Knobbed Whelk

(Busycon carica)

Overview

Knobbed whelks are a kind of marine snail whose shells are commonly found washed up on East Coast beaches. Beachgoers often confuse these whelks with conchs, another kind of marine snail; true conchs, though, are found in more tropical waters.

Knobbed whelk shells are typically grey, ivory or tan in color, often with brownish streaks, and have distinctive peaks along the spiral top. The shell is made by the snail's mantle, which secretes minerals and proteins that solidify in layers. The whelks' soft bodies are pale grey and tan with dark streaks or speckles around the edges of the foot and along the tentacles on the head.

The egg cases of knobbed whelks also routinely wash up on mid-Atlantic beaches. These egg cases resemble a coiled string with a series of narrow, leathery, quarter-sized pouches attached. Females lay these cases during warmer months, anchoring them underwater in mud or to rocks. Each pouch contains dozens of baby whelks that develop over a few months. Ideally, the egg case remains attached until the babies hatch and crawl away. Sometimes, though, they detach early and get flung ashore by the waves. If you find a dried egg case, give it a shake. If you hear it rattle, break a pouch open—you should find tiny whelk shells inside!

Quick Facts

Learn more about knobbed whelks! Did you know whelks are a kind of gastropod? Gastropods include all marine, freshwater, and terrestrial snails and slugs. The word gastropod comes from the Greek gaster, meaning "belly," and pous, meaning "foot." Pretty fitting, given the animals in question.

Knobbed whelks are found on the North Atlantic coast from Massachusetts to Florida, and along the Gulf of Mexico's shores to the Yucatan Peninsula. They move into deeper water in winter and summer to avoid storms, and enter the shallows in spring and fall when conditions are more stable.

Knobbed whelks' biology keeps them limited to the East Coast and Gulf of Mexico. Their slow speed, preference for sticking closer to coastlines, sensitivity to cold temperatures and lack of a free-swimming larval phase keep them from spreading beyond this range.

Knobbed whelks are top predators of bivalves, mainly clams and mussels. Whelks can use their muscular foot and shell to gradually pry their prey's shells apart to get at the animal inside. They can also produce a shell-softening chemical and drill through the shell using their radula, a ribbon-like structure in their mouths lined with teeth. Once they have an opening, they inject enzymes to start digesting the bivalve.

Baby knobbed whelks are miniature versions of their adult form, hatching from egg cases with shells less than a tenth of an inch long. As adults, their shells usually measure 5 to 9 inches in length, but have been known to reach 12 inches. Typically, females grow faster than males and reach larger sizes.

Proper surveys of the knobbed whelk population have not been done. They are common throughout their range, leading scientists to consider them stable. However, given their slow mobility and calcium carbonate shells, they may be affected by warming ocean temperatures and ocean acidification.

Young whelks can fall prey to many creatures, like crabs, sea stars or fish, on account of their small size. Adult knobbed whelks are preyed upon by large crabs and sea turtles.

Humans also eat whelks. They're often prepared as fritters, cooked in chowders, or added to salads.

Meet the Expert Jay Bradley

As curator of Blue Wonders: Reefs to Rainforests, Jay Bradley oversees the care of all animals in Blacktip Reef, Living Seashore, Shark Alley and more.

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