Mustilia castanea is a small insect belonging to the order Hemiptera and the family Miridae. It is commonly known as the chestnut bug due to its reddish-brown coloration. This insect is found in various regions, particularly in deciduous forests where it feeds on the sap of chestnut trees. Mustilia castanea has a distinctive triangular shape and is known for its ability to emit a strong odor when disturbed.