On a recent trip to a range of rock formations near the Sierra Nevada known as the Alabama Hills, I spotted a white-lined sphinx moth, Hyles lineata, pollinating outside of a gas station during the late afternoon. The moth’s size has earned it the common name of the hummingbird moth, making it an easy winged insect to spot, and its habitat range is wide. This moth is not a picky eater, and while it contributes to pollinating many different plants, its caterpillars are known to damage crops. The moths need the plants, the plants need the moths, and we desperately need them both.
The relationship between pollinating insects and plants is profound, speaking to a level of coexistence and coevolution that is truly inspiring. I usually think of moths as nocturnal pollinators and rarely catch a glimpse of them while feeding, so seeing this moth reminded me of their importance within ecosystems.
Moths are usually seen on flowers that provide landing platforms and with nectar deeply hidden. Soon after the white-lined sphinx sighting, we found ourselves amongst the iconic Joshua trees. The yucca is an example of plants totally dependent on the pollination of specific moth species. The female yucca moth (Lepidoptera, Prodoxidae) forms pollen balls using her mouthparts and then stuffs the ball into the stigmas of the various flowers she visits. Without this very intentional routine the yucca flower would not develop fruit or seed pods. During this process the female moth will lay an egg into the flower’s chamber which protects the egg while it develops. At the arrival of the newborn caterpillars the yucca will have developed seeds, which in turn become the caterpillars’ food source.
While watching the moth I contemplated the diversity of plants and pollinators, and considered how intertwined their relationships are. The much smaller and unassuming yucca moth uses an irregular mouthpiece to pollinate the yucca, making it a critical member of the desert ecosystem. This relationship is no accident. Unlike other pollinators that unintentionally pollinate the plants they feed from, the yucca moth caterpillars need the yucca to survive – an intentional relationship that has evolved to benefit both the plant and the insect over millions of years. The yucca’s flowers provide a source of food for many different insects, ground squirrels, and birds, each owing their existence to a tiny responsive moth.
Due to rising temperatures and water scarcity in the desert the number of Joshua tree seedlings that survive and mature is decreasing, diminishing the diversity of this unique ecosystem. Joshua trees are migrating in response to their habitat warming, dropping their seeds further northward. Only time will tell whether the yucca moth is up for the move. The rest of the desert ecosystem depends on it.