Montana Public Radio

Bug Bytes: Yucca Moth

Jun 12, 2020

In Montana, the small soapweed yucca is a plant native to the central and eastern part of the state, east of the Continental Divide. But thanks to its showy, fragrant stalks of beautiful white flowers, it's a popular addition to gardens west of the divide too.

But there’s one big difference between yuccas growing within their native range versus the non-native transplants …the plant will only produce its big seedpods in its native range.

Is it because of differences in climate, soils, or maybe the amount of rain? It all boils down to the presence of one, very specific insect – the yucca moth – the only insect capable of successfully pollinating the plant.

A yucca moth.Photo by Ann Cooper. Glenn got permission to use this photo from Ann at https://bugguide.net/node/view/119525. Copyright ©2007 Ann Cooper
Credit Courtesy of Ann Cooper / https://bugguide.net/node/view/119525 ©2007 Ann Cooper

The yucca moth does not have a long tongue (or proboscis) to feed on flower nectar. In fact, it does not feed at all during its short life. Instead, the moth has specialized tentacles around its mouth that serve a unique function.

After mating, the female gathers pollen from a yucca flower and stores it in a ball under her chin. She’ll then visit a flower of a different plant, deposit several eggs, and purposefully remove pollen from her chin, placing it on the plant’s stigma.

Successfully pollinated, the flower is now able to produce a fruit (or seedpod) with so many seeds that there’s plenty for the yucca moth’s developing caterpillars to eat as well as provide for the next generation of plants.

This incredible species-specific relationship is called an obligate mutualistic relationship. In other words, the yucca plant and the yucca moth’s lives are so interdependent that one cannot live without the other.

Next year’s generation of moths won’t simply emerge when the weather becomes warm enough, they time their emergence with the blooming of the yucca plant so they can start this amazing cycle all over again.