Which animals hear without ears?

Not many animals actually have external ears, so how do they hear?

Many animals have some sort of auditory organ, but outer ear like ours are rare and found only in mammals. The external structures (called auricles or pinnae) help to channel sound waves towards our inner ears, where they can be translated into electrical impulses and sent to the brain, but other species are still able to hear without them.

The oval-shaped heads of birds like crows and ducks reflect and diffract waves hitting them to allow detection of the sources of sounds. Other species, like owls, have facial discs that direct sounds towards their inner ears.

Jumping spiders can ‘hear’ people speaking several metres away despite not even having eardrums. Sensitive hairs on their forelegs vibrate when sound waves pass, causing the auditory neurons in the spiders’ brains to fire in response.

Most frogs have eardrums on the sides of their heads to directly pick up sounds in their environment, but there are exceptions. The Gardiner’s frog, a native of the Seychelles and one of the smallest frog species in the world, lacks this tympanum. Instead, they hear each other’s croaks by using their mouth cavities to transmit sound waves to their inner ears.

 

Photo: Artur Rydzewski/flickr