For a couple of years, I was on a quest to obtain detailed pics, and video, of a peculiar optical trait visible in one particular species of spider; many spiders likely have the same trait, but it’s only visible in the magnolia green. The anterior median (front middle) pair of eyes is used to accurately judge the distances for jumping, and as such are complex eyes, rather than the simple compound eyes that we associate with arthropods like house flies: they can focus and aim like our own, and when I say “like,” I mean quite a bit unlike our own. Since their cornea is part of their exoskeleton and is periodically shed with the rest, it’s fixed in place, so the eyes move internally instead, and because that same exoskeleton is largely translucent for the species, enough light gets through that this can actually be seen. Which is what we’re seeing here – the black circle in that right eye is actually the spider’s retina. Yes, they can aim their eyes independently – can’t you?
This image, and an accompanying video, is the result of planning/staging that went far, far better than expected, or even than it should have. I housed a pair of spiders in a small terrarium and provided a variety of ideal insects as food, and eventually witnessed one of the spiders immediately after a capture – only it wasn’t in a very good position for macro photos, and certainly not for the little USB microscope that I had at the time to do video. Somehow, the spider allowed me to not only lift the plant (that I’d provided as habitat) out of the terrarium without fleeing, but rode along complacently from the porch all the way into my office because the microscope could only attach to the computer. The results are a little disconcerting but very illustrative, so full credit to this spider for its patience. Or, because I’d already worked quite a bit with the species and knew they were as hyperactive and uncooperative as any jumper, giving them food is the secret to having them hold still.