Lasius fuliginosus, commonly known as the jet ant, is a species of ant belonging to the genus Lasius. These ants are small in size, measuring around 3-5 mm in length. They are typically black or dark brown in color, hence the name "fuliginosus," which means sooty or smoky. Jet ants are known for their preference for nesting in decaying wood and their ability to form large colonies with multiple queens.