Then & now: Pest practice

Generations of enthusiastic Hong Kong gardeners have helped create - with the best of intentions - ideal conditions for imported pests and diseases to thrive in. Lax phyto-sanitary regulations and an open border with the mainland have greatly encouraged the introduction of exotic species. Some have become noxious pests, others simply merge with the local landscape and are eventually assumed to be of local origin - insofar as most people give them any thought at all. The giant African snail is a typical example.

During the summer, local gardeners launch early morning and late evening search-and-destroy missions in pursuit of what is itself probably the most destructive imported pest to have reached south China in many decades. First noticed in large quantities in the summer of 1945, shortly after the Japanese occupation ended, opinions differ about this horrid creature's arrival. Pre-war gardeners remember seeing (and squashing) giant African snails in the late 1930s; others swear they came from Africa via insufficiently cleaned cargo holds on wartime Japanese vessels. Others yet maintain the snail turned up from Taiwan in this period - which is more plausible given Japanese ships had no access to African ports during the war and the snail is a pest in Taiwan as well.

Whether the Japanese are to blame or not, by the late 40s the snail's loathsome presence had reached epidemic proportions. By the mid-50s it had colonised large areas of Hong Kong and was devastating local agriculture, with whole fields of leaf vegetables being reduced to slime overnight. Unlike other snail varieties, African specimens are not edible and thus have no secondary value. Otherwise, given the renowned Cantonese ability to create cuisine out of the most unpromising ingredients, African snails would have been gathered and consumed as fast as they could breed.

Hong Kong's Buddhist monasteries encouraged the snail's rapid spread. Due to prohibitions against taking life, and in the pious belief that they were helping souls on the upward path to Nirvana, the devout gathered vast quantities and then released them; further evidence - if it were needed - of the destructive unintended consequences of un-thought-out religious belief.

A far more benign introduction was that of Blake's Bauhinia ( Bauhinia blakeana), Hong Kong's floral emblem since 1965. The Camel's Foot, the original species of this naturally occurring local hybrid, came from Bengal, India, as did many of early Hong Kong's garden plants. Climatic conditions are similar in the two places and, as Calcutta was the Canton delta's major international trading partner in the late 18th and early 19th centuries, transport links facilitated migration.

The noisy flocks of lesser sulphur crested cockatoos that squawk and wheel over parts of Hong Kong Island, from Pok Fu Lam to Happy Valley, are another less troublesome imported species. Originally trapped in their thousands for the pet trade (as a result of which they are nearly extinct in eastern Indonesia), these hardy, friendly birds breed readily and escapees swiftly naturalised in Hong Kong's emergent tree cover, establishing breeding colonies. Cockies alighting on a fully-laden potted kumquat tree during Lunar New Year will reduce it to messy pulp in short order.