Butterflies are a rather quiet group as a whole, communicating visually and chemically, rather than acoustically, so they generally don’t have much use for ears. That said, there are exceptions.
Satyrids – the group that includes browns and ringlets – have an eardrum at the base of each forewing, which is connected to a swollen vein along the wing’s leading edge. The vein gathers soundwaves and funnels them onto the eardrum.
Their function, it seems, is to detect approaching predators, especially birds. The ears are particularly sensitive to low-pitched sounds, such as the flapping of feathered wings.
Why do moths have ears and butterflies don't?
It’s probably no coincidence that butterflies tend to fly by day, when sight is more useful, whereas nocturnal moths rely more on sound and smell. It was long thought that moth ears evolved to detect the approach of echolocating bats so that the insects could take evasive action.
But the recent discovery that moths evolved ears before bats even existed has put paid to that one. It’s likely that they did evolve to detect nocturnal predators of one kind or another, though. They are often located on the body, close to the wings – a good place to have them if their primary purpose was to elicit a quick escape response.
Main image of butterfly © Getty