This maybe too little nine years too late, but here it goes. I read a 2000 column entitled “Can spiders carry rocks?” and the reasoning behind them not being able to seemed sound. However, I know there is at least one type of trapdoor spider who specifically finds and strategically places quartz rocks in and around its hole and trip lines. It does this because vibrations travel better through quartz than they do soil. Dictionary.com defines carry as “to take or support from one place to another; convey; transport.” Now, for all I know, the spider may hold the rock in its front four legs and walk back to the hole on its four hind legs. Or, maybe it somehow hurls the rocks up on its back and balances them water jug style home. Or, maybe it just rolls them. Regardless, doesn’t that meet the definition of “carry?” I don’t think this spider lives in the US, so this probably won’t explain what the students saw. I just think that a spider who carries rocks should have been mentioned in a column about spiders transporting rocks.
Can you point me to the staff report? I can’t seem to find it - obviously my screaming inability to find some obvious link. I have trapdoor spiders in my garden who regularly move stones and bind them around the entrance to their burrows with silk. They do this if they happen to burrow in a gravel path. If they burrow in soil, they will use whatever is nearby. The variety is amazing - I call them my arachnid architects - but they are all the same species, the Melbourne trapdoor, Stanwellia sp. But are small gravel stones ‘rocks’? I am not sure that they ‘carry’ them. I know they move them. I have photos of the burrows and of the spiders, but not of them moving the ‘rocks’.
This is the Staff Report in question: Can spiders carry rocks?
And “carry” involves supporting the weight of the object. So pushing or rolling a rock around is not “carrying” it. And notice that Doug did say that spiders can push rocks to build burrows.
Thanks for the link, DSYoungEsq. Much appreciated. All makes perfect sense to me. The egg sacs which wolf spiders carry around do look like rocks. But even better is the pellet spider. I’ll leave the description to the expert on them, Barbara York Main, from her book “Spiders”:
“A common South Australian spider, Stanwellia nebulosa or the pellet spider builds an elaborate variation of the sock. … Only the lower part of this spider’s burrow is lined with silk. About half way up the lining forms a loose, upstanding collar to one side of which is attached the neck end of a pear-shaped pebble. When the collar is open, the pebble fits into a pocket in the soil wall of the nest. If disturbed from above the spider is able to tug on the collar from below and draw it closed, meanwhile pulling the pebble down on top of it and thus blocking the burrow. The pebble, being pear-shaped is heavier at one end, thus when the spider chooses to push the collar open again, the counterweighted pebble drops neatly back into its socket. When I first observed these ingenious nests I marvelled at the symmetry of the pebbles. They were all perfect pear shapes but I could never find any similarly shaped pebbles on the ground! Where did the spiders get them? Then I realised that the spiders made the pebbles or pellets by combining silk and saliva into mud which they then carefully moulded into shape. Also the little pocket in the wall of the burrow was scooped out and the walls packed down until the pebble made a perfect but loose fit.”
I’m afraid Doug may have been missing the point in the staff column in question. He’s assuming the questioner is referring to a spider supporting a rock completely off the ground rather than pushing it. But there is nothing in the question about such a definition of “carry.”
As Lynne and others have pointed out, spiders certainly do move small stones by pushing or rolling. There are 3 possible ways (2 common, one quite rare) for spiders to “carry” any object in the sense of supporting it completely off the ground.
One is to attach it with silk to the spinnerets, as wolf spiders do their egg sac. A mother wolf spider deprived of her egg sac will often attach and carry in this way a foreign object of similar size and shape. I imagine this does sometimes extend to carrying small lightweight pebbles.
The second way is to carry it in their chelicerae. As Doug points out, this probably wouldn’t work with any sort of rock or pebble.
The third, rare way is to support an object over the back (much in the way a pack horse, mule or camel would carry their burden). Doug (being an entomologist, not an arachnologist) may not have known there are any spiders that do this. This behavior, found in Aphantochilus rogersi (itself an excellent ant mimic) walks about carring over its own body the corpse of an ant it has fed on, thus being almost literally a “wolf in sheep’s clothing.” Yes, really, I’m not fooling! No spider is known to carry rocks in this manner, but I wouldn’t go so far as to say it was impossible…
Sorry, I agree with Doug. “Carry” means lift, not just move. The question wasn’t about seeing spiders push rocks around, it was about carrying.
Am I the only one who is thinking of a certain scene from MAS*H??? 
“I will not carry a gun, Frank. When I got thrown into this war I had a clear understanding with the Pentagon: no guns. I’ll carry your books, I’ll carry a torch, I’ll carry a tune, I’ll carry on, carry over, carry forward, Cary Grant, cash and carry, carry me back to Old Virginia, I’ll even ‘hari-kari’ if you show me how, but I will not carry a gun!”
Hawkeye rules.