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If you have noticed a yellow garden spider (Argiope aurantia) dangling off a plant in your yard and wondered; how many eyes do spiders have? The answer would be – It depends on the species of spider you’re watching.
There are over 50,000 species of spiders in the world. With this huge variety, the number of eyes on a spider also varies greatly. The cave-dwelling spider (Sinopoda scurion) has no eyes, while a red-backed jumping spider (Phidippus johnsoni) has eight eyes (four pairs).
Spiders use their eyes to protect themselves from danger, find prey, and judge distances. Spiders also require good vision to recognize their mate, so they don’t devour it.
Why do spiders have so many eyes?
99% of spiders have eight eyes. Let’s learn more about their eyes and how they work.
Spiders have two large front eyes called anteromedial eyes (AME) or principal eyes. Their main function is to focus on an image, like prey.
The principal eyes also allow spiders to judge distance. These large eyes allow for color vision, and some species see ultraviolet light with their eyes, something our human eyes cannot see.
- The pair of eyes next to the principal eyes provide 3D vision and the ability to see how far a prey is. However, this pair of eyes have blurry vision.
- Since spiders have no neck, they cannot turn their heads (or cephalothorax ), and so the AME are fixed. To deal with this issue, spiders have additional eyes in different positions that gives them the ability to almost enjoy a 360° view. There are smaller, side eyes spaced around the spider’s head that act like motion detectors, and alert the spider to movement. These eyes also make the spider aware of the presence of any predator or prey.
Three interesting spiders and how they use their eyes
1. An intriguing spider, Asianopis subrufa, hunts at night using a net. It has excellent night vision due to its powerful eyes, which help it cast its net over its prey.
2. It is believed that dragonflies have the best eyesight among insects but turns out jumping spiders can put even dragonflies to shame with their eyesight!
Jumping spiders have eight eyes. They require a keen vision for leaping and attacking insects. Their main eyes only see what’s right in front of them. Their secondary eyes transmit the exact location of the prey. Their two pairs of eyes function as one.
Jumping spiders can leap anywhere from 10x to 50x their body length to snag their lunch!
3. Wolf spiders are more interested in dining. They hunt at night. Their eyes reflect light back, and this provides them with night vision. If you point a flashlight at a wolf spider, you might catch its eyes shining!
Do all spiders have eight eyes?
Although most spiders have eight eyes, the variety is quite large from spiders with no eyes to spiders with 12 eyes. To answer the question, how many eyes do spiders have, we need to identify the species of the spider first:
Two eyes: Caponiidae family
Four eyes: Symphytognathidae family
Six eyes: Recluse spiders
Eight eyes: Wolf spiders, Jumping spiders
Apart from the number of eyes, the position of the eyes differs from species to species. The position of the eyes depends on the hunting style of the spider, and what they prey upon.
The eyesight of the same family of spiders can be quite different. While the Kauai cave wolf spider (Adelocosa anops) (left) has no eyes, most wolf spiders (Lycosidae spp.) (right) have better vision than most spiders, and some can see well in the dark.
Do more eyes mean better vision?
Very few spiders have excellent vision, no matter how many eyes they have. Most spiders’ eyes perceive changes between light and dark which allows for a quick reaction if a predator is near. For example, if you move your hand over the yellow garden spider, the shadow of your hand would cause the spider to move away. Spiders use touch, taste, and vibrations to navigate their world. Spiders have hair on their body that catches these vibrations (much like how you can sense your hair fly in the breeze).
Spiders in the family Caponiidae are fascinating as they can have two, four, six, or eight eyes. Some spiders of this species grow extra eyes as their bodies mature into adults. In a few of the species, their eyes meet so close in the middle that it looks like they have five eyes.
A Look Inside a Spider’s Eye
The structure of each of these 4 pairs of eyes are the same. Each eye has a single lens attached to a long tube. The tube aims the light at the retina, which is at the end of the tube. The retina is loaded with photoreceptors that are responsible for visual sharpness of an image the spider is seeing.
Next time you’re in a garden and watch a spider closely and count its eyes. While you are observing the itsy bitsy spider make a guess on what it is seeing. It just might be eyeing its next meal.
Hands-on Science:
Test out the strength of spider silk. Find an empty spider web, and choose a strand of silk in it. To test the strength, hang small wire paper clips on the strand, and count the number of paper clips the strand can hold, before breaking.
Glossary
Cephalothorax: the combined head and thorax of arachnids, such as spiders, and of many crustaceans, such as crabs
Ultraviolet light: invisible rays that are part of the energy that comes from the sun.
Anteromedial: located in the front and towards a middle line
Lens: a clear, curved structure at the front of the eye and behind the pupil. It focuses light rays that enter the eye through the pupil, making an image on the retina
Retina: light-sensitive layers of nerve tissue at the back of the eye that receives images and sends them as electric signals through the optic nerve to the brain
Photoreceptors: special cells in the eye’s retina that are responsible for converting light into signals that are sent to the brain. Photoreceptors give us our color vision and night vision.
Flesch Kincaid Grade Level: 7.2
References
How Spiders See the World. June 6, 2022. https://australian.museum/learn/animals/spiders/how-spiders-see-the-world/
Pappas, Stephanie. Jeepers, Peppers, Why Do Spiders Have So Many Eyes? November 18, 2021. https://www.livescience.com/24054-why-spiders-have-eight-eyes.html
Patel, Pyush. How Many Eyes Do Spiders Have and How Do They Work? January 16, 2022. https://www.scienceabc.com/nature/animals/many-eyes-spiders-work.html
Gray, Mike. Net Casting Spiders. July 25, 2022. https://australian.museum/learn/animals/spiders/net-casting-spiders/
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