With the rains and heat of summer come the vast array of slime molds (also known as dog-vomit fungi) appearing in mulch. They appear in several sizes and colors with no definite shape. The mold may change on a daily basis from a bright yellow netting, to a tan powder, to a dark brown dried blob.
Slime molds get their nutrients from dead organic matter, including mulch. Although slime molds may grow on plants, they do not harm them. Slime molds will eventually disappear on their own. If you want to speed this process, rake the mulch to promote air drying.
For additional information regarding theses molds, try the following web sites: