My eyelids are swollen/drooping?

Why the insects lack of eyelids has to do with their inability of closing their eyes?

• Edit/Up-front: A classical example of a translation mistake. I could delete part of this mess and save myself from the great mortification I'm feeling but this example of mistake can help remind us to never jump on conclusions about the other... Idiom, cultural differences, momentary difficulties, etc. Underneath we're all the same, aren't we? ... Almost the same?? :) Okay Raquel, one thing is called eyelid, the other, eyelash. Thank you, anon, I don't think I'll be able to forget this lesson:) ------- To post questions in English is one of my weakness. Usually there's an angel that passes by and edits it... I've heard here on Quora 'insects can't close their eyes because they don't have eyelids'. And since I've heard it, the insects around here are afraid of me staring them intrigued. My friend with cancer (no eyelids) told me to bug off, the insects can't. What I'm asking here is, what is the relation between: no eyelids = no closing eyes. From school days, I know they work as protection from dust and excessive light. But I've met people (not insects, ok) without eyelids and still able to close their eyes... So, behind the question is this kid here thinking... why humans can close their eyes and blink naturally without eyelids and insects can't? The blinking action isn't enough to provide humidity to the eye? Why insects can't blink their eyes providing this necessary humidity... Maybe just maybe, it is not the absence of eyelids but the non blinking that makes it "impossible" (the word used here on Quora)?  Who's really to blame first: the lack of eyelids or the lack of blinking?

• Answer:

  Well, you can't close an eye without an eyelid. So, rephrase the question: why don't insects need eyelids? Lots of animals have eyes, but these come in two forms. One form appears in the deuterostomes: a group of animals that contains starfish and sea urchins, but also fish, reptiles, birds, and us. The other eye form exists in the protostomes, which include molluscs, worms, spiders, and insects. These two lineages diverged early, and each's eyes evolved on their own unique tract. It is proof of evolution that protostome-type eyes never appear in the deuterostomes, and vice versa. Our eyes evolved from fish eyes, since we evolved from fish. Fish live underwater, and their eyes work best when wet. Even though amphibians and other animals up to humans now live above water, we never lost this requirement for eyes to be moist… something an intelligent designer wouldn't have allowed. We have eyelids to keep sand and grit our of our eyes and to keep the eyeball moistened by spreading tears over it. Without eyelids, our eyes would dry out and quickly stop working, which is why staring contests are so painful. Insect eyes are different. Instead of a single eyeball with a lens, insects have compound eyes, or individual ocelli. Think of a compound eye as a retina folded outwards. There is no liquid in an insect eye: the cells go all the way down. And the outside of the eye is exoskeleton, so it's hard and armored: no need to worry about water or dirt or sand. They don't need to blink because their eye is not a bag of fluid and, like their bodies, need not be kept moist. UPDATE: It seems the original poster meant to say "eyelashes" instead of eyelids. Well, eyelashes help clean the eye and also detect if something is getting too close to the eye: they're like smaller versions of cat whiskers. Insects don't have hair or eyelids… but some do have bristles near their eyes that are used for sensing! Of course, they have these bristles all over their body, so they aren't true eyelashes. In this photo, the antennae (with their bristles) are on the left, but the other black filaments you see are sensory bristles.