Wendell Smith: slime mold (physarum polycephalum), 2011 (CC)
It is spring in Houston, which means that each day the temperature rises and so does the humidity. The bricks of my house sweat. In my yard the damp air condenses on the leaves of the crepe myrtle tree; a shower falls from the branches with the slightest breeze. The dampness has darkened the flower bed, and from the black mulch has emerged what looks like a pile of snotty scrambled eggs in a shade of shocking, bilious yellow. As if someone sneezed on their way to the front door, but what came out was mustard and marshmallow.
I recognize this curious specimen as the aethalial state of Fuligo septica, more commonly known as “dog vomit slime mold.” Despite its name, it’s not actually a mold—not any type of fungus at all—but rather a myxomycete (pronounced MIX-oh-my-seat), a small, understudied class of creatures that occasionally appear in yards and gardens as strange, Technicolor blobs. Like fungi, myxomycetes begin their lives as spores, but when a myxomycete spore germinates and cracks open, a microscopic amoeba slithers out. The amoeba bends and extends one edge of its cell to pull itself along, occasionally consuming bacteria and yeast and algae, occasionally dividing to clone and multiply itself. If saturated with water, the amoeba can grow a kind of tail that whips around to propel itself; on dry land the tail retracts and disappears. When the amoeba encounters another amoeba with whom it is genetically compatible, the two fuse, joining chromosomes and nuclei, and the newly fused nucleus begins dividing and redividing as the creature oozes along the forest floor, or on the underside of decaying logs, or between damp leaves, hunting its microscopic prey, drawing each morsel inside its gooey plasmodium, growing ever larger, until at the end of its life, it transforms into an aethalia, a “fruiting body” that might be spongelike in some species, or like a hardened calcium deposit in others, or, as with Stemonitis axifera, grows into hundreds of delicate rust-colored stalks. As it transitions into this irreversible state, the normally unicellular myxomycete divides itself into countless spores, which it releases to be carried elsewhere by the wind, and if conditions are favorable, some of them will germinate and the cycle will begin again.
From a taxonomical perspective, the Fuligo septica currently “fruiting” in my front yard belongs to the Physaraceae family, among the order of Physarales, in class Myxogastria, a taxonomic group that contains fewer than a thousand individual species. These creatures exist on every continent and almost everywhere people have looked for them: from Antarctica, where Calomyxa metallica forms iridescent beads, to the Sonoran Desert, where Didymium eremophilum clings to the skeletons of decaying saguaro cacti; from high in the Spanish Pyrenees, where Collaria chionophila fruit in the receding edge of melting snowbanks, to the forests of Singapore, where the aethalia of Arcyria denudata gather on the bark of decaying wood, like tufts of fresh cotton candy.
Although many species are intensely colored—orange, coral pink, or red—others are white or clear. Some take on the color of what they eat: ingesting algae will cause a few slime molds to turn a nauseous green. Physarum polycephalum, which recently made its debut at the Paris Zoo, is a bright, egg yolk yellow, has 720 sexual configurations and a vaguely fruity smell, and appears to be motivated by, among other things, a passionate love of oatmeal.