This technique works fine whether the spider’s on the floor or on the wall as long as the surface is reasonably smooth. If the spider’s on a wall then remember to have your piece of cardboard within easy reach, because the plastic container’s not going to stay in place while you walk back to get the cardboard.
You have to be pretty quick to get a container over the top of a spider like a Huntsman. I always use a transparent container so I can see what’s going on. Take-away food containers are great for this, but remember to eat all the food out of them first.
Pro tip: the trick to getting the container really, really close over the spider is to work in extreme slow motion. Spiders see quick movements easily, but extremely slow movements not so much. With a big spider I will therefore move the container up to it very, very slowly and only when the spider is almost enclosed do I plonk the container over it.
Slide a sheet of stiff cardboard under the container, being careful to allow the spider to climb over the cardboard, and keeping the container held against the wall/floor. This is when you appreciate being able to see through the transparent container
With the cardboard held under the container you can lift it away
I prefer to flip it around so the the spider is sitting inside the container instead of standing on the cardboard
Once I’ve caught a spider and let it free outside I like to keep the container and cardboard handy for the next time.
Because there’s always a next time!