Today’s Wonder of the Day was inspired by Tania. Tania Wonders, “How many eyes does a spider have?” Thanks for WONDERing with us, Tania!
Little Miss Muffet: Hey Spider! What are you up to?
Spider: Not much. I was just spinning a web and saw you sitting here on this tuffet. What are you eating?
Spider: Can I try some?
Little Miss Muffet: Sure! Pull up a tuffet and I'll share the rest of my bowl.
We had to get going, so we weren't able to stick around to find out whether the spider liked the curds and whey. Their conversation did make us curious, though. Exactly how was the spider able to spot that bowl of curds and whey from a ways away?
Some spiders can't see at all. Most spiders don't see very well. Many have eyes that only help them distinguish between light and dark. Only a few species can see well in enough detail to be able to hunt prey effectively.
Those facts may surprise some people. Why? Because spiders have so many eyes! Most spiders have eight eyes. Some species have six or fewer eyes, but they always come in an even number.
Some species of spiders, such as those that live in caves or under the soil, have no eyes at all. Even those species with eight eyes don't usually see very well. For example, most spiders that spin webs have poor eyesight and rely upon their senses of touch and smell to navigate their webs and find prey.
Unlike insects, which have large, compound eyes (that is, eyes with multiple lenses), spiders have simple (single lens) eyes that are more like those of human beings. All those eyes don't necessarily work the same way, though. Many of them are specialized just for certain tasks.
For example, jumping spiders are known for their sight, which they need to hunt for their prey, since they don't spin webs like other spiders. Their main eyes, called principal eyes, look forward from the middle of the head. They provide clear vision, possibly even in color.
Moving outward, the next closest eyes provide depth perception but not focused vision. Moving outward even further, the eyes along the side of the head are used primarily to detect movement in the peripheral range.
Other spiders have also developed eyes specialized for their needs. Wolf spiders, for example, usually hunt at night. Their eyes reflect light, which helps them to hunt in low-light conditions. The way in which the eyes are arranged on a spider's head also varies between species depending upon what and how they hunt.