Slime Molds at the Celery Farm

Slime molds are fascinating “creatures”. Not plants, no chlorophyll; not fungi, although they reproduce via spores. Animals? Possibly, since they are mobile. There just isn’t complete agreement about what they are. They are often described as amoeboid. Taxonomy arguments aside, what are they like?

So. A slime mold individual is a single cell ranging in size from microscopic (maybe 0.005 mm) to nearly 0.5 mm. You have to be VERY observant to see them. They feed on bacteria and protozoa, usually on damp wood. That part isn’t so interesting, but when they are short of food, or ready to reproduce, or at some subtle environmental signal, they aggreate to feed collectively. The aggregates, the plasmodia, are bigger and what we notice, along with the reproductive structures they form. Plasmodia can be a millimeter across or range along rotting logs for several feet. Some are lovely, some are ugly, and some may verge on “unappetizing”. They can be spherical, blobby, or dendritic like frost on a window, and may move as a whole or extend themselves to find food, mostly bacteria. They can solve mazes and may form optimized networks to navigate, acting like analog computers without nerves or brains. They are truly remarkable, as are their reproductive strategies.

Some aggregate and sacrifice themselves to form stalks of spores (sporangia); there are a couple of examples in this Bob Kane photo album PDF. Others gather and cocoon themselves in a spherical shell, maybe orange, grey, or pink, to produce their spores. If we crush one early in development we will find colored ooze (like Lycogala epidendrum—Wolf’s Milk), but left alone they change color, perhaps red to grey, and finally crack open to release the powdery mature spores. These transformations will happen quickly, and late-coming observers may only find the remaining debris where nothing was found there only a day before. Bigger aggregates moving and feeding are like the yellow Fuligo septica, Dog Vomit, last for quite a while, but when it’s time to make spores the reproductive structures are ephemeral.

A magnifier is cheaper than binoculars, and slime molds are on wet wood everywhere, so get out and get down. Many of us will have trouble getting up again, but it’s worth it.