Moths are known to engage in acoustic forms of communication, most often as courtship, attracting mates using sound or vibration. Like most other insects, moths pick up these sounds using tympanic membranes in their abdomens. An example is that of the polka-dot wasp moth ("Syntomeida epilais"), which produces sounds with a frequency above that normally detectable by humans (about 20 kHz). These sounds also function as tactile communication, or communication through touch, as they stridulate, or vibrate a substrate like leaves and stems.