No. 2877: WHAT BEES SEE
by John H. Lienhard
Today, what does a bee see? The University of Houston's College of Engineering presents this series about the machines
that make our civilization run and about the people whose ingenuity created them.
The bees have found the lantana in our yard. And they put
on quite a show as they dine upon it. But today, I find myself looking at their
large black oval eyes and wondering just what they see. That same question goes
for all the creatures out there. What do the orb weaver spiders see, or the paper
Bees, dragonflies, and wasps all have
Remember "Who Killed Cock Robin"? -- the lines,
"Who saw him die? I, said the Fly, with my compound eye, I saw him die."
Well, that fly would've made a very dubious witness. The resolution of its compound eye
is quite poor in comparison with ours. It turns out that such an eye would have to be
as big as a house to match the resolution of your eyes or mine.
And a bee's color spectrum
is "hotter" than ours. It sees higher frequencies of light. You and I see from violet through red. Bees see from ultra-violet through orange.
They don't see the colors in plants the way we do. A flower might be yellow or white to our
eyes. But those plants have ultraviolet pigments that call out to bees, and guide them
to their pollen-bearing parts.
There's more: Bees, flies, and wasps typically have five, not two, eyes. Where are the
other three, you might wonder. The typical arrangement is that big pair of compound eyes,
with a little triangle of tiny
between them. An ocellus is a kind of elementary single-lens eye that doesn't
delineate form. But it does sense light and dark with great speed. Ocelli help flying
insects control flight and detect trouble.
Inset above right: The ocelli of a carpenter bee appear as the triangle of three
black dots between its compound eyes. Directly above: The eyes of a paper wasp. The
ocelli are the three black dots forming a triangle on its forehead.
Spiders don't have compound lenses. Usually, they just have
six or eight ocelli in two
rows. Two of those are more developed than the others and can distinguish prey. These
ocelli are hard for us to spot with our own naked eyes. We're generally aware of them
only when we have close-up photos.
By the way, birds don't have ocelli. But, like bees,
they do tend to see things further
into the ultraviolet range than we do. And, like bees, they can discriminate faster
movement than we can. A bird or a bee watching TV would see a sequence of images,
where we merge those flickers into a continuous movie. That's probably true for our
dogs and cats as well.
A subtle message lurks in all this. Our knowledge, our science, all begins with our
own sense perception. Meanwhile the creatures just outside our doors (or pets with us
inside) -- they live in another world entirely.
We have a so-called
that's meant to free our knowledge from the limitations of senses and emotions. Do we
succeed? Well, yes, to some extent. But watching these complex co-inhabitants of our
flower garden raises a warning against complacency. What that bee, working away in the
lantana bush, sees feels and hears, would be unrecognizable to you and me.
I'm John Lienhard at the University of Houston, where we're interested in the way
inventive minds work.
For source material, click on the links in the text. See also, this
account of insect vision.
All photos by John Lienhard.