This is a fantastic illusion created by Joseph Mohmed.  All you need to do is look at the spiral and then juggle this web page up and down.  A black widow spider will appear right before your eyes!

Did it work for you?


  1. That spider has more legs than normal spiders. I wonder if David Thorne drew it. He is not so good with the numbers when it comes to spider legs.

    1. Stumbled upon this blog post after Googling my name (I’m not the only one who does this, am I?). When I made this a few years back, I actually didn’t notice the spider effect until I e-mailed the picture to an illusion website and he mentioned it.

      The full-size image has some awesome effects. Just staring at the center and moving your head slightly causes random parts of the image to kind of bulge out and distort. And if you stare at it for a little bit and then look at something else there’s kind of a zoom-blur after-image.

      Full-size version:

  2. It doesn’t work with a mousewheel, but by grabbing and moving the scroll bar manually, I too can see a spider-like shape.

    1. yup. i agree completely. still, doesn’t look much like a spider, and definitaly not detailed enough to say it’s a black widow…..

  3. I wouldn’t say it’s a true spider, but it’s spider-like, and may strike fear into the hearts of criminals…

    …much like Spiderman.

  4. I have been in web development for more than ten years, and I actually lifted my laptop so I could juggle the page up and down with my hands. I’m more worried about than than any cyber spider.

    1. I also jiggled my laptop up and down, but I couldn’t do it fast enough. Also, everything looks red now… uh oh…

    1. What Richard describes is a common thing for people who drink too much. They start seeing all kind of weird things. When you do not see it, it proves that you have no drinking problem 😉

    2. Zach don’t pay any attention to Roland he has it backwards…..what this means is if you can not see a spider like shape moving within the image then you have a 99% chance of becoming violently psychic without warning…..but look on the bright side there is a 1% chance you will be just fine… question ….. well maybe two questions… you feel lucky? and what side of the ocean are you on?….. hehehe…..Oh and I do see that creepy crawly looking thing just fine…. :}

    3. Oh crap!!! ROFLMAO that’s the last time I leave my auto spell check on….and stay up all night and post….not always the best combination….but hey throwing things at and trying to kill ghosts will work too….lol….. :}

    4. okay, I sort of see what you’re talking about now. I wouldn’t call it a spider, though. more like a vague spider-like spectre.

  5. Surely must depend on the screen resolution rather than an optical processing effect.
    Similar to net curtains overlapping.
    It is an interference pattern, no?
    When I do graphic design work, I get a similar but unwanted effect when certain shapes are enlarged or reduced, particularly if they are patterned.
    This is a bit like the stroboscopic effects on car wheels and helicopters etc, where the interference is a function of the frequency as opposed to the screen grid resolution.
    I love anything like this. So much of what we percieve is an approximation and while this is not a perceptual illusion (is that the right term?) it does shed some light on the limitations of visual perception.
    Like noise cancelling headphones. Like radio telescope arrays that produce a much greater resolution than the sum of the parts. The interactions between two frequencies create wonderful effects.
    Or when you point a camera at a tv – you get not only the stroboscopic effect but also a patternation that swims and shifts almost randomly.

  6. Interesting – jiggling the page up and down presumably moves the image faster than the eye can track it, thereby creating a transient moiré pattern:

    Oh, and also, following previous images, I traced the first few rotations of the spiral to double check it was a spiral and not a series of concentric circles 🙂

  7. I saw a vague image that could be described as slightly spiderish. Know what it is going for but didn’t find it especially stunning.

  8. hmm… Can’t quite work out how to move it up and down on my screen effectively (tried mouse and scroll bar) – and there’s no way I’m waving my 22″ Cinema Display around! :-O

    I saw the beginnings of ‘spider legs’, though. Maybe if I printed it out… :-/

  9. It works if I use the keyboard to jiggle the screen, not if I use the mouse; but it’s not a particularly dramatic effect.

    Saying that though, I can’t always see some of the moving effect patterns you post here, probably due to the slight astigmatism in one of my eyes; so perhaps the effect is more pronounced for others.

  10. If I hadn’t known it was supposed to be a spider I wouldn’t have recognized – but I did see an hourglass shape with “legs”.

  11. The only thing I “see” is four vague lobes radiating from the center, at right angles from each other.

    Why is the spider named “Spot?” (har har)

  12. Yeppsies it works for me all right!

    and i found this other thing with it. if you keep staring it for about 20 secs and then press the PG DN (page down) button on your keyboard, the page will look all blurry and kinda zoomy outly

    1. awesome! I uploaded it and going to e-mail it to a friend of mine who is terrified of spiders!! You know that saying about having friends like me …… lol….thanks!

    2. i cant see it when i looked at the one gord posted
      i can only see the one where i break my up and down keys…… :mrgreen:

  13. When I see it the way Gordon, above, posted it, I do get the illusion, but the power of suggestion makes it labeled a spider. Otherwise I would call it a stretched out “8” or sideways infinity sign, ignoring the ultra-faint “legs”.

    Weak illusion, this one. And that’s okay, spiders kinda creep me out. Even illusory ones!

  14. Okay, there is a dramatic difference between different monitors. In my work, I had a LCD and the effect was stunning. In my house, I have a good CRT and the effect is non-existent. I guess the effect has to do with different refresh rates or the way how the pixels are organized between different monitors. I think this rules out an explanation based on optical illusions connected to the form itself (and to the brain and vision system): if it was the case, I should have either seen the effect or not, in both cases.

    To confirm this, can anyone who has access to both kind of monitors report what you see in both? I could have asked for those who see the effect on CRT’s to came forward, but the problem is, if they didn’t saw it too in a LCD, they might think they are seeing the effect, by suggestion power only. The effect is very clear when it happens… and if I had saw the image only at my home, I would have never guessed what people were talking about.

  15. It’s not the refresh rate per se. It’s more like the panel technology. I guess LCD’s ghosting is what makes it work better on those. On my plasma at the same rate (60 Hz) it doesn’t work at all. If you’re on Firefox 3.x, you can click on the pic and drag it a bit. That will produce a “ghost” picture on top of the original one and the moire will be visible.

    1. hmmm… I think you are right. Actually, by refreshing rate I was thinking on parts of the moving image caught at different times, kind of, the top of the spiral belonging to it at one time, the part bellow, to another time… but that makes even less sense: if it was that, the effect would be abrupt, I think, not smooth as we see.

      The refreshing rate has, of course, a relation with the ghosting effect, but only in an indirect way regarding this illusion. So, I fully agree with you.

  16. Sadly, no spider for me, although I enjoyed picking up and wiggling the image (in Firefox) to see the effects.

  17. For the ones who can’t see the effect, there is a simple way of reproducing it in any monitor (with a PC):

    1. Copy the picture for the clipboard
    2. Start the Paint application (which comes with Windows) in the accessories.
    3. Past the image.
    4. In the menu Image, deselect “draw opaque”.
    5. Past the image a second time
    6. Move this second image down a little, and choose the “spider” you like most


    (This uses simple tools which likely will exist in any computer, OS or graphical interface)…

  18. I made a spider and I clicked something 2 c all my windows and it gave loads of different black and white sparkle shaped stars! (the ones wiv 4 points)

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