Sea Shell Holes
Date: August 2007
My family and I collected some seashells on vacation,
and when we were going through them we noticed that some of them had
a ittle hole at the top and some of them did not. What is the
reason or this? What is the little hole for?
My wife and I used to collect shells while living near the ocean. We
had exactly the same question. The holes often looked so very
deliberate and circular that we figured there had to be a reason.
It turns out that the hole has a definite purpose, but it's not for the
benefit of the creature living inside the shell. Instead it's usually
drilled there by something else looking to eat the animal inside the
shell. I think there are several species of mollusks and snails that do
this in order to feed.
Michael S. Pierce
Materials Science Division
Argonne National Laboratory
One mechanism is the rubbing of the shell against sand. Shells get rubbed
against sand as they are washed up on shore. Remember, in the wild, the
shell of a living bivalve is rough. After it dies, it's polished by the
grinding action of the sand. Due to the shell's shape, the top and bottom
get ground down first. As the bottom (open end) gets ground, it just gets
shorter. However, since the shell is hollow, when the top gets ground down,
it can make a small hole in the top. Take a whole shell and grind it down on
a flat surface -- see how a hole can form? If you look, you can also find
'rings' or 'c-shapes' of shell on the beach too. These are bits of shell
where the top and bottom have been ground down substantially. There may be
other mechanisms as well.
Hope this helps,
Click here to return to the General Topics Archives
Update: June 2012