Orthoptera is an order of insects with paurometabolous or incomplete metamorphosis, including the grasshoppers, crickets, cave crickets, Jerusalem crickets, katydids, weta, lubber, Acrida, and locusts. Many insects in this order 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. These organisms use vibrations to locate other individuals.
Info extracted from Wikipedia