Spider eyesight

[djscho]

This post seems on brand considering iNat’s recent spider theme…

A few days ago my partner found this little spider on the water surface of a rinse tank. I grabbed my camera and was delighted to have it quickly identified, especially since it’s a new species for me:
https://www.inaturalist.org/observations/190329553

It has a distinctive eyesight array with two pairs quite far back and on the top and it got me thinking that this must give it an advantage for hunting or detecting predators while it’s on the surface of water.

This led to me thinking about all the other spiders and their eyesight. I know that good pictures of the eyes can help with identifying and different types of spiders have different eye formations - I believe that jumping spiders have a larger, binocular-like, forward facing pair that help with judging depth.

So I want to start this thread about spider eyes. How the eyes differ between families and what benefits this provides for their particular lifestyles. Share any particularly good observations you have of spiders staring you down. Cool spider visual facts.

Here’s spidery observation I thought was really cool.
On the second photo you can see the eyes have rotated fully around (or covered by a film?) and I have more photos somewhere of the eyes halfway between blue and black. Can this spiders actually see through it’s own body?! https://www.inaturalist.org/observations/110455730

A final thought, how did the spider in the first observation get the common name of Wolf Spider? More confusingly, why is this species in the genus Bear Spiders which is in the family of Wolf Spiders? Why wolves and bears?

[pmeisenheimer]

I’m not anything like a spider expert but that jumping spider is seriously cool.

[whaichi]

@djscho

Here’s spidery observation I thought was really cool.
On the second photo you can see the eyes have rotated fully around (or covered by a film?) and I have more photos somewhere of the eyes halfway between blue and black. Can this spiders actually see through it’s own body?! https://www.inaturalist.org/observations/110455730

I noticed something similar in my observation of Lyssomanes viridis (link). A little searching on Google came up with this article, which talks about how jumping spiders “use green light to gauge the distance of their jumps”.

Most jumping spiders have four sets of eyes. The key to their athletic prowess appears to be the main eyes in the centre. In the 1980s, studies showed that the retina of these central eyes are very unusual - having four layers of photoreceptor cells instead of the normal single layer.

The Japanese scientists knew that the spiders were not using ‘binocular vision’ to measure distance. This is the main technique we use, where each eye gives a slightly different picture of the scene and the brain can then work out how far away things are.

The spiders were also not using ‘lens accommodation’ - thickening or thinning of their lenses. The spider lens is “in a rigid cuticle and therefore not able to be altered in thickness”, says Terakita.

They weren’t using ‘motion parallax’ either. This is used by insects such as the praying mantis, which sways back and forth thus giving itself different pictures of the object.

This left scientists wondering how do spiders measure depth.

Terakita’s team examined a mechanism known as ‘depth defocus’, where the depth (or distance to an object) is determined by measuring the fuzziness of its image.

Their first discovery was that the two deepest layers of the retina only had receptors for green light.

Whether or not an image is focussed depends on two things: the wavelength (or colour) of the light, and distance between the lens and the layer of photoreceptors. Other scientists had already noted that green light would only be sharply in focus in the deepest retinal layer. In the next layer, which is a little closer to the lens, green light would be ‘defocused’ giving fuzzy images.

You might also be interested in this article, which also talks about visual perception within jumping spiders (as well as other forms of perception):

• See the world through a jumping spider’s eyes — and other senses

Perhaps also worth a read:

• Surprise: Jumping Spiders Can See More Colors Than You Can

It’s part of a caption to a picture rather than an in-depth explanation, but this article - Seen any jumping spiders lately? - mentions:

The green eyes are a result of colour-blindness. By limiting their sight to blues and greens, they can detect camouflaged prey more easily. While this would be an impediment to primates trying to find ripe fruit, it gives jumping spiders better vision for prey detection.

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Concerning the name ‘wolf spider’, it’s meant to be a reference to their habit of actively hunting prey - described as ‘stalking’ and ‘chasing’ in different places - rather than relying on a web or ambush tactics to get a meal.

Not sure what the story is behind the ‘bear spider’ name, though the English common name matches the Latin binomial – Arctos. There’s a species of spider here in South Korea with the Korean common name ‘raccoon dog spider’ so it seems people across the globe aren’t averse to comparing spiders to mammals in Carnivora. :)

[djscho]

Brilliant, thanks for such an awesome reply! This is exactly the kind of stuff I was looking for. The stuff about the depth perception is really cool.

[dendroleon]

Many wolf spider genera are named for vertebrate predators + ‘osa’ (as in Lycosa). Some other examples include Pardosa, Alopecosa, Tigrosa, Crocodilosa, and Mustelicosa.

[sebastiandoak]

As you would expect from an active hunter which needs to jump on prey, salticids are some of the most visual spiders. One genera I know which takes it to the next level is Portia.

" The main eyes focus accurately on an object at distances from approximately 2 centimetres (0.79 in) to infinity, and in practice can see up to about 75 centimetres (30 in)… P. africana relies on visual features of general morphology and colour (or relative brightness) when identifying prey types. P. schultzi 's hunting is stimulated only by vision, and prey close by but hidden causes no response.P. fimbriata use visual cues to distinguish members of the same species from other salticids.

Cross and Jackson (2014) suggest that P. africana is capable of mentally rotating visual objects held in its working memory.

However, a Portia takes a relatively long time to see objects, possibly because getting a good image out of such small eyes is a complex process and requires a lot of scanning. https://en.wikipedia.org/wiki/Portia_(spider)"

Other ambush hunters which may have okay vision, often still seem to rely on vibrations and things moving by closely.

https://www.inaturalist.org/observations/179584482

“net casting spiders” also seem quite visual in thier approach to catching things.

Different species than the on I shared here but

" In Florida, Deinopis often hangs upside down from a silk line under palmetto fronds during the day. At night, it emerges to practice its unusual prey capture method on invertebrate prey. Its eyes are able to gather available light more efficiently than the eyes of cats and owls, and are able to do this despite the lack of a reflective layer (tapetum lucidum); instead, each night, a large area of light-sensitive membrane is manufactured within the eyes, and since arachnid eyes do not have irises, it is rapidly destroyed again at dawn." https://en.wikipedia.org/wiki/Deinopidae

[lgarriga]

I don’t have much knowledge surrounding the purposes and benefits of each arrangement of eyes and how it differs for spider genera, so I’m mostly just here to share photos.

Of course, Lyssomanes viridis is a favorite (they’re just so easy to find in my area and are large so they show up with high detail).

But I also have some other jumping spider photos like the Hentzia jumping spiders I tend to run into:

(All images are links to the observations)

Some of the more common spiders in my area have fairly small eyes and I don’t have any photos of Deinopis spiders which I hope to find eventually

[huttonia]

It may seem a tad bit late to continue the spider eyesight discussion, but I have something interesting to say. Most people I’ve talked to before expected spiders with large eyes to be the only spiders with decent vision, but the truth is even spiders with tiny eyes can have extraordinarily decent vision.

Xysticus cf. ferox (family Thomisidae).

Philodromus cf. vulgaris (family Philodromidae).

Good examples are Thomisidae and Philodromidae, the crab spiders and running crab spiders, respectively. From personal experience, both react to movement of camera shutter and blast from the speedlight, especially Thomisidae, like Xysticus, that with rise into a threat display upon seeing the shutter’s movement or speedlight’s flash. I have even seen Xysticus follow my finger as I moved it from side to side in front of its face. Philodromidae typically runs as a camera approaches but doesn’t seem to care quite as much as Xysticus when it comes to shutter movement or speedlight blasts.

There may also be spiders that have excellent vision, but we just don’t know it. Oxyopidae, for example, have excellent vision, proven by males dancing to the females, but they hardly respond to movement in front of them, movement of the camera shutter, or blasts from the speedlight.

Some spiders also have truly weird but fascinating eye modifications. One notable example is the cycloctenid genus Plectophanes, which has a periscope-like projection on its face bearing the eyes. It sits and waits in a retreat but with its periscope sticking out from the hole, just waiting and watching for passerby prey. So the name “periscope spiders” is certainly apt.

Some spiders that probably have poor vision still have equally strange eye modifications. Members of the linyphiid subfamily Erigoninae often include males with weird projections on the eyes or strange eye stalks, but these are only used for the female to grasp onto with her fangs as the male mates with her.