Blind As A Bat – How True Is The Saying?
Few of us will have managed to escape without hearing someone termed ‘blind as a bat’ at some point in our lives, and with the frequency of the phrase we’d be forgiven for making the natural assumption that these creatures are somewhat optically challenged. In fact, many of us probably wouldn’t turn our heads if told that bats had no eyes at all, but the facts really are much different.
Fact or myth?
There are an estimated 1,100 species of bat currently flapping their way around the night skies, and not a single one of them is sightless. Amazingly, quite the opposite is true in many cases with a lot having remarkably good vision after all.
The myth probably came about because of the erratic way in which bats seem to fly around above our heads – if you’re out at night and there’s a bat somewhere close by, you’ll probably know about it. Their flight path isn’t anywhere near as sporadic as it seems though, and rather than flying blindly through the dark, bats are actually darting around hunting insects which the human eye cannot see in lower lights.
The science behind it
Science generally divides bats into two subdivisions; the fruit bat and the insect eating microbat. Contrary to the popular belief, fruit bats actually have large eyes with a strong ability for sight – an evolution which has come about through their need to see fruit and avoid the trees it hangs from.
The microbat has quite a different method of navigation called ‘echolocating’, in which the bat emits a sound too high pitched for human ears. This sound then bounces back off of nearby objects and relays back into their ears to identify threats and obstacles in their flight path. Their significantly smaller eyes are dominated by ‘rod’ cells which are used for night-time vision, with ‘cone’ receptors which distinguish colour making up only 2-4% of their retinas.
That said, there is always an amount of light present in the dark and there is not a species of bat which doesn’t make use of this. Even the microbat uses its eyes to identify large objects and maintain a relatively even height from the ground. There is also evidence to show that bats remember distinctive landmarks and navigate using them. It is worth remembering also that although bats are nocturnal creatures it is next to impossible to fully block out daylight as they sleep – even with the thickest curtains, we would struggle to create a pitch-black room in the middle of the day.
So there we have it... there really is quite literally more to bats than meets the eye. Despite the varied value of eyesight amongst bat species, they all use it to some degree and in fact have one of the most accurate and intuitive navigational systems in the animal kingdom. Certain regiments in World War II even attempted to train bats to carry bombs into enemy camps... though it was probably best for everyone that this plan never made it to the battlefield!