A Chinese text from 304 AD, "Records of the plants and trees of the southern regions", by Hsi Han, describes mandarin oranges protected by large reddish-yellow citrus ants. The ants attack and kill insect pests of the orange trees. The citrus ant ("Oecophylla smaragdina") was rediscovered in the 20th century, and now is again used in China to protect orange groves.