The great love affair of the desert: the joshua tree and its moth.
But there’s a problem here. The joshua tree is critically threatened by climate change. The night time lows are higher than they have been, and daytime highs are getting higher, drying out the already dry soil. Scientists estimate that the range of joshua trees within Joshua Tree National Park by the end of the century will be 10% of what that range currently is. Joshua trees are naturally moving northward and upward in elevation: cooler and wetter. But the question is: will the yucca moth migrate with the joshua tree? If it won’t, then what happens?
Excerpt:
We’ll start with the Joshua tree, the Mojave Desert’s most iconic plant. With its spiny fronds and clubbed tufts topped by pungent, waxy flowers twisting towards the desert sky, this desert-adapted shrub has a reputation for otherworldliness. Everyone who passes through the desert remembers the majestic Joshua tree; its namesake has inspired artists, filmmakers and many a sojourner in search of transcendence.
Few travelers, however, wax poetic about its evolutionary partner, the yucca moth. The small, dun bug is initially unassuming, but upon closer inspection, it is an equally extraterrestrial match for the iconic Joshua tree. Instead of a regular mouthpiece, it sports bizarre, tentacle-like fronds, the likes of which are unique among insects—and serve an essential purpose in the desert ecosystem.
Without nectar to attract pollinators, Joshua trees rely solely on this unassuming moth for pollination. Yucca moths use their dexterous jaw appendages to collect pollen from Joshua tree flowers and deposit it on the female parts of each flower as the moth moves between blooms. In turn, the moth lays her eggs with its thin, blade-like ovipositor on the flowers’ seeds.
When they hatch, the yucca moth caterpillars eat the seeds—their only food source—before crawling to the ground to form cocoons. And the cycle begins again.
According to Christopher Smith, a biologist at Willamette University who studies pollinator relationships, the relationship between yucca moths and Joshua trees is unlike anything else in the natural world. He should know: Smith has long studied the diverse relationships between insects and plants in the desert. His previous research focused on cactus longhorn beetles and the spiny plant species they interact with throughout the Sonoran Desert. But nothing, he says, compares to the Joshua tree and the yucca moth.
Most pollinators accidentally assist the plants they pollinate. Bees and birds will brush up against pollen while they are feeding on a flower’s nectar, spreading it from plant to plant as they continue a day’s feast. Not yucca moths: because their caterpillars depend on the continued existence of Joshua trees and their tasty seeds, the yucca moth’s pollination is an active act of survival. Moreover, this partnership has been going on for millions of years.
Joshua trees do more than provide artistic inspiration: they create essential environmental support for the uncompromising desert ecosystem. These hideously beautiful shrubs provide food and shelter for animals in the Mojave scrublands, where resources are notoriously scarce. During the spring, its flowers are one of the only sources of wet food available for insects, ravens, and ground squirrels.
Yet today, their long-lived partnership may be in danger of breaking down, as the Joshua tree’s natural habitat faces new threats.
The unremarkable-looking yucca moth is one half of an evolutionary partnership that dates back millions of years. (Will (Tad) Cole)
