Grainworm means: a kind of Nereis worm, also known as wart-nosed Nereis worm. In autumn, they migrate upstream from the sea to estuaries or to offshore rice fields to reproduce.

The wart-nosed nereid is a polychaete animal that is distributed in the estuary areas of the Yellow Sea, the East China Sea and the South China Sea. In Fujian and Guangdong provinces, as well as Shanghai and Nanjing, fishermen often catch and sell their sexually mature nereis in large quantities. The body is used for human consumption or as fishing bait. Because the body is full of gonads, the body of the worm is also a favorite bait for fish. When Nereis verrucosa inhabits rice fields in estuaries, it often eats rice roots and causes losses to rice farmers. It is an agricultural pest and was recorded as a grass insect in ancient China.

The wart-nosed nereid is a polychaete animal that is distributed in the estuary areas of the Yellow Sea, the East China Sea and the South China Sea. In Fujian and Guangdong provinces, as well as Shanghai and Nanjing, fishermen often catch and sell their sexually mature nereis in large quantities. The body is used for human consumption or as fishing bait. Because the body is full of gonads, the body of the worm is also a favorite bait for fish. When Nereis verrucosa inhabits rice fields in estuaries, it often eats rice roots and causes losses to rice farmers. It is an agricultural pest and was recorded as a grass insect in ancient China.

Morphological characteristics of the grass insect:

The body of Nereis verrucosa is slender and slightly flat, 40 to 80 mm long, about 5 mm wide, and has more than 60 body segments. The color from the back of the front end to the base of the mouth is greenish-brown, the back is slightly reddish, and the center of the back is light red. The head is slightly hexagonal and has 2 pairs of large eyes. There is a mouth in the center of the ventral surface of the head, 4 pairs of tentacles, and 2 tentacles and tentacles each.

The snout is divided into two parts, the front and back, and each part is divided into 3 small areas. The snout has no small teeth, but soft protrusions; the small protrusions are not obvious in areas Ⅰ and Ⅱ, and there are about 20 small columnar protrusions in areas Ⅲ and Ⅳ. , there are 4 large protrusions in areas V and VI. Dark green, with 1 to 2 small protrusions on both sides, and a row of large protrusions on the front edge of areas VII and VIII.

There are warts on both sides of the body segments, and there are a few setae starting from the 4th pair. The warty legs in the middle part of the body have large basal leaves on the dorsal barbels, the same length as the ventral barbels, the basal leaves are not obvious, and the dorsal limbs are smaller. There is a tongue-like leaf on the ventral side, with many and long setae, most of which are paddle-shaped. There is a pair of small anal barbels at the anal segment.