apparent selection against drive-by cannibalism

[Frederick W. Schueler]

Everyone,

Along County Road 18 at our houses, there are two places where Cepaea
nemoralis snails routinely come out onto the road.

One of these is the pullover track that services the mailboxes on the
west side of the road, and the other is a patch of Daylilies around a
telephone pole on the east side.

While I have stepped on a couple snails at the mailboxes over the years,
they have always gotten back under cover before the courier delivers the
mail, and I've never seen any driven-over roadkills there.

Across the street, the Daylilies are spared because the Counties' mowing
equipment has to loop around the pole, and through the years the Daylily
patch has had a dense population of snails. Until the past couple of
years, these would crawl out onto the pavement, get crushed by passing
vehicles, and then attract cousins out to feed on their remains, until
they were crushed in their turn, eventually forming 15 cm smears of
shell & flesh.

Last year was a drought, so it may not have been surprising that we
didn't see many of these suicide smears, but with this spring & summer's
numerous storms, it's been very surprising to not see any of these
smears form, and not to have any roadkills of more than one individual.
On wet nights a dozen or more snails have been active on the shoulder at
the Daylilies, but almost none have come out onto the pavement.

Tonight the pavement & shoulders were dry. At the Daylilies no snails
had come out onto the pavement or onto the few cm of the gravel of the
shoulder visible between the pavement and the dense Hop-clovers that
have grown up on the shoulder along the Daylilies - but at the mailboxes
11 mature snails were deployed along the courier's wheel track and on
the vegetated patch between the track and the pavement.

This is a really interesting difference, and it looks like selection
against wandering into the open at the site where such wandering has
been fatal to so many, and it's very convenient to have a site right
across the street where the lack of roadkill has been so conspicuous.

fred.
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---------Frederick W. Schueler & Aleta Karstad ------------
Fragile Inheritance Natural History - https://fragileinheritance.ca/
6 St-Lawrence Street Bishops Mills, RR#2 Oxford Station, Ontario K0G 1T0
on the Smiths Falls Limestone Plain 44.87156° N 75.70095° W
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