The birds are domesticated and kept in pig and cow farms so as to eat up flies and other insects.

Ho Van Truong, a resident of Cho Gao District, said his 3ha farm, where he has five cows, 70 pigs, and some goats, chickens, and ducks, are almost free of insects, thanks to his three white storks that eat even lice and fleas.

"Storks have large appetites and digest their food quickly.

"They help clean up the environment and increase productivity as cattle and poultry do not lose blood or contract diseases."

The farmers fasten the stork by tying one of its legs to a small stone, and place a bowl of water beside it to drink. Rotten fish is used as a bait to attract flies to the vicinity of the stork.

A few days later the stork is set free after a joint on its wing is removed to prevent it from flying away. It then patrols the farm, gobbling up any insect with the misfortune to catch its eye.