Not Only Rabbits Appreciate the Rubber Rabbitbrush
By R. Gary Raham:
In the fall, at the west end of my house, when the flowers of other plants are gone or fading fast, a rabbitbrush shows off by bursting with fragrant, golden blooms. A Checkerspot or Painted Lady butterfly might dip here and there like a customer at an all-you-can-eat buffet. Bees buzz, sipping nectar and transporting pollen. Sparrows skitter and chirp beneath the canopy of blooms and gnarled branches. And yes, a rabbit may shift position, deciding how much of a threat I pose. The rabbitbrush, a hardy perennial shrub in the arid west, not only serves the role of attractive host for a variety of wildlife, it offers enticements that lure humans into exploring its complex biochemistry as well.
Native Americans had many uses for this shrub. According to Kathleen Keeler, “A Wandering Botanist,” (http://khkeeler.blogspot.com/2017/09/plant-story-rubber-rabbitbrush-painting.html) the Navajo used it in cleansing ceremonies. The Cheyenne consumed it as a cold remedy. The Hopi wove the bark into baskets. The Hopi and Navajo turned flowers and stems into deep yellow and olive green dyes. Some Native Americans apparently brewed tea from its leaves and pulverized its wood and bark to make chewing gum. And the plant burns well—one reason to keep it at a safe distance from the house.
The stems of rabbitbrush exude an odor that many people identify with heavy oil or rubber—a reason, perhaps, for its scientific name, Ericameria nauseosa—“Smelly plant with heath-like leaves.” he oily smells contrast with the sweeter odor produced by the flowers.
Beetles, apparently, don’t mind the oily smells. At various times I’ve seen these insects engage in orgies of eating and/or copulation on the plant. One season at Soapstone Prairie Natural Area just north of Fort Collins, for example, the rabbitbrushes along the trail to the picnic tables writhed with the orange and black bodies of soldier beetles looking for the perfect union. Normal people might avert their eyes, but naturalists thrive on such resplendent passion, even in the arthropod orders.
On my personal, west-side-of-the-house rabbitbrush, the metallic green larvae of the beetle, Trirhabda nitidicollis, on one occasion decorated leaves and stems like tiny Christmas ornaments. They practiced an orgy of eating that can, but not usually, denude the plant. Predatory stinkbugs and lady beetles usually keep the beetles’ numbers in check. I learned to identify the mating and egg-laying adult forms of these metallic herbivores: a not quite-so-flashy beetle who sports pale, greenish-cream elytra (the hard outer wings) accented with black stripes. After the glittering larvae have eaten their fill, they move to the soil and pupate to complete their life cycle.
During World War II, human military machines needed rubber to function. A warplane, I learned, required a half-ton of rubber parts. Sherman tanks needed a ton of rubber and a battleship required 75 tons. Even footsoldiers needed 32 pounds of rubber for footwear, clothing, and equipment. When the Japanese commandeered most of the Southeast Asian rubber tree plantations, Western militaries frantically sought to conserve rubber and look for other sources. The rabbitbrush produces chrysil, a natural rubber that showed potential, but was expensive to process. Eventually, technologists created a reasonably cheap synthetic rubber, and Southeast Asian sources returned. Researchers abandoned work with the rabbitbrush.
A scientist with the College of Agricultural Biotechnology and Natural Resources at the University of Nevada now thinks the rabbitbrush’s time has come again, as a viable source of natural rubber. Dr. David Shintani says the rabbitbrush is also rich in oleoresin, a potential precursor of biodiesel fuel and adhesives—not to mention dyes. Cellulosic residues from the plants might also be used as a source of biomass to generate electricity. (See https://www.unr.edu/cabnr/about-cabnr/cabnr-newsletter/rabbitbrush-rubber)
Sarah Malaby with the US Forest Service also notes that, “Compounds in rubber rabbitbrush are being evaluated for nematocides (worm killers), anti-malarial properties, and insect repellents.”
If it became commercially valuable, according to Dr. Shintani, rabbitbrush grows so easily in dry mountain valleys and plains that it wouldn’t displace other crops. It grows in a wide range of soils and actually produces more rubber when soils are poor. Shintani has been studying rabbitbrush for ten years and says there’s still a lot to do, but he has high hopes that rabbitbrush will become a fantastic chemical resource.
Let’s hope that rabbitbrush can fulfill this kind of potential for human uses without losing its role as a shelter, nectary, food source, trysting place, soil stabilizer, and billboard for the color gold. The rabbitbrush has lots of friends and companions in arid places. And, the rabbitbrush provides better stories than Netflix throughout the summer, and during brisk autumn days under quintessentially blue western skies.
Gary Raham is a nature writer and illustrator. He is the author of: The Restless Earth: Fossils, The Dinosaurs’ Last Seashore, A Singular Prophecy, and other titles of science fact and science fiction. Download a free sample of Confessions of a Time Traveler at http://www.biostration.com/books/CTTindex.html.