Whelk

Specific Name: Various species, including Nassariidae lookalikes and true whelks in Buccinidae
Diet: Carnivore – scavenger or predator; eats meaty detritus, other snails, or even small inverts
Pest or Good Guy: ⚠️ Depends on species – many are pests
Size: 1–5 cm, depending on species
Breed in Captivity: Rarely – but may survive and cause issues long-term
Cautions: Easily mistaken for beneficial Nassarius snails; some will actively hunt other snails or burrow to ambush prey

Description:

Whelks are a broad group of carnivorous snails, and many of them sneak into reef tanks as hitchhikers, often hiding in live rock or sand. Some look eerily similar to Nassarius snails but with subtle differences—like longer siphons, more aggressive behavior, or a bulkier, ridged shell. While a few species may behave as harmless scavengers, many are active predators, capable of killing snails, small inverts, or even weakened clams. Their secretive nature makes them hard to identify, and they often go unnoticed until the clean-up crew starts to vanish. If you’re unsure about a new snail that behaves “off,” especially if it’s lurking under the sand all day and not interested in algae—get an ID, fast.