Hīhīwai (Neritina granosa) are freshwater snails endemic to Hawaii. They can grow up to 3 centimeters (1 1/5 inches) in diameter and have a dark shell with a few red spots. The shell has gnarled protrusions and both a rough and a smooth surface. The operculum—a structure attached to the surface of the snail’s fleshy foot, protecting the inner part—is orange. The snails feed on algae growing on rocks.
Hīhīwai are similar to limpets, and tend to hide under rocks and in crevices during the day, coming out at night to feed and mate. These snails require clear, cool, well-oxygenated streams with rocky bottoms, and are most abundant in fast-flowing water. Their strong, muscular feet allow them to climb waterfalls and attach themselves firmly to rocks.
Hīhīwai deposit their eggs in small whitish-brown sacs, which they attach to rocks or in the shells of other organisms. Each sac contains about 250 eggs. When the eggs hatch, the larvae are drawn into the ocean where they will spend a year as ocean plankton. The post-larvae, called spat, will move upstream in a line during the summer months, migrating until they find a suitable place to spend their adult life. From then on, most adult hīhīwai do not move more than 20 meters (65 feet).
The hīhīwai is also called wī, which also means "famine" in Hawaiian. This name suggests their important role as a source of food for the islanders during past times of food scarcity. The custom was not to say that one was leaving to collect wīs, to avoid finding only empty shells; it was thought that the spirits of the night would hear, and take the wīs before the harvest. The Hawaiians also referred to this species as hapa-wai (half water).
They are eaten raw, after salting the extracted meat. In the past, they were cooked in bundles of leaves or in gourds by placing them next to hot stones; the flesh was then more easily removed from the shell.
The life cycle of the hīhīwai illustrates the strong "mauka to makai" (mountain to ocean) connection necessary for their survival. In fact, hīhīwai need an uninterrupted link between the stream and the ocean, the two environments in which their life cycle takes place. Water diversions and dams can pose a threat. In addition, habitat degradation and pollution can lead to poor-quality water in which the hīhīwai cannot survive.
Hīhīwai were more abundant in the past, particularly at the mouth of Waikolu Creek. Snail populations were severely depleted by a large landslide in Pelekunu Creek in 1986 that destroyed the habitat. Hīhīwai are also preyed upon by invasive species, particularly crayfish (Macrobrachium lar).