Yuccas and yucca moths have a mutualistic relationship. The yucca needs the moth for pollination, and the moth needs yucca seeds as food for its young. So strong is the tie that likely both a yucca and its particular species of pollinator will become extinct if either falters.
Life is not without problems, however. In dry years, yuccas may not be able to produce seeds. This isn't a serious difficulty for the yucca, because it has more years to try for successful reproduction. For the short-lived moths, however, it's a potential disaster—in years with no yucca seeds, all their young would die. How can you guarantee there will be moths around the next year? Simple—mimic the strategies of desert annual plants, wherein only a portion of the seeds germinate each year.
During good years, the mature moth larvae drop from the yucca and
burrow into the ground where they go into dormancy, called diapause. Some will
metamorphose into moths and emerge the following year. Others will remain in diapause
for 2 or more years, hopefully emerging to bountiful yuccas.
Listen to the Audio (mp3 format) as recorded by KTEP, Public Radio for the Southwest.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.
Half of the partnership. Torrey Yucca (Yucca torreyi) blossoms, University of Texas at El Paso campus. Photograph by A. H. Harris, 19 March 2001.
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Schrock, J. R., and G. Leisman. 1987. Wildflower in the Spotlight: Yucca or Soapweed, Yucca glauca. Kansas Wildflower Society Newsletter, 9(1):5-11.
Wayne's Word. Text and photographs of yuccas and yucca moths.