No. 09–More on Whelks

In the last issue you were introduced to the four species of whelk that inhabit local waters. From largest to smallest they are the Lightning, Knobbed, Channeled and Pear whelks. You were also told of the Florida Horse Conch which is neither a conch or a whelk but does grow to be the largest of local snails.

Neither whelks or the horse conch are above scavenging a meal if the misfortune of another presents the opportunity. They are, however, quite efficient predators feeding primarily on bivalves. Our young resident knobbed whelk of about five inches in length has consumed eighteen clams of between two and four inches, a couple dozen medium to large mussels and a number of oysters since the Estuarium opened in October, ’02.

You may wonder how a snail without a shucking knife would take on the task of opening an unsteamed clam. The answer is a combination of brute force and precision. The whelk will wrap its muscular foot around the clam and thus grasping it, will twist its body bringing the opening edge of the clam into parallel alignment with the outer edge of its own shell. By feel, the whelk gauges the seam between the two halves of the clam shell and begins to apply pressure. If not properly aligned, the whelk’s pry will result in its shell slipping off the to the side and the alignment process will begin again. Even initially unsuccessful attempts are not always a waste of energy. Often a small piece of the clam’s shell will be chipped allowing the whelk to attack a compromised point of defense on its next try.

The relative sizes of the clam and whelk factor into how long the struggle will go on but almost without exception, the whelk will ultimately prevail. Once the whelk has breached the clam’s defense, it’s all over but the eating. Ok, so a snail can open a clam without a shucking knife, so now what? So now for the really interesting part…

With the hapless clam’s shell pried open, from the center of the underside of the whelks head area through a slit in its skin there emerges a proboscis. It looks like a fat purplish worm which may be up to six inches long and it has a mouth with shredding radular teeth at the end. Poor clam. It doesn’t take much imagination to figure out what transpires once the proboscis goes into action.

The ribbed mussels of the area don’t pose much of a challenge for the whelk as far as breaking them open goes. Their shells are much less dense and break with relatively little effort in the whelk’s embrace. Accessibility is more the issue as mussels tend to burrow leaving little of their surface exposed or bind themselves tightly within the nooks and crannies of hard objects.

We will continue on the topic of whelks with the next issue.