You have to match Cropsies next to a spider to make it move.
You’ll usually have to break some spider webs first, which you can do by matching with the Cropsie in the web. When you can finally make a match next to the spider, it will try to jump to a new nesting spot (this will look like a dense white web).
If there are no other nesting spots on the board, the spider will be collected. You can use a shovel or tractor booster to help you clear spider webs.