by B. N. Sullivan
Tiger Cowries (Cypraea tigris) have several claims to fame in Hawaii. Two of those claims have to do with their size. The third claim to fame has to do with a traditional use for the shell. (More on that in a bit.)
Tiger Cowries live on tropical reefs in a wide range of places throughout the Indo-Pacific region. They can be found as far west as the Red Sea and the Indian Ocean, and as far south as the tropical shores of Australia. They live as well along the coasts and islands of southeast Asia, and in many locations in the tropical western Pacific. Hawaii is the northeastern-most place on the globe where Tiger Cowries are found.
Tiger Cowries are the largest of the many species of cowries found in Hawaii. Not only that, those in Hawaii grow larger than Tiger Cowries found anywhere else in the world. In Hawaii, Tiger Cowries can grow to nearly 15 cm (about 6 in). Elsewhere, they rarely grow bigger than 10 cm (about 4 in).
Hawaiian Tiger Cowries occur in reef areas at depths from about 4 m to 40 m (about 10 ft to 130 ft). This depth range is another thing that sets them apart from Tiger Cowries found elsewhere. Outside of Hawaii, the species usually is found only in shallow waters, including the inter-tidal zone.
Snorkelers and divers sometimes get to see these shells during the day. Tiger Cowrie shells are very beautiful: they are white or creamy ivory, and covered with irregular dark spots. The spots are mostly brown, but some individuals have a mixture of brown and bluish gray spots. The elaborate pattern of spots on each shell is unique.
The snails usually stay tucked up inside their shells during the day and forage at night, so you have to find one after dark to see evidence of the gray snail that lives inside. At night the animal emerges and crawls along the reef, carrying its shell on its back.
The first photo on this page is a head-on shot of a Tiger Cowrie snail poking out of its shell. If you look closely, you can make out the snail's proboscis and tentacles. It uses these organs to 'sniff' for food and gather it into to its mouth. Tiger Cowrie snails are herbivores -- that is, they eat seaweed and algae.
As the snail moves along to graze at night, it extends its mantle up over the shell. The mantle, with its prickly looking papillae, acts like camouflage when it covers the shell. The snail secretes a mucus that not only facilitates sliding the mantle over the shell, it also keeps the surface of the shell polished and shiny, looking like glazed china or porcelain.
In the second photo on this page, the snail is just beginning to slide its mantle up the side of the shell. In the third photo, the mantle has extended almost completely.
Now, about that third claim to fame. Tiger Cowrie snails are a favorite food of octopus. This was a fact well-known to traditional Hawaiian fishermen, who made lures from Tiger Cowrie shells to attract 'tako' (as octopus is called here in the islands).
Some Hawaii fishermen still use these lures to fish for tako. Writer Jim Rizzuto, well-known in Hawaii for his books and newspaper columns about fishing, discusses these lures and explains how they are made in his book Fishing Hawaii Style, Volume 2 (Honolulu: Hawaii Fishing News, 1987). He notes that the local Tiger Cowrie shell "is easy for the tako to see and is irresistible."
If you would like to try your hand at making a traditional tako lure from a Tiger Cowrie shell, here is a a link to a document from the University of Hawaii at Hilo that tells how to do it: Create a Hawaiian Tako Lure (11-page 'pdf' file).
About the photos: All of the photos on this page are of the same individual. I took these photos during a night dive at Paniau, at the southern end of Puako reef, which is on the western coast of Hawaii's Big Island. Click on any of the photos for a larger view.