Ask an Entomologist: Do insects have eyes?

This question was relayed to me by Zooilogix from a young reader. The answer is yes, insects do have eyes-they even have two kinds of eyes!

The first kind of eye that insects have are called Ocelli. This photo of a wasp head shows the characteristic arrangement of 3 ocelli in a triangle between the larger compound eyes. Most adult insects have two compound eyes, just like we humans have two eyes.

Both kinds of insect eyes–ocelli and compound eyes– function to detect light and movement, just like our eyes. Unfortunately, there are so many different kinds of insects, and kinds of insect eyes, that a discussion of them all without boring everyone, or sounding like a textbook, is going to be impossible.

So let’s just focus on the cool stuff, eh? I’ll put links at the bottom for the people that really want to know what an apposition eye is. :)

Insect compound eyes are very different–but also similar–to human eyes.kinds of eyes

Human eyes are mostly liquid, and use the iris to adjust how much light gets in. You can see this at work if you look at a bright light and then away when looking in a mirror–your pupil will get smaller and bigger, depending on the light.

Insect eyes are mostly solid, and are made up of many individual parts. An insect eye has a sort of bumpy appearance–some insects have over 40,000 individual units to a single eye, which is why it’s called a compound eye. They use pigments traveling up and down inside the eye to regulate how much light gets in. This can make some really neat patterns on the insect eye. Because the eye is solid, it isn’t as easily injured by a poke as our fragile liquid eyes.

Freaky-cool insect eye modifications:Whirligig beetle

Whirligig beetles (Gyrinidae) actually have 4 compound eyes! Gyrinids live and swim on the surface of ponds and streams. One set of eyes is for seeing above the water, and one is for seeing below the water. (The red line in this photo shows where the water line is when the beetle swims) Oddly enough, these beetles only appear to have 4 eyes–each of their eyes splits in half during development. One half migrates downward onto to the beetle’s chin, and the other to the top of its head.
If you had 2 extra eyes, where would you put them?
You can learn more about gyrinid beetles at Hilton Pond’s website.eye guy

Another neat variation on the basic plan is found in dragonflies. Their eyes just about cover their whole head! What would having a head that’s almost all eyes be like?

Our last example of cool insect eyes is found in a group of flies called Diopsidae. They have their eyes out on stalks!

I’d have a lot of trouble with these kinds of eyes–I tend to bump into things a lot, and it would really be a drag to break one of your eyes off!

So there you go, a very brief intro to insect eyes for a young’n.

Some additional insect vision resources:

More advanced resources:

11 thoughts on “Ask an Entomologist: Do insects have eyes?

  1. aw, thanks! *blush*

    And if I go over your head, please tell me!
    Part of the purpose of my blog is for me to try to practice writing without using science jargon.

    Scientists sometimes speak a different language, which I think is part of reason science is so poorly understood by the general public.

  2. I have been searching the net for studies on ants. I was hoping you can answer one of my questions that i haven’t had any success in finding the answer. Have you or anyone else discovered if an ant can hear or feel human footsteps and if so, at what distance are they able to feel or “hear” them. Any help you can offer will be greatly appreciated.
    Regards,
    Jessica

  3. well, they certainly could feel our footsteps, since we create quite a thump compared to an ant’s size. Our feet also create a pressure wave of air that’s displaced.

    However, I’m not aware of any studies that can answer your distance question.

  4. What percentage of a bug’s head is taken up by its eyes? I figure it varies by insect type, but can you give a couple examples, like a housefly, a Monarch butterfly, and a wasp?

  5. Yep–it can vary quite a bit. An adult dragonfly is almost all eyes–I’d guess (not measuring volumes) the head is about 70% eyes. Deerflies are another group with big eyes.

    Many insect larvae don’t have very big eyes–wasp larvae would be one example.

    To accurately give you a percentage, I’d need to know the volume of the insects’ heads–which I don’t know off the top of my head.

    And it’s a holiday weekend, so I may wait a while until I calculate that :)

  6. Thanks for the info on dragonfly eyes compared to head size. I took some photos of bugs in the back yard and was amazed at the size of the wasp and bee eyes compared to the entire head. Hope you can give me more info. Thanks for looking at my question on the holiday.

  7. It turns out that no one has quantified this in a systematic way. (or at least, not that I can find in a quick search of the literature).

    It isn’t really a useful thing to know in terms of taxonomy or physiology, so that makes sense. There are a lot of keys that have characters like “eyes touching midline of head”, but that isn’t a percentage.

    Scientists seem to have studied the way in which the eyes are arranged, or how many facets they have and how big they are, but not to quantify the volume of a head/volume of eyes.

  8. Dear BugGirl,

    I have twin sons and have a hard time coming up with new or different science projects each year. One of them has decided to use their bug collections but we cant think of what would be a good topic in using the various bugs in their collections. They each have various large butterflies, moths, beetles, locusts, dragonflys, bees and preying mantis’. Can you help?

  9. That would depend on a lot of different factors–what grade are they in? Are they required to do an experiment, or just a display?

    Schools require (and grade) science projects in a lot of different ways.

  10. They are in 3rd grade (9yrs old) and the paper says “research, experiment, model or invention”–which I never noticed before.

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