Well... It's a little to far away and unfocused to see what they are.
Are they perfectly spherical? If bumpy, then they could be perlite from the potting mix. They float, so when there is heavy rain, they tend to all float up and then cling to the edge of the pot while the water drains away. If there is a heavy downpour, all those perlite will just wash away when the water overflows over the rim.
Sometimes, slime mold will form spherical fruiting bodies (like mushrooms) of varying colors including white, but I'm leaning towards perlite.
BTW spiders are a good friend. I prefer one spider to several dozen pest bugs.