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Broadcast on September 23, 2010
By Megan Wilde
Most animals wouldn’t dare eat the sprawling gray-green vines of a buffalo gourd, even if it were the only plant growing in a pasture. And for good reason. Though the gourds look like small, round watermelons, they taste horribly bitter and smell even worse.
That’s how they earned the nickname “stink gourd” and the scientific name Cucurbita foetidissima—“most fetid.” But to some beetles and bees, this Chihuahuan Desert native is the center of the universe. Even desert-dwelling humans have found them useful. Why are these gourds so stinky? And what does this malodorous plant have to offer?
Buffalo gourds reek because of cucurbitacins, one of the most bitter ingredients in the plant world’s pantry. These potent natural pesticides are found in all wild gourds, as well as in their tamer relatives—cucumbers, squash, and melons—though in much smaller amounts. Cucurbitacins are not only bitter, but toxic. Feasting on wild gourds can kill sheep and cattle. For people, the price of ingesting cucurbitacin can range from gagging or passing out, to several days of diarrhea and stomach cramps.
But to one group of beetles—the Luperini—nothing tastes better than cucurbitacin. Corn rootworms and cucumber beetles have evolved to not only safely eat cucurbitacins, but to gorge on them. In fact, the beetles and buffalo gourds actually help each other out.
Once established in a perennial stand of buffalo gourds, the beetles prefer gorging on cucurbitacin-rich seedlings. Meanwhile, the nearby adult plants are largely spared. In this way, the beetles reduce competition among young and old plants for scarce resources like water, keeping the buffalo gourd stand at a healthy population density. The beetles benefit by filling themselves with foul-tasting cucurbitacins, an excellent deterrent to birds and other predators.
Luperini beetles aren’t the only insects that ignore buffalo gourds’ rank odor. To squash bees, no other plant smells so sweet. These solitary bees’ entire lives revolve around wild gourds. Their mutually exclusive and beneficial relationship is described in Gary Nabhan’s book Gathering the Desert.
At night, male squash bees sleep cupped inside buffalo gourd’s pale blossoms, while females sleep in tiny burrows under the vines. Then, early in the morning, when the pre-dawn light is just bright enough for squash bees to see the gourd’s highly reflective flowers, the bees start their work day collecting gourd pollen. When they’re not working, squash bees remain inside gourd blossoms, grooming themselves or just hugging the flowers’ styles. The gourds, in turn, exclude other pollinators by shutting their blossoms . The flowers are also perfectly conformed to fit squash bee bodies, and inside flowers, the sweet nectar can only be reached by squash bee-sized tongues.
Even humans have learned to take the bitter with the sweet. For at least 9,000 years, inhabitants of the southwestern U.S. and northern Mexico have found ways to use buffalo gourds, their triangular leaves, and their giant tuberous roots. The dried gourd shells make excellent containers. The cucurbitacin-free seeds can be roasted and eaten. The green fruits and roots contain soapy substances called saponins, and are still used as a laundry detergent in some places. Native Americans deployed a powdered gourd-root tea as a laxative and to speed up childbirth. Pharmacological studies have found cucurbitacins can even hinder the growth of certain cancerous tumors. And researchers have also looked to these ubiquitous desert plants as a potential biofuel source.
Ironically, the most fetid part of buffalo gourds has proven to be quite valuable to humans. Scientists have found ways to exploit the cucurbitacins in wild gourds as a foil for cucumber beetles and corn rootworms, formidable agricultural pests. When wild gourds grow alongside commercial crops, the pesky beetles will gravitate to the wild gourds instead of valuable squash, cucumbers, melons and corn. Scientists have also concocted a pesticide from buffalo-gourd cucurbitacins. This poison is less harmful to beneficial insects and groundwater than the chemical arsenal previously used to protect corn crops.
So, should you ever find yourself repelled by the stench or taste of a buffalo gourd, remember: some Chihuahuan Desert inhabitants cherish these bitter fruits.
Have a question or comment about this episode? Contact Nature Notes Coordinator Megan Wilde at mwilde [at] cdri [dot] org. Or discuss this episode on Nature Notes’ Facebook page. This episode originally aired on September 23, 2010.
References & Resources for Educators
- “Gathering the desert” by Gary Paul Nabhan (University of Arizona Press, 1985)
- “Buffalo Gourd” by J. Philip Dering, from Texas Beyond History: Ethnobotany of the Lower Pecos Canyonlands
- “The Bitter End” by Janet Raloff (Science News, July 10, 1999)