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On slugs and snails

June 7, 2011

Slugs (no shell) and snails (have shells) may become pests in a Chiang Mai garden. The Tropical Leatherleaf (Laevicaulis alte sensu lato, tak nang) is a flat, brown slug which often hides its tentacles. It is well adapted to the dry lowlands, hiding underground at daytime, and feeding on your plants at night. At Dokmai Garden it is not a big problem because we have so many wild and domestic birds feeding on it.

Another Chiang Mai gastropod is the East African Landsnail (Achatina fulica, hoi tak african). It can grow big as a hand, and has a conical and quite ornamental striped shell. These snails eat plants and even concrete to get calcium for their shells. The snail was reported from China in 1931, where it was introduced as food. During rainy years it is very prolific and your chicken may not be able to open its very hard shell. In fact, I (80 kg) have several times stood on a big shell, without it cracking. You have to put the snail on a stone and then use force to stamp on it. Once the fortress is open you can let the chicken have a feast.

A third invasive gastropod is the Golden Apple Snail (Pomacea canaliculata, hoi cherry). It is an underwater snail, with yellowish round shells that can grow big as an apple. Its spectacular pink eggs are laid above the water level. This snail was introduced from South America to clean fish tanks, and was promoted as a food for people. It was found in the wild in Thailand in 1984, and is now the most serious pest in rice and taro fields. This has resulted in an increased use of pesticides. This seems unnecessary, as many wild fish, birds, mammals and crabs eat the snails. Since such predators are almost extinct due to cats, dogs and hunting, the snails propagate out of control. Also in natural wetlands, this snail eradicates the native flora, and outcompetes its Thai cousin Pila polita (hoi kong), which has white eggs and darker shells.

All of these gastropods may be vectors of the rat lungworm (Angiostrongylus cantonensis, pajat toa gom), a nematode that resides in lung arteries of rats, and may infect humans, causing fatal encephalitis as a result of undercooked snails or unwashed vegetables. Slugs and snails can be controlled by fowl, herons and frogs. Nocturnal snail hunters such as fireflies, which are most spectacular beetles in any garden, benefit from a heap of branches to promote breeding. Gardeners can make a difference by creating a refuge for Thai wildlife!

Text and Photo: Eric Danell

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