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Do Bats Really Have Poor Eyesight?

i David De Lossy/Photodisc/Getty Images

Saying someone is “blind as a bat” may once have indicated that the person had poor eyesight. However, as science discovers more about these interesting creatures of the night, we find the phrase doesn't really hold true. It's clear that bats are anything but blind. Between their amazing ability to echo-locate and visual acuity similar to that of humans, bats actually see quite well.

When Hearing is Seeing

Unlike ordinary bat vision, which depends upon external light sources passively interacting with its eyes, echo-location in bats is an active process requiring the transmission of sound by the bat and then interpretation of the echoes that bounce back from objects the sound waves hit. Bats can tell instantly by the echo whether an object is close or far away, and what shape or how large it is, among other things. When you consider bats are doing this as they whzz around at breakneck speed, in and around things in pitch dark, that is pretty amazing “vision.”

Big and Little Bats

All bats are in the order Chiroptera -- an order so large that it includes more than 20 percent of all known mammals -- but within that order, exist two distinct suborders of bats, the Megachiroptera, or big bats, and the Microchiroptera, or little bats. Among the many differences between the orders one stands out. Members of the order Megachiroptera all have large eyes and are almost entirely dependent upon their ordinary vision to see the world around them, while the Michrochiroptera have small eyes and rely more heavily on echo-location to see. Members of Megachiroptera are exclusively New World tropical species, such as the large fruit bats, while the Microchiropterans exist worldwide in diverse habitats.

When Echo-Location Plays Second Fiddle

Sometimes bats really need to see the old-fashioned way -- with their eyes. In addition to needing to move around during daylight hours ocassionally, where echo-location is something in the nature of high-tech overkill -- some bats engage in elaborate courtship and mating displays. It hardly does a bat Romeo any good to deck himself out and pull a show-stopping routine if Juliet bat can't see him.

Hair-Raising Maneuverability

Bats don't want to lay eggs on, or get tangled up in, your hair. In the first place, as mammals, bats do not lay eggs but give live birth to their young. In the second place, anything that can zoom around in the dark -- grabbing nearly invisible insects out of the air at lightning speed while dodging trees and buildings -- is not likely to run into anything as large as a human accidently, let alone get tangled up in human hair. If a bat dives toward you, it's more than likely because something tasty that you can't see just appeared on the bat's menu right in front of you. Don't worry, he knows you're there and he'll grab the snack and be on his way before you can duck.