In the 1958 film, “The Blob,” a huge amoeba-like creature from outer space engulfs and kills several people in a small Pennsylvania town before it is eventually destroyed by a local teenager, played by Steve McQueen. The courageous teen kills the blob using a fire extinguisher after he realizes it cannot survive cold.
This “blob” was pure science fiction. Interestingly, blobs exist in our natural world, and they are called slime molds. Fortunately for earthlings, however, they are harmless and subsist on much smaller prey: bacteria, spores and tiny bits of organic matter.
Known to biologists as myxomycetes, slime molds live in damp places, such as on logs, under bark, in leaf litter or on bark mulch. In recent decades, bark mulch has become a popular element of the landscaped yard, so blobs, often brightly colored, are typically found under shrubbery.
Slime molds are strange, interesting and beautiful during parts of their life cycle. They are strange because, when feeding, they act like animals, but in the reproductive phase they behave and look like fungi.
Unlike most animals, plants and fungi, slime molds are cosmopolitan. Many of the roughly 700 species of myxomycetes are found worldwide, wherever plants, their main food, are found. In its adult, feeding phase, a slime mold looks like a glistening mass of mucus, normally ranging from microscopic to Frisbee in size, but occasionally larger—the biggest found measuring 30 square meters.
The mucus mass is called a plasmodium and typically comes in yellow or orange colors, but it may be red, white, buff, maroon or translucent like an egg white. One common species, Fuligo septica, found in Vermont and New Hampshire, looks like a soiled, unappetizing egg white and is one of the few slime molds with a common name: dog vomit slime mold. Despite this disgusting name, this species is fried and eaten in Mexico.
Like a huge amoeba, the plasmodium moves in search of food. Scientists in Japan observed that one species, Physarum polycephalum, can find the shortest distance through a maze to get to oatmeal—an example of an organism without a nervous system being able to process information, which has led to much discussion about what constitutes intelligence.
The plasmodium has protoplasm and multiple nuclei, but no individual cell walls. The whole creature can be considered a single giant cell. Curiously, the nuclei, of which there may be thousands, divide in synchrony, every 8 to 10 hours. This is another slime mold trait that enthralls scientists, especially those who study cell division.
Slime molds cannot be identified to the species level by examining a plasmodium. Rather, scientists must await the remarkable transformation to the spore-bearing phase, since each species has a distinctive way of producing and releasing its spores.
Just what triggers the change from a slimy, crawling, animal-like thing to a spore-bearing, fungus-like one is unknown. A decline in food quality or a shortage of food may be a factor. A change in ambient temperature, or in the pH of its surroundings are among other possibilities. But when the time comes to bear spores, the once moisture-loving blob often climbs up on grass or other vegetation to a drier spot to transform itself. The plasmodium is completely replaced by the spore-bearing structures that together might look like a garden of little sponges, typically one-twelfth to one-fifth of an inch high. Look through a magnifying glass, and you will see a little world of goblets, cups, bowls and what looks like tree-peonies and undersea corals. You will notice all kinds of what might appear to be balls or beans of all colors. Whatever the shape, the spore cases have the same purpose: to propagate more slime molds.
Like many other aspects of slime mold life, the ecological function of these common organisms is not well understood. Some beetle species that eat the fruiting bodies and help disperse the spores are found only on slime molds. Many fungal species consume slime molds, and a few appear to depend entirely on them.
As summer progresses, check the bark mulch, or any decaying logs or forest detritus, and you will likely find a slime mold. In its feeding stage, if you are patient, you can even watch the blob move. Or, if you aren’t inclined to while away a summer day lying in bark mulch, you can mark its location and return a few hours later to note the progress.
Rest assured, though, despite its looks, this creature is not from Mars; it is not out to get you. No need to call Civil Defense or reach for a fire extinguisher.
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