An animal’s eyes have the power to speak a great language.
I went out the other day to grab one of the hummingbird feeders for a refill and a slight movement caught my eye. It was a bizarre-looking jumping spider on the metal bracket that held the feeder.
What struck me about this one was how hairy it was and the way it moved. As I watched, it did what many jumpers do when you get close – it turned and faced me, apparently looking back at me.
Although I wanted to photograph it from the front to try to catch those eyes, I figured I needed a picture of the dorsal surface in order to identify it. Later, as I searched Bug Guide, I realized this one was a tough one as there are many jumpers with similar markings. I finally settled on it being a male Phidippus putnami (referred to as Putnum’s Jumper by one reference). Now that we have that detail taken care of, let’s look at those eyes.
Jumping spiders are in the family, Salticidae. All members of this family have four pairs of eyes, with one pair (the central ones when viewed from the front), being particularly large. These are known as the Anterior Median eyes. Studies have shown that the different eyes have different functions. The smaller, posterior eyes, have relatively poor vision and probably serve to provide light and dark reception as well as to detect movement. They also provide the spider with a 360 degree view of its world. The Anterior Lateral eyes seem to provide some visual details but may serve primarily to alert the spider to looming threats (the “looming” response is when the spider retreats rapidly as something approaches it, a safety response). The Anterior Median eyes have the best vision, but a very narrow field of view. The eye lenses are attached to the carapace and therefore cannot be moved like our eyes. So, in order to look around and focus on something, the spider either must move its body, or, if it is something just off to the side a little, small muscles can move the retina while the lens stays fixed.
You can sometimes look into those large eyes of a jumping spider and see them change color as it moves the retina around. You will know when it is looking directly at you, those eyes will appear their darkest.
This little guy was fascinating to watch. He was very alert and moved fairly quickly through the vegetation. He seemed to like to climb anything vertical in his path so I put a rock in his way at one point to try to get a clearer picture. He went up on the tip and looked around, giving me a chance at the two images above. I also noticed he would turn, raise his pedipalps (those things that look like short legs with swollen tips under his eyes) and then jump toward some other noticeable point in his environment. I really wanted to try to get a photo of him jumping, so I moved the rock in front of him a few times as he moved across the yard, waiting until I saw him raise his pedipalps, and then firing the camera.
Turns out he is much quicker on the jump than I am on the shutter, so this is the closest I came in three tries at capturing his leap. That is part of one of his hind legs in the upper right corner. But it does show how these spiders always leave a safety line of silk as they move or jump. Not a bad life plan really…look before you leap, and always leave a safety line, just in case. I think I can learn something by looking into those eyes.