Do insects with compound eyes have depth perception? They fly as if they do, but their eyes are so close together it seems like the image would be 2 dimensional.
"1001 questions answered about insects" by Alexander Barrett and Elsie Broughton Klots includes the following passage:
Do insects have depth perception? Depth perception of some sort is important to an animal who has to catch its prey; fortunately most insects have it to a degree. Although they do not have binocular vision that can be compared with man's, it is true that when one eye is covered their depth perception is markedly affected. The criterion of depth seems to depend on the angle of simultaneous stimulation of two corresponding points of the retina of the two eyes.
However it does not mention compound eyes specifically.
There may be other methods of obtaining a perception of distance rather than the binocular vision seen in humans. This paper suggests that there is 'clear evidence' that some insects perceive depth by moving their head to artificially create parallax, which they can then recognise and interpret as depth and distance. They cite the Praying Mantis as an example, which does have compound eyes.
(Newcastle University, England) [source]
Stereopsis = the perception of depth and 3D structure obtained from visual info from 2 eyes.
Vertebrates (including humans and all primates) use stereoscopic vision to perceive depth. Each eye sees slightly different images based on their side-by-side orientation, which allows the brain to "calculate" the difference and generate our perception of depth. This is typically accomplished in organisms with 1+ billion neurons in the brain.
Nityananda et al. (2018) have confirmed for the first time that an invertebrate (with only ~1 million neurons) also is capable of stereopsis.
- Work by S. Rossel (and others) as early as 1983 had previously suggested this was the case.
Specifically, their work showed that instead of using correlations of image contrast for stereopsis...
Mantis stereopsis...relies on detecting luminance change at positions corresponding to appropriate disparities.
In other words, they propose that mantids are looking for changes in the light patterns over time -- basically, they're only looking for movement.
You can read their paper here.
Nityananda, V., Tarawneh, G., Henriksen, S., Umeton, D., Simmons, A. and Read, J.C., 2018. A Novel Form of Stereo Vision in the Praying Mantis. Current Biology.
Khan, Amina. 2018. What do you see when you put miniature glasses on praying mantises? A new method for robot vision. Los Angeles Times. Accessed Feb 2018. http://www.latimes.com/science/sciencenow/la-sci-sn-praying-mantis-vision-20180209-story.html.
Wikipedia. "Stereopsis." Accessed Feb 2018. https://en.wikipedia.org/wiki/Stereopsis.
The sense of depth is required to us to orient ourselves in a 3D world. Insects do orient themselves in the exterior 3D world, thanks to the ability to detect the plane of sunlight polarization, that is used as a navigation compass in foraging expeditions and when coming back home.