About 6 weeks ago, I saw something I'd never seen before: a foamy, tan colored blob about 5" long on the hardwood mulch in one of the garden beds. Since then, there's been more instances, some more yellow, some whiter, some browner.
Apparently, this is slime mold, sometimes referred to as "dog vomit" fungus. It feeds on bacteria in the mulch, and typically first occurs in very rainy weather or if an area is heavily irrigated. The foamy mass eventually goes away, especially if the weather turns hot and dry, and doesn't hurt anything. But if it is too unsightly for you, just scoop up the mulch with the mold on top, and discard in the trash.