How you ever wonder about spider vision?
Ironically, most spiders have very poor eyesight despite having 8 eyes (some have more eight, some less than six) especially those that wait for their preys in fixed locations (such as leaves, flowers and windows).
Other than detecting swift motion, their spider vision can do nothing more than spotting changes in the environmental light intensity.
This function exists so that they can know when is the time to do their nocturnal activities such as hunting, weaving their web or shift location.
Some spiders have eyes that can detect polarized light which they use to navigate while hunting.
But generally, these lay-and-wait spiders do not depend much on their eyesight to hunt.
The average spider which you see sitting on the spider web around your house or in the garden, rely primarily on smelling, touching, tasting and extreme sense of vibration to find their preys.
They wait for the slightest movement or vibration from their webs (which signaling a prey is being caught) and move quickly to paralyze the prey.
Some of them have such keen sense for vibration that they can detect prey under the surface of water, in the soil and even changes in air pressure.
One such example is the fishing spider (Dolomedes) which detect vibration on the surface of water and scoop up any small fishes that swim within its range.
In case you are wondering....
Nope, they do not have ‘spider sense’ like Peter Parker do (makes you wonder which gene of spider did he inherited it from).
Spiders do not have sixth sense to anticipate danger.
If they do, you and I will have big problems clearing these little crawlers out from our house.
However, few unique hunters do have good spider vision. These spiders are specialized in hunting and good eyesight is vital in catching their preys.
There are 4 type of hunting spiders with good eyesight which include jumping spiders (Salticidae), wolf spiders (Lycosidae) and net-casting spiders (Deinopidae).
But before we move on to jumping spider vision capability, let’s understand the eye arrangement of typical hunting spiders.
Eyes of the spiders are placed in various arrangements. In fact, these differences are used to help classifying spider species.
For hunting spiders, the pair of eyes in front of the face, particularly the largest ones, are called anterior median eyes (AME) or direct eyes.
And the rest of eyes are considered as secondary eyes which include anterior lateral eyes (ALE), posterior lateral eyes (PLE), posterior median eyes (PME).
AME are typically used for color and clear vision whereas the secondary eyes are responsible for night vision, peripheral vision and motion detection.
Jumping spiders (Salticidae) are most active in the day.
They have sharp color vision (even ultraviolet light) and are good at distinguishing different shapes.
Their excellent eyesight enables them to hunt preys and identify mates and enemies.
They are utterly amazing hunters.
Other than having good eyesight, these superb hunters have almost 360 degree of vision. My guess for the ‘spider sense’ inspiration.
When hunting, they use 3 different sets of eyes.
Wolf spiders (Lycosidae family) are nocturnal hunters and they don’t build webs. Their eyes are arranged in three rows with four small eyes in front for direct vision.
The second and third rows consist of four huge posterior eyes that are lined with tapeta to help them detect prey’s movement in dim light.
Tapetum (tapeta for plural) is a reflective membrane at the end of the retina which reflect light back to the retina so that the image is intensified.
Wolf spiders are easy to be found at night because when you shine light into their eyes, their eyes glow as the light is reflected to back you.
Similar effect as you shine lights on the eyes of cats and dogs.
Wolf spiders have excellent depth perception for objects at close range which make them deadly hunters. They are able distinguish ultraviolet light which cannot be captured by human eyes too!
Other than hunting, wolf spider vision is critical for identifying the opposite sex during courtship. I guess insects don’t want to get on the wrong bus either.
An amazing hunter that actually catches its prey like Peter Parker shoots his web-ball.
This nocturnal hunter from the Deinopidae family have eight eyes including two rear eyes (PME) that are enormously huge.
With their face curved forward, the eyes looked like two searchlights, giving the spider a menacing appearance.
(Do note that the net-casting spiders have eight eyes, the other four cannot be seen from the front view.)
That is why net-casting spider is also known as Ogre-face spider.
With its size, these eyes are specialized for providing outstanding night vision. They have enormous, compound lenses that give a wide field of view and gather even the tiniest amount of light very efficiently.
In fact, the lenses make web-casting spiders more superior in concentrating available light than a cat or an owl.
To enhance night vision, large amount of light sensitive membranes are produced in these spider eyes every night and rapidly destroyed in the day.
This extraordinary combination of huge light gathering eyes and nightly production of light sensitive membranes allows net-casting spider to pinpoint and ‘net’ their preys in dim light.
Interestingly, net-casting spiders hunt in the light without the help of tapetum (refractive tissue at the back of the retina).
Instead, they place white faecal spots on a surface across which prey animals are likely to walk (such as a broad leaf and a tree trunk).
These spots serve as aiming points and the spider lies above and wait.
So do spiders have good eyesight?
Nope for majority of them. Most spiders can’t do anything more than detecting movements with their spider eyes.
However, some have greatly evolved vision to cater for their hunting style which can be even more sophisticated than ours.
Next time you see a jumping spider staring at you, it might be sizing you up.
Give your best pose.
Anything you wish to add on? Do you know of other spiders with sophisticated vision system? Share it with us! We will love to hear from you.
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