The snails come from islands in the South Pacific and the zoo is a leader in the international effort to rescue them. There are several dozen related species, all grouped together in the genus Partula.
Most of them are believed to be extinct, but a dozen zoos and universities have managed to save 30 species by breeding them in captivity. London Zoo acts as a coordinator for their efforts.
Their demise began with the introduction of giant land snails to islands in French Polynesia as food in the 1960s. The land snails' population grew to pest proportions and they began to eat crops.
So it was decided to bring in Euglandia rosea, an aggressive, fast-moving carnivorous snail from the US, to keep down numbers of the giant land snails. But the predator preferred the small local Partula snails and on each island it ate them out of existence.
London Zoo has 14 species of Partula breeding in captivity and a computer database to keep track on the conservation effort around the world. The snails need the levels of temperature and humidity found in their native rainforest to flourish.
Keepers have devised an artificial diet to replace their natural food of rotting forest-floor vegetation. It is made from trout pellets, porridge oats, grass meal and a mineral and vitamin supplement usually fed to dogs.
Some of the species in London have narrowly escaped annihilation. At one stage there were just four of the Partula tohiveana species, but it has now bred to more than 1,000. A London Zoo expedition last year to the island of Raiatea is believed to have saved the last nine Partula hebe.
Experts hope that one day safe Euglandia-free zones will be established back in their native islands. 'Our main aim is to conserve them for re-introduction into the wild,' David Clarke, invertebrate senior keeper, said.
'People warm to snails in a way which they don't for insects and other invertebrates.'