02 October 2008

Sidewalk snails

Yesterday and today I witnessed a peculiar phenomenon near my office building in College Park, Maryland: live and dead (crushed) land snails on sidewalks. What makes this unusual is that these are the sidewalks that I have been walking on for about 3.5 years, but I had never seen snails on them before. If I had seen one or two snails, I wouldn't have thought it significant, but today at one location, over approximately 20 m I found 16 live and several crushed snails. Luckily, that particular sidewalk doesn't get much foot traffic; otherwise the casualties would have been much higher.

Here are some of the snails.


There were 3 species: Mesodon thyroidus, Ventridens ligera and an unidentified Triodopsis.

This is what the location looks like.


I am assuming the snails came out of the grassy area or the wooded lot behind it. But why were they on the sidewalk? Besides,. The snails are probably coming out at night, although the night time temperatures have been low lately, and then getting stranded on the sidewalks after the sun comes out.

The other 2 locations where I also found snails on the sidewalks are within about 200 m of the above location and more or less similar in habitat characteristics: a sidewalk separated by a wide grassy strip from forested areas. We hadn't had rain for about 2 weeks, but the past 2 days have been rainy. It is possible that when the rains came, the snails suddenly became active, but that wasn't the 1st time we had experienced a dry period followed by rain. If this was something the snails often did, I think I would have noticed it before. Did all 3 species experience a population explosion over the summer?

Here is a newly adult Mesodon thyroidus that I found in the middle of the sidewalk at one of the other locations. Moments later a couple of men, one of whom was pulling a bag on rollers passed over the spot where the snail had been. I had come to its rescue right on time.


I moved all the live snails I could find to the tall grass.


Bruce Berman said...

I had a similar experiencein Boston (actually Brookline) Massachusetts this summer after a big rainstorm.

I saw several dozen garden snails and grove snails on the sidewalk where I have walked regularly for the nearly 10 years I have been at BU.

It seemed to me that the sudden andheavy rains had washed them towards the street and the stormdrain, though by the tine I saw them they were pretty dispersed on the sidewalk:

I love your blog, and encourage all my students (particularly the many visiting turkish students I teach each year!) to read it.



Katie said...

Some of the nature preserves I have visited I have noticed stranded snails on the boardwalks. I too, have picked them up and put them into the vegetation areas.

David said...

How does one know that the Mesodon is newly adult rather than an old adult? The freshness of the shell?

M. thyroidus regularly come out onto the paved walk through some woods near my house, but only after rain. They appear to be grazing on algae(?) that slick the surface of the walk.


Bruce: Glad to hear you like my blog.

David: It's not obvious in the above picture, but the lip, although reflected, was rather thin.