New Zealand insect has whale-like ears
Insect ears The iconic New Zealand cricket-like weta has ears similar to those of a whale, researchers have found.
Wetas are large nocturnal insects related to crickets and katydids. Lomas says they can be quite aggressive, biting and scratching unsuspecting humans, meaning New Zealanders have a "love hate relationship" with them.
Like other vocal insects, wetas have ears on their legs. This is to enable the small creatures to separate their ears wide enough to use their hearing as a locating device.
As part of her masters research, Lomas was trying to find out whether wetas could hear the sounds of the native New Zealand lesser short-tailed bat that walks and hunts on the ground.
She found that wetas couldn't hear the ultrasound noises made by the bats, but confirmed they had very sensitive hearing - "capable of picking up a whisper".
"The weta hearing system was completely unusual and from all accounts they really shouldn't be able to hear what they can hear," says Lomas.
Most puzzling, she says, was the fact that their ear drums were very large, thick and wrinkly, rather than taut and thin, which is what one would expect for such sensitive hearing.
"It goes against physics," says Lomas.
In her PhD studies of the Auckland tree weta (Hemideina thoracica) she thinks she might have found the secret to the weta's remarkable hearing.
Lomas developed a new technique to dissect and create a model of the insect's ear and discovered a never-before seen organ she dubbed the "olivarius" after her son, Ollie.
"The olivarius is very very delicate and the current histological techniques people were using were destroying it," she says.
Lomas found that the olivarius produced a lipid, which filled a cavity in the ear and enabled transmission of sound from the ear drum to the auditory receptors.
She also found the insects have hearing that's tuned to a range of 3 to 5 kilohertz and thinks the lipid is playing a key role in this tuning.
"We think it plays a similar role to the fluid in the cochlear in the human ear," she says.
Whales and dolphins are also known to use lipids - in a different way - to help transmit sound in the ear, says Omas.
Given the vast evolutionary gap between whales and wetas, she says the findings suggest the use of lipids in hearing evolved more than once - in a case of convergent evolution.
The low frequency band that the weta's hearing is tuned to matches the range of the rasping sounds that they make themselves, says Lomas.
"I suspect it's for communication between individual insects," she says.