any of approximately 25 species of rare and primitive insects found in the mountains of Japan, western North America, and eastern Siberia. A pale, wingless creature 15 to 30 mm (0.6 to 1.2 inches) long, it has biting mouthparts, long antennae, and small compound eyes. Grylloblattids usually live beneath rocks near mountain snow lines or beneath rotten logs at lower altitudes. They feed on other insects.