The Elegance of Slime Molds
Amorphous and creepy, these eccentric life forms intrigue artists and scientists alike.
By Susan Kaneko Binkley
Slime molds are creatures in need of a proper introduction. When they don’t receive one, their appearance causes fear and revulsion–even mass hysteria.
Gardeners who happen across the slime mold Fuligo septica seldom know what to make of it. Often seen growing on lawns and mulches, F. septica is perfectly harmless–though dogs may disagree. The mold’s scrambled-egg appearance has been misconstrued as a sign of canine malady, often sending a healthy pet to the veterinarian–and resulting in the common name dog-vomit slime mold.
It takes a little more imagination to see why in 1973 folks in Dallas, Texas, became so alarmed by a large outbreak of strange growths on their lawns. When one of the big yellow blobs appeared on a telephone pole and began to spread, firefighters tried to subdue it with hoses; but the mass multiplied and moved–up the pole. Many residents feared a dangerous alien life form was attacking the city. Fortunately, a local university scientist identified the oozing slime as harmless F. septica.
Rarely are slime molds this large and ghastly. Most are very tiny and inconspicuous–less than an inch in size–and strikingly beautiful in form as well as color when observed close-up, as James Sogaard’s photographs show.
Scientists once thought slime molds to be a kind of fungus. Because some species creep en blob from one place to another, a 19th-century mycologist referred to slime molds as mycetozoans, or fungus animals.
Now taxonomists know that slime molds are not fungal, animal, plant, or bacterial, but are an independent group of organisms. Structurally, the plasmodium, one of the life stages large enough to be seen, is nothing more than a gob of protoplasm held together by a cell membrane.
Many slime molds thrive in forests within and on moist bark, rotting logs, leaf litter, dung, and soil. There are 64 species that have been identified in Minnesota. Of the approximately 1,070 species known to science, many are found worldwide.
Moving at speeds up to 1 millimeter per hour (with an exceptional few moving as fast as 2 centimeters per minute), slime molds are slow-motion predators, usually locating bacteria or fungi to consume. They scavenge decaying organic material as well. As slime molds flow over and engulf their food, they ingest it. If an item turns out to be inedible, they eject it.
Slime molds apparently use chemical signals given off by food sources to sense which way to move. Researchers in Japan recently proved that Physarum polycephalum will consistently work out the shortest path between two piles of nutrients in a maze.
Slime molds begin life as microscopic spores. When conditions are right, the spore opens and releases a single-celled organism called an amoeba. What happens next depends on which of two groups the slime molds belong to.
Within the group of acellular slime molds (Myxomycota), flagellated, swimming swarms of amoebas fuse together to form a plasmodium, a giant single cell with thousands of nuclei that divide and grow and do everything as one.
Members of the other group (Dictyosteliomycota and Acrasiomycota) are cellular slime molds. Dictyosteliomycota cruise along as single, unattached amoebas for most of their lives until a chemical signals that the single life is over. Then, one by one, up to 100,000 amoebas in an area find each other and fuse into a single multicelled pseudoplasmodium.
In the final stage of both groups–triggered by adverse conditions such as lack of food, too much heat, flooding, or wrong pH–fruiting bodies develop and release the spores of the next generation.
With such a spectacular life cycle, much of it visible to the naked eye, slime molds have become popular lab subjects. Scientists and mathematicians use them to study an astonishing array of areas in medicine, developmental biology, computer modeling and gaming, and genetics. Because of the importance of Dictyostelium discoideum to so many research fields, the National Institutes of Health selected it as one of its model organisms for gene sequencing.
Long before they attracted the notice of the scientific community, slime molds had beguiled nature lovers with their bizarre forms and colors. According to a story in the March 2001 Smithsonian, the 15th-century Flemish artist Hieronymus Bosch painted 22 species of slime molds in his fantastic, otherworldly triptych The Garden of Earthly Delights. For more than a century, naturalists have cataloged slime molds in drawings, herbariums, and collections of cultured specimens. In Meiji-era (1868—1912) Japan, botanist Minakata Kusagusu was so determined to grow slime molds in his container garden that he trained cats to keep slime-mold-eating slugs out of his extensive collection.
Today, slime molds are the subject of international congresses, forays and expeditions, and web sites–all for science professionals as well as hobbyists. Slime molds share characteristics with both animals and plants and are included in herbarium collections worldwide. University of Minnesota Herbarium curator David McLaughlin oversees a mounted collection of the 64 species of slime molds that have been found in Minnesota.
Small as they are, slime molds with their unusual forms and colors have managed to capture people’s imaginations, as reflected in many common names: wolf’s milk, yellow tinder blossom, Japanese lantern, bubble gum, spaghetti, red raspberry, chocolate tube, and tapioca. Many names suggest edibles, and, indeed, Indians in one area of Mexico scramble and fry Fuligo septica like eggs. They call their tidbit caca de luna or "moon ca-ca." Somehow, the odd name befits a quirky little beast that brings out the quirkiest in us.
Susan Kaneko Binkley, art director of the Volunteer, is fascinated by nature’s oddities. James Sogaard, free-lance photographer, has been in slow pursuit of slime molds for more than 10 years.
