Featured Creature: Yucca

What plant can also be used as a soap,
but without a certain insect, simply could not cope? 

Yucca!

On a dreary, gray day at school, as I hurried from one academic building to another, I spotted a patch of spiky green shrubs, sticking out like a sore thumb. These plants gave me pause because though they were a familiar sight, I had last seen them in the high desert of Mancos, Colorado, a very different setting than my New England college campus, some 3,000 miles away. How did they get here? I wondered, and how are they thriving in an environment so different from the one I had last seen them in? 

There are about 30 species of yucca, most of which are native to North and Central America. The yucca that I recognized on my campus walk was soapweed yucca, also known as great plains yucca. Soapweed yucca is a shrub with narrow leaves, almost knife-like in their sharpness, which can grow up to 3 feet tall. Soapweed yucca grows in the dry, rocky soils of short grass prairies and desert grasslands and thrives in more arid biomes. Still, it can be found across the United States; the yucca’s thick, rhizomatous roots (horizontal underground stems that send out both shoots and roots) allow the plant to thrive in many environments with different soils, including sand. It is a hardy plant, and can tolerate cold and moderate wetness, hence its ability to survive on my college campus in the Northeastern United States.

The shrub received its name, soapweed, due to the saponin contained in its roots. Saponin is a naturally occurring substance in plants that foams upon contact with water, creating a natural soap, which is something that I wish I had known as I camped feet away from the yucca in Colorado. In addition to its cleansing properties, the saponin has a strong bitter taste, and is used by plants, such as the yucca, as a deterrent against hungry insects and animals alike. For humans however, these characteristics make it an attractive partner. These saponin can be turned into sudsy cleansing soap. This process has been used by indigenous peoples for hundreds of years, and is modeled in the video below.

The flower and root of the yucca plant have been used as a nutritional, and tasty snack for centuries. As we learned earlier, the roots and flowers of yucca contain saponin, which, while offering medicinal and hygiene benefits, can be toxic or harmful if not properly prepared for consumption. When consumed, the saponin has a bitter taste, and can cause a burning sensation in the throat. However, if properly prepared, the yucca flower and root can be used in a variety of different recipes. The following video shows the proper way to prepare, and eat, yucca flowers. 

In addition to eating the flowers of the yucca plant, the root holds incredible nutritional and medicinal benefit. Roots were used in a salve for sores and rubbed on the body to treat skin diseases. The sword shaped leaves of the yucca plant could also be split into long strips to be weaved into useful cords. Due to the strong fibers contained in the leaves, yucca could be stripped into thread to fashion baskets, fishing nets, and clothing. 

The Yucca Moth 

During the spring months, from the center of mature soapweed yucca blooms a beautiful stalk of cream colored flowers. At the same time as the yucca flower blooms, an insect called the yucca moth emerges from its cocoon. The yucca moth is small, and white in color, closely resembling a petal of the yucca flower, which allows the insect to blend in with the blossoms. There is a powerful symbiotic relationship between the yucca plant, and the yucca moth, meaning that two organisms have a long term, mutually beneficial biological relationship. 

After breaking out of their cocoons, the male and female yucca moths find their way to the blossoms of the yucca flower, where they mate. The female yucca moth then gathers pollen from the yucca, flying to different plants which ensures the cross pollination of the plant.  She shapes the pollen into a large lump, which she holds underneath her chin as she travels, searching for the proper flower to lay her eggs. This ball of pollen can reach up to three times the size of her head! Once located, she lays her eggs in the ovary of the yucca’s flower. She then deposits her collection of pollen onto the stigma of the flower, pollinating the yucca, which will now produce fruit and seeds for her larvae to feed off of. The larvae mature before they can
consume all of the yucca’s viable seeds, allowing
the yucca to continue to reproduce. 

Leaving her larvae, the eggs grow for a few weeks on their own. Once they reach the right size, the larvae drops from the yucca flowers to the ground, where it burrows underground and forms its cocoon. The lifespan of a yucca moth is only about a year, and the majority of that time is spent in the pupal, or cocoon stage, under the earth. Once an adult moth has mated, it marks the end of their brief life as adult moths. Once underground, the insect will remain in this cocoon in a dormant state until next spring, when the yucca flower begins to blossom, and the cycle continues. 

The yucca moth is the primary pollinator of yucca plants, and its larvae depend on yucca seeds as a key food source. While the relationship is highly specialized, some yucca species can self-pollinate to a limited extent, and other insects, such as bees, may occasionally contribute to pollination. Without one, the other simply would certainly struggle to survive as they do today. Although yucca moths are native to the southwest areas of North America, as yuccas have expanded across the country, some species of yucca moths have also spread, although their distribution remains closely tied to the presence of their specific yucca host plants.

Perhaps the soapweed yucca that I stumbled across in New England autumn already had cocoons of yucca moths, lying hidden and dormant beneath my feet. 

Sources and Further Reading:

• ADAM’S NEEDLE Yucca filamentosa L., USDA
• Agavaceae—Century-plant family, Yucca L., Robert R. Alexander, Floyd W. Pond, and Jane E. Rodgers
• Yucca Moths (Tegeticula sp.), Beatriz Moisset
• Soapweed Yucca (Yucca glauca) Charlie McDonald