Cicadas: What’s Up With Their Eyes?

It’s just uncanny how insects seem to be looking right at you. No matter how you turn them, and from no matter what angle you look at them, they always seem to be looking right at you.

Right

at

you!

So, what’s up with their eyes? I mean, we “know” they’re compound eyes and that they are quite different from our own. Our eyes are basically a clear-jelly-filled ball, with sensors (retina) at the back, a lens-covered, expandable aperture (pupil) in the front, and muscles that rotate it (so we don’t always have to turn our head in order to look around).

But their eyes are quite different. They are fixed; they don’t rotate. So why does that dark spot on their big, buggy eyes seem to follow around, so it’s always looking at the viewer?

Wet or dry . . . they always are looking at you.

Even while they’re molting!

How does this work? It’s caused by the structure of their compound eyes. It’s essentially a result of tubes, shadows, and mirrors. To understand this, imagine a model: Think of their globe-shaped compound eyes as a cluster of narrow tubes, all pointing outward from a center point, and imagine these tubes are coated, on the inside surfaces, with silver. Closest to you, the tubes are pointed directly at you, and you can see into the whole long (dark) tunnel (you’re not seeing much of the silver), while the tubes increasingly angled away from you appear light-colored, reflecting the light.

That’s basically it: you are looking at a spherical cluster of tubes.

And it’s not just with cicadas; many insects have compound eyes that have this property.

Like this common meadow katydid.

Like this little baby, gray short-horned grasshopper. So cute, sitting on a leaf in his prairie.

And like this pretty green planthopper.

The next question is, why does this seem so freaky to us?

We humans—with our social nature, our interdependence, our allies and enemies, our capacities for trust and for deceit—have evolved to be masters at evaluating each other. We look carefully at one another’s eyes. You can tell so much about someone by their eyes! Yes, “the eyes have it.”

This is why those professional poker players so often wear mirrored sunglasses—they want to conceal their thoughts and feelings. (Why shouldn’t that be considered cheating?)

It’s why people who have eye-alignment problems have a real social disadvantage, because crossed eyes or other misalignments are stereotyped as a sign of severe developmental disability, or head injury, of being dazed or semiconscious.

It’s why silent movie actors wore such heavy eye makeup.

And so we, in our anthropomorphization of insects, can’t help but look into their eyes, too, and try to read their expressions. And what we get back is an unblinking stare, perpetually fixed upon us. Does it freak us out?

Maybe it should. Insects depend on us to not ruin the world for them. They need elbow room. They depend on the existence of their many native food plants; they depend on the habitats—prairies, woodlands, glades, wetlands—that support their various food plants. They need plenty of plants and habitat, because the usual existence strategy for insects is to create a bazillion eggs and offspring, most of which won’t make it to adulthood. On some scale, they need room, like cicadas, to have a bloom, a heyday, and then have a majority eaten by countless predators, and then return to the soil.

So yes, they depend on us.

If you feel stared at, it’s not surprising.

Do things to preserve and increase native habitats.

And vote for the environment.

The above text explaining the dark dot in insect compound eyes is loosely edited from a page I wrote for MDC’s online field guide, Mantids (Mantises). Mantises, of course, are one of the many insects with compound eyes that exhibit this phenomenon.