I remember these little critters from an old Forgotten Realms Montrous Compendium, I just refound them on the enworld site converted for 3rd edition. These little guys will come In handy In the jungles on the Isle of Dread. Here's the link.
http://enworld.org/cc/converted/view_c.php?creatureID=509
I love Monkey Spiders, and actually did use them as a swarm in "There Is No Honour" for one PC. He spilled the crate in one of the bars in the Azure District, and hundreds of monkies poured onto a poor Half-Orc pirate.
~ Bryon ~