Jennifer Schultz Nelson
Extension Educator, Horticulture
Sometimes gardens are not for the squeamish. Recently I was puttering around outside and noticed what looked like vomit in several places all over the mulch in my garden. After the initial "Ewww!" reaction, I got curious. I figured it was some sort of slime mold, but wanted to know more.
I identified it as Tapioca Slime, Brefeldia maxima. Besides a striking resemblance to vomit, its other claim to fame is being one of the largest slime molds. It really does look like tapioca in its early stages–shiny, white and lumpy. As it matures it looks more like a cushion and takes on a pinkish hue that eventually darkens to black. Its favorite habitat is dead wood and leaf litter, so my garden filled with partially composted wood mulch is ideal for Tapioca Slime.
When you get past the gross factor, slime molds really are fascinating. Technically, they aren't fungi at all, though they are typically lumped in with fungi in identification books, and mycologists study them along with fungi.
Slime molds have several life stages, each very different from the other. The only stage that is really "slimy" is the plasmodium stage, where the slime mold is mobile, much like the "blob" of science fiction movies.
As a plasmodium, a thin cell membrane encases the protoplasm, or cell contents. The slime mold moves via "protoplasmic streaming" a systematic expansion and contraction of the cell membrane. They are slow movers, most moving at most a millimeter per hour. But there are a few speed demons that move up to two centimeters per hour.
Slime molds move in search of food. Generally they feast on bacteria, fungi, and decaying organic matter, such as the wood mulch in my yard. Japanese researchers found the species Physarum polycephalum always took the shortest route when they placed it in a maze with two possible routes to food sources. They hypothesize that this movement is in response to chemicals given off by the food source.
If you do not want to share your garden with slime molds, the best control is to use a rake to loosen up the mulch and encourage air circulation. Dry mulch is much less likely to support slime molds than damp mulch.