Spider bubbles are introduced at level 26. Their main mission is to destroy spiders. You launch a spider bubbles destructive behaviour by bursting it in a group of three or more bubbles. Then it spits green poisonous slime, that will destroy any spider that gets in the way.
Sometimes it is however better to let the slime destroy a spider, because if you have to choose not to burst a bubble, two spiders will go off-game up into he ceiling.
Spider Bubbles appear in all the same colours as ordinary bubbles appear.
Here is a video that I made for level 28 that gives you an idea what Spider Bubbles is all about. :)