 More than 20,000 species are distributed worldwide.The insects in the order have incomplete metamorphosis, and produce sound (known as a "stridulation") by rubbing their wings against each other or their legs, the wings or legs containing rows of corrugated bumps.The tympanum or ear is located in the front tibia in crickets, mole crickets, and katydids, and on the first abdominal segment in the grasshoppers and locusts.