tiny, tiny snail, Vertigo pygmaea from my backyard. At least 2 times a year, I collect all the live adults I can find, measure their shells and then return them to the yard. The sample averages are about 1.8-1.9 mm (details here and here).
Usually once a year I also mark* the shells of a number of snails. That helped me determine that adult snails can survive the winter (details here). The last time I marked some snails was on 25 December 2006 when I used red ink on 20 adult snails. To my surprise, one of the 12 adults I found today had a red mark on its shell. Prior to last December, I had used red ink also in March 2006. I will assume that an ink mark on a shell would not last that long. Therefore, the marked adult found today was probably marked last December and has been alive as an adult for at least 8 months.
Those dots in the container under the microscope are the snails I measured tonight.
*I have been using various colors of Pigma Micron pens. The ink survives on snail shells for at least 3 months. In the case of one of the snails collected today, the ink was visible after 8 months.