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No. 2877:
What Bees See

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 wasps? 

Bee over lantana

Bees, dragonflies, and wasps all have compound eyes. 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.

Carpenter bee's ocelliAnd 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 ocelli 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. 

Paper Wasp Eyes
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 scientific method 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.

(Theme music)

For source material, click on the links in the text. See also, this account of insect vision.

All photos by John Lienhard.

Dragonfly on a twig: Note the large compound eye: just to the right of it one can make out one of its beadlike ocelli 

This episode was first aired on April 9, 2013