Light salt water or clean water. You can use light salt water or clean water to put the bean curd into the bottle. They can be put into bottles and stored in the refrigerator. Doudan is the larvae of the bean hornworm. It makes a living by eating soybean leaves and acacia tree leaves. It is a naturally non-toxic and pollution-free insect that grows in a pollution-free state. It has a graceful body shape and is similar to silkworms. It is particularly common in most areas of Shandong and northern Jiangsu. When mature, it will burrow into the ground and lie dormant until it emerges into an adult next year.