If something really small with eyes, like an ant, were to stumble upon something very small humans can’t see, would they be able to see it?
In: Biology
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I’m wanting a biologist to respond but my pick is they will have developed senses to detect the things that eat them and that they eat. But the smaller the creature, the less body there is to develop complex vision systems so the question itself starts to fall down. They will have ways of sensing important things, but probably not in the way you are thinking.
(Minor edit – phrasing)
Other commenters have accurately pointed out that many microscopic organisms don’t have eyesight per se, and use other means of sensing to detect objects around them.
Of animals that do have eyesight, it is not the size of the animal that determines the size of object which can be seen with the naked eye – it is the magnification and proximity.
Magnification:
Some animals have the ability to magnify objects more than humans can by essentially flexing muscles in their eyes to change the shape of their lens, as well as having good reactions to light which help narrow and focus their vision (birds of prey can do this, for example). So if you and a hawk were flying along at the same height, they could see smaller things than you could, because they have better magnification.
Proximity:
If animals are very small and close to the ground, they may be able to pick out smaller objects and see in more detail because they are closer to them than you are. If you and an ant are both looking at the same patch of ground, and you are standing up, the ant may be able to pick out details that blend into the background for you. If you were to lie down on the floor and look at a very small patch of ground, you would be able to pick things out in roughly the same amount of detail, because you are much closer to the same proximity to the ground.
If you were an ant sized human would you be able to see smaller stuff?
# ELI5
Small organisms with eyes can’t see small things humans can’t see because their sight isn’t as good. Small eyes can’t have as good sight as large eyes can have because light bends while passing through small apertures and that distorts the image.
# More elaborate explanation
Human eyes have certain aperture (the hole through which the light passes) size and it determines how much light is diffracted while passing through the aperture. [Diffraction](https://en.wikipedia.org/wiki/Diffraction) is bending of light waves while passing through an aperture. Light diffracts more in smaller slits. The size of human eye aperture allows to [see with the resolution of around 1 angular minute](https://en.wikipedia.org/wiki/Naked_eye#Basic_properties). Smaller animals with non-compound eyes therefore have worse sight than that.
Insects use [compound eyes](https://en.wikipedia.org/wiki/Compound_eye), where each light sensor is in its own tube and with its own lens and detects only light travelling rougly in the direction of the tube. These eyes are simpler in construction than non-compound eyes and have low resolution. But, if insects had non-compound eyes, they wouldn’t see better because their eyes are so small that the diffraction would make the eye’s resolution as low as it’s in their compound eyes.
# Caveat
It could be said that smaller eyes can get closer to the seen object, therefore see it in a larger angle. An insect with could see an object as small as one ommatidium in its eye, which could be very small in small insects, if it was placed right next to the eye. But then it could be said that humans can see tiny [eye floaters](https://en.wikipedia.org/wiki/Floater), particles floating in the vitreous body of an eye, which can get so close to the retina that they can be seen although they are so small.
If you take a penny and hold it one inch from your eye, you won’t be able to read the date on it, because human eye binocular vision isn’t really built to visualize something that close. And relatively speaking, a penny is huge.
An ant, and other tiny things, are more likely to have evolved to see things a millimeter in front of them, so yes, I’m guessing an insect would be able to see a crumb of a crumb of cake that a human wouldn’t.
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