The Buzz

The Yucca Moth

Drab, nocturnal, a little stout, and quite a bit fuzzy, moths are often overlooked by gardeners. But, while you and the butterflies are cozied up for the night, the moths are winging in the moonlight, and performing some very important pollination services. Because colors and shapes are not as prominent at night, moths aren’t drawn to the same flowers that their diurnal counterparts, the butterflies, are. Instead, moth-pollinated flowers tend to be glowing white, and highly fragrant.

Have you ever slipped out into the garden at night, and caught a whiff of Nicotiana, sultry and sweet in a dewy summer breeze? Nicotiana (flowering tobacco) is moth-pollinated! Some of these night-fragrant plants have highly specialized relationships with their pollinators. One key example is the relationship between (the yucca moth) and Yucca filamentosa (commonly called Adam’s needle, or Spanish bayonet). The relationship between yucca moths and yucca plants has existed for over 40 million years, and is obligatory-- neither could survive without the other. Throughout the winter, yucca moths wait quietly in their cocoons, tucked away underground, sheltered from the cold. On a warm spring evening, they emerge, wriggling free from the earth, and tempted to the heady scent of yucca flowers.

There in the flowers, they meet at last, male and female yucca moth, it is love at first sight! When the romancing is done, the female yucca moth departs, she still has work to do before the dawn. Using two tentacle-like appendages near her mouth, she gently scrapes pollen from the anther of a yucca flower, forming it into a small, sticky ball, which she tucks beneath her head. Off she goes, to a second yucca flower, this time flying to the base, where she carves a small opening to the flower’s ovary. Here, she lays her eggs. Then, she crawls to the front of the flower, and carefully scrapes away a small amount of pollen from her pollen ball, which she packs gently into depressions in the flower’s stigma. At last her job is done: her eggs are deposited, and cross-pollination is ensured for the yucca.

She carefully marks the flower with a pheromone, a chemical signal to other yucca moths that this particular flower has already been visited, and flies into the night. It is important that she leaves this signal-- if too many eggs are deposited, the flower may be aborted altogether. When the eggs hatch, the larvae, cozily sheltered within the yucca’s ovary, eat the developing seeds, but always leave enough for the next generation of yucca plants.

After they’ve had their fill, they burrow out, and drop to the ground, where they will wait in cocoons to begin the cycle again. The pollination of yucca flowers has been studied since the 1870s, and, as far as we know, yucca flowers cannot be pollinated without yucca moths, and yucca caterpillars cannot survive without yucca seeds. So, the next time you see a pale, little moth fluttering by your neighborhood yucca, give thanks to both for helping each other to persist.

By Carson Ellis, MBG horticulturist

Posted by Memphis Botanic Garden at 7:00 AM

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