Creature Feature: A Lightning Whelk Knows What to Do With a Clam
If you've done some beachcombing along the Gulf Coast or southern Atlantic Coast of the United States, especially after a storm, chances are that you've picked up, admired, and perhaps taken home some lightning whelk shells. They make for an interesting find. The beauty of the shells aside, their left-handed (sinistral) whorl sets them apart from the right-handed (dextral) whorl of most other univalves. The lightning whelk is, as it were, a southpaw. It's a very intriguing southpaw, too.
The lightning whelk (Busycon contrarium) is a marine gastropod mollusk, which basically means that it is a sea-dwelling snail. In the United States, all members of the diversified Busycon genus of the Melongidae family (part of the Buccinidae superfamily) are commonly known as whelks or Busycon whelks.
This particular species acquired the name "lightning whelk" because the white shells of the juveniles have chestnut brown stripes with a zig-zag pattern reminiscent of lightning bolts. Mature lightning whelks can vary greatly in color, but the shells are characteristically grayish-white, tan, or creamy yellow with an opening that can vary from white or pale yellow to orange or even bright red. Shell collectors find these variations endlessly fascinating.
Lightning whelks are widely distributed in the United States. Generally, they are plentiful along the Gulf Coast and along the Atlantic Coast as far north as New Jersey (though uncommon north of South Carolina). They inhabit national park waters in such disparate locations as Assateague Island National Seashore, Cape Hatteras National Seashore, Cape Lookout National Seashore, Cumberland Island National Seashore, Canaveral National Seashore, Biscayne National Park, Everglades National Park, Big Cypress National Preserve, Gulf Islands National Seashore, and Padre Island National Seashore.
Water temperature is a critical control for lightning whelk distribution. The sweet spot is the 77-82 degrees Fahrenheit range. When the water temperature drops below about 68 degrees, activity rates plummet and growth ceases.
Lightning whelks grow to a length of 10-15 inches and are sometimes mistaken for conchs. They live in shallow water and prefer embayments having sandy or muddy bottoms. Prime habitat includes estuaries, creeks and oyster bars. That's where this carnivorous species finds its food, which includes some scavenged carrion, but consists mostly of marine bivalves. Busycon contrarium especially likes clams.
An adult lightning whelk eats about one clam a month, and it's not very picky about the type. In areas where whelks are plentiful and take a significant toll on edible clams, shellfishermen consider them a nuisance. Whelks themselves are edible, but even though they are a popular food in some areas of northern Europe, few Americans eat them.
This is not to say that the Busycon contrarium has no fans. Collectors and casual beachcombers admire the lovely shell and its unusual sinistral whorl.
Whether you like lightning whelks or not, you have to admit that they are highly skilled clam killers. To detect prey, the whelk turns its long inhalant siphon in the direction of the current . Near the base of the siphon is a combination taste/smell organ (osphradium) that can locate food at a considerable distance by detecting its chemical properties. The process is analogous to a wolf turning his nose into the wind and sniffing for prey that's out of sight.
After a whelk detects a clam, moves to it, and makes contact, the clam hasn't got a chance. The whelk, which is marvelously equipped to get the job done, uses a technique that is simple but brutally efficient. Employing its large, muscular foot (see photo) to pry open the clam's shell, it then uses the flaring lip of its own shell to wedge the clam shell open while it inserts its radula and proboscis to loosen and remove the soft tissue inside.
The next time you find an empty lightning whelk shell on the beach and admire its beautiful sculpture, you might want to give a thought to the ingenious way this creature gets its food. Whatever else it may be, the lightning whelk sure is hell on clams.
If you know what to look for while beachcombing, you can also find lightning whelk egg capsules. In late spring or early summer, female whelks lay egg capsules in strings attached to the sandy bottom. Each little disk-shaped capsule in the string contains numerous baby whelks (protoconchs). If all goes as intended, the capsules later break loose from the string. However, many egg capsule strings break loose, wash ashore, and dry out. These desiccated strings, which are sometimes called "mermaid's necklaces," are brittle and feel like hard plastic. You can see one at this site.
Postscript: How heavily the Deepwater Horizon oil spill will impact lightning whelks along the Gulf Coast remains to be seen, but the outlook appears to be bleak in areas that are oiled in amounts sufficient to seriously disrupt the food chain on which the whelks depend.