It is a little-known fact that the Hawaiian Islands were once home to one of the most diverse assemblages of land snails to be found anywhere on earth. More than 750 species have now been formally described and recognised by taxonomists. Sadly, two thirds of those species are now extinct and most of those that remain are threatened by a combination of habitat loss, introduced predators, and a changing climate. Amongst all these snails, some of the largest and most colourful were those of the genus Achatinella found only on the island of O’ahu.
These incredible creatures have woven their way into the rich cultural life of these islands’ first peoples, the Kānaka Maoli, and are present in a variety of songs, chants, and dances. In fact, the snails are often said to themselves sing in the forest at night as a sign that everything is pono, that is that everything is correct, righteous, and good.
[Chant by Cody Pueo Pata, “Kāhuli Aku, Kāhuli Mai”]
When fully grown, the shells of the Hawaiian Achatinella tree snails can be around two centimetres in length. One immediate question that they prompt is this: how did they, and all the other snails found in the Hawaiian Islands, get there in the first place? These are volcanic islands that have formed out in the middle of the Pacific Ocean, devoid of life. Land snails are not known for their propensity to undertake long journeys, not by land and certainly not by sea.
This is a question that has preoccupied scientists for centuries now. Over the years, countless snails, all over the world, have been submerged in sea water to see if, and for how long, they might stay alive on oceanic voyages. Other snails have been fed to migratory birds, and then the droppings of these birds have been examined for snail survivors. In yet other remarkable studies, scientists have gone looking for snails sealed up in their shells on the legs of water birds or tucked down in their feathers, and they’ve dragged nets behind aircraft flying at high altitudes to see what, or who, might be found travelling around up there. Remarkably, it seems that snails are moving around the globe in all of these ways, and probably others, too.
In the case of Hawai‘i, it would have been tiny snails, about the size of a grain of rice, that made these initial journeys. Most scientists now think that over roughly the past five million years, about 20 ancestral snails arrived in the islands in one of these ways—most likely travelling in the feathers of migratory birds. From this handful of intrepid travellers, hundreds and hundreds of new species evolved, of all colours shapes and sizes. While, sadly, most of them have now been lost to extinction, there is still time to conserve and hold onto some of those that remain, including some of the species of the genus Achatinella.