They look like visitors from another world.
Some sprout short stalks capped with salmon-hued baubles; others collect in foamy-looking masses or sprawl in rippling yellow webs. Despite their otherworldly looks, these colorful globs are indeed Earthlings. They’re slime molds, a hodgepodge of different species across multiple groups, some only distantly related. And despite their name, these blobby creatures are not related to mold but are among the large group of mostly single-celled organisms known as Amoebozoa.
Slime molds flourish in damp environments around the world, like the nooks of decomposing logs on forest floors. In your own backyard, they may emerge among the chips of mulch.
Mycologist Marie Trest of the University of Wisconsin-Madison fondly recalls a particularly wet summer when patches of slime mold speckled her yard. When she and her daughter sprayed the patches with a hose, spore-filled sacs burst, propagating the next generation. “We were just growing slime molds in the garden for the whole summer,” Trest says.
The patches in Trest’s yard were “dog vomit” slime mold, one of the plasmodial slime molds. They spend one phase of their lives as blobs searching for microorganisms to eat and another growing stationary spore structures in myriad hues and shapes. The group includes one of the stars of the slime mold world, the vivid yellow Physarum polycephalum. Creeping along on gooey tendrils, the species has intrigued scientists with its rudimentary “intelligence”: Though it has no brain, it can identify the shortest path through a maze and remember food locations by imprinting them in the tubes that make up its body.
Despite scientists’ research, many mysteries remain about slime molds. Why such brilliant colors? Why so many different shapes? How many species not yet discovered? “It’s painful how much we don’t know,” says one of Trest’s university colleagues, mycologist Anne Pringle.
“Much of Earth’s biodiversity goes unnoticed, unrecorded, unstudied,” she says. Slime molds are a magnificent reminder of those untold riches, waiting to be found.
For these images, photographer Andy Sands magnified the slime molds many times; most of them are only hundredths of an inch tall. Sands also used a process called focus stacking, in which multiple similar photos with different focal points are blended to achieve a more profound depth of field. Photographs via Nature Picture Library.
This story appears in the May 2023 issue of National Geographic magazine.