What do spiders see? September 7, 2011Posted by ourfriendben in critters, homesteading, wit and wisdom.
Tags: blog humor, spider eyesight, spiders in the house, wolf spiders
Our friend Ben became intrigued about exactly what spiders see after Silence Dogood had an encounter with a spider in our bathroom last night. This led to the following rather unfortunate exchange:
Silence: BEN!!! There’s a HUGE spider in the bathroom!!!!!
Our friend Ben: Oh? What does it look like?
Silence: It’s big, brown, and hairy.
OFB: A tarantula, no doubt.
Silence: That’s NOT funny, Ben! That spider charged right at me!
OFB: Really? Hmmm. You know how spiders have all those little primitive eyes on their heads. I wonder if it actually saw you, or was attracted by your body heat…
Silence: Listen up, Sherlock! Either you get in there right now and deal with that spider, or I’m going to deal with you!
OFB, already heading, not to the bathroom, but to the computer to check up on spider vision: Uh, Silence, did you say something?
Let’s just say that some time later, I was able to go online to see if I could learn more about exactly what spiders see. Heading to my good friend Google, I landed at a site with exactly the information I needed. In an article called “How spiders see the world,” the Australian Museum discussed arachnid vision, not just in spiders in general, but in detail for specific spider groups. If you head over to http://australianmuseum.net.au/How-spiders-see-the-world, you can read all about it.
But to sum up, the site notes: “Spiders usually have eight eyes but few have good eyesight.” It goes on to say that “They rely instead on touch, vibration and taste stimuli to navigate and find their prey. Most are able to detect little more than light-dark intensity changes… The direct eyes appear dark, whereas the indirect eyes usually have a layer of light reflecting crystals, the tapetum… giving these eyes a silvery appearance. The tapetum increases visual sensitivity… intensifying the image…. Spider eye lenses are better than photographic lenses in terms of their image brightness… However, because most spider eye retinas have relatively coarse-grained mosaics of receptor cells, their resolution of these images is much poorer than in the human eye.”
Some spiders do have pretty good vision, however, including wolf spiders, such as the one that was terrorizing Silence. The site notes: “Most wolf spiders (Lycosidae) hunt in the dimmer light of dusk and moonlight. Their four large posterior eyes have well-developed tapeta which help them spot prey movement in such low light conditions.”
So, did the wolf spider actually see Silence, blinded as it probably was when she switched on the bathroom light? Or did it sense her? I guess we’ll never know. But, all you spider-lovers out there, fear not: No spiders were harmed during the making of this post. The spider was captured (via a jar over the top followed by an index card slid underneath) and returned to the comparative wild outside. Our friend Ben knows both it and Silence were greatly relieved.