Snail scourge

Look closely at a rice field or any kind of pond in Taiwan, and you're likely to see pink bubbles like these. Each cluster is about as long as your little finger and usually 5-10cm above the water line.

They're snail eggs. The gastropods are known in English as golden apple snails, and in Chinese as fu-shou-luo
(福壽螺). They're not native to Taiwan and they're considered a major pest, but they're quite interesting to look at. Unlike its dry-land counterparts, each golden apple snail has a tubular siphon on its left side. This functions as a snorkel, allowing it to breathe while submerged, and thus making it less vulnerable to birds.
According to the website of the United Nations’ Food & Agriculture Organization: 'The golden apple snail was introduced from Florida and Latin America to Taiwan and the Philippines in the early 1980s by private snail farmers hoping to reap big profits exporting snails to Europe. Easy to rear and fast breeding, the snail’s high protein content also apparently made it an ideal [foodstuff] ... Unfortunately, the snails were not a success with consumers, and ... their market value soon plummeted'.

Snails were discarded or simply escaped. They spread quickly through waterways and irrigation channels, and now a great many rice fields are infested. At night and around dawn, they feed on young rice plants. Unfortunately for rice farmers, the snails reproduce very fast. Healthy females lay egg masses of up to 500 eggs every seven to days. Pale pink egg masses are newly laid; those that are crimson are close to hatching.

Different methods of snail control and eradication have been tried. In Taiwan, fields have been treated with tea seed cake powder (which seems to kill the snails without harming the humans who later eat the rice). Raising catfish or ducks (both species eat snails) also helps.
Some farmers resort to catching the snails by hand and smashing them on the nearest road surface. I’ve seen piles of discarded snail shells near my home, and also beside water chestnut ponds a little further north.