By RICK BORCHELT
Readers of a certain age will likely remember Steve McQueen’s first starring role in “The Blob” as a teen crusader trying to warn oblivious villagers in bucolic Phoenixville, Pa of impending danger from space. The 1958 movie’s main character isn’t McQueen, though — it’s a supersized intruder that hitched a ride on a meteorite that oozes across Phoenixville and absorbs people, growing larger as it does. Luckily Steve and his friends find the alien’s Achilles’ heel (if said blob actually had a heel) — freezing temperatures — and Earth gets a reprieve from being subsumed by the ever-growing blob by shipping the amorphous menace to an Arctic ice field.
Working in my garden last week brought “The Blob” to mind: A neon-yellow blob of my own had sprung up overnight on the wood chip pile after our last rain. Every time I turned my back, it seemed to grow larger, ending up about a foot long and equally wide by the next day. A few days later, the slimy yellow mess had turned hard and cracked open to expose a black mass inside.
Similar yellow, tan or cream blobs are turning up in gardens, lawns and decaying mulch across the region as the weather turns warm. But we can give a more specific name to this alien-looking creature than simply the blob — it’s the dog vomit slime mold, Fuligo septica.
Dog vomit slime mold is just one of about 60 slime mold species found in Maryland, all members of the puzzling taxonomic class Myxgrastia (sometimes also called Myxomycetes). Red raspberry slime (Tubifera ferruginosa), chocolate tubes slime (Stemonitis splendens), wolf’s milk (Lygogala epidendrum) and tapioca slime (Brefeldia maxima) are some of the fanciful names for other slime molds of Maryland.
Most slime molds are microscopic, but some — the plasmodia slime molds, including dog vomit slime mold — are created when swarming masses of individual cells give up their solo lives for communal life. They coalesce to form one big bag of cytoplasm, which is essentially a single, giant cell. That’s the faux dog vomit I saw creeping over the compost.
When conditions turn unfavorable for this gelatinous mass, the slime mold forms tiny, drought resistant spore capsules that can survive freezing, drying and other environmental indignities. One of the world’s thousand or so species of slime mold survives easily in the Sonoran Desert; others inhabit the high Arctic and the Antarctic (so much for the final solution for “The Blob”!).
Slime molds start their lives as free-living amoebae, single-celled organisms that can change shape and move across their microscopic landscapes by extending and retracting “feet” formed by the flexible cell wall. In response to certain chemical signals, these amoebae come together in a slime mold version of a rave concert to fuse into a gooey sac containing thousands of individual cell nuclei — a mass that behaves like a single organism. This is the life stage that gives the group its common name of slime mold; they are slimy and sticky to the touch.
In this stage, the slime crawls over its habitat, engulfing and devouring microorganisms like bacteria and yeast, algae, and other organic matter in its path. The slime mold flows around potential food, then dissolves the cell wall around its intended dinner and simply absorbs it. These slime molds can move quickly, for a microorganism (more than an inch an hour), although not as fast as the time lapse camera in this BBC video might suggest. Some slime molds can be as large as a square meter; a sizable tapioca slime mold can weigh more than 40 pounds.
When environmental conditions change, in hours or days or weeks, the blob transforms from its creeping phase (the plasmodium) into a spore-producing phase (the sporangium). The blob dries out and either bursts open to release spores directly, or grows spore capsules on top of short stalks that split open. The spores can be carried by the wind or splashed around by rain droplets to new habitats. Some are even transported by slime mold flies and small beetles that specialize in eating slime molds.
Dog vomit slime mold, Fuligo, has a pretty cosmopolitan distribution across temperate regions of the world, as its many vernacular names can attest. In Finland, it’s called paranovi — butter of the familiar spirit — in the old belief that it was used by witches to spoil milk. In Dutch it’s hekensboter (witch’s butter), and in Lavtian ragansviests (witch’s butter) or raganu splaviens (witch’s spit).
Whatever they’re called, slime molds are one of Earth’s most ancient lineages of life. Recent DNA research suggests that the common ancestor of all slime molds may have evolved a billion or more years ago, hundreds of millions of years before what we think of as true plants. All those ancient slime molds would have had to eat would have been algae and bacteria.
There’s no need to worry that the dog vomit slime mold on your garden mulch is going to eat your garden, much less you or your pets or your town. It will quickly run its course and decompose. Hosing it down will only spread it, and replacing your mulch is at best a temporary solution. Let it be, and enjoy the brief color and curiosity that slime mold adds to your yard.
Rick Borchelt is a local naturalist and science writer who writes and teaches about natural history, gardening and the environment. Reach him with questions about this column at rborchelt@gmail.com.
