Ok, this is odd. Everywhere I clicked on the forge by the mender, it said the forest spider was already in. And I could not pick up the tongs. What I had to do was jump up ON the forge, mender on my left and arond the top on the right I could see the tongs. Then click on the right top area to get the menu options to put the forest spider in the forge. Holding it nearby does nothing and only gives you the option to put the spider all the way in. Then the tongs were highlightable to me. Then I could use them to pick out the spider and progress in the quest.
I dunno, seems kinda bugged. It CAN be done but you have to do the right combination of stuff.