By Roving Ranger in Borrego
A banner flower year brings many a wonder to the desert floor. Visitors come from far and wide seeking a glimpse of our once-in-a-decade display. Others come to see the spectacle that arises as the flower stalks set their blooms, for one of Mother Nature’s “Flower Children” is about to make its million-insect-march across the flowering dunes.
They start off small and unseen among the greening fields. Eggs laid weeks before by migrating adult moths and butterflies hide under newly sprouted leaves, waiting on time, temperature, and humidity to spill forth their contents. Once released, the small caterpillars quickly gather about the stems, making their way toward the flowering display.
Smooth and green, yellow and black, the Sphinx Moth caterpillars have been waiting patiently for the flowers to bloom. Now with bellies to fill and molts to grow through, they gather in greater and greater numbers, trying to out-compete other “Flower Children” also on the move. Caterpillars of the Painted Lady butterfly, fuzzy black with streaks of copper, rush to consume the late-flowering lupine, while beetles gather to bring down daisies, sunflowers, and a few wayward caterpillars.
But the Sphinx Moth caterpillar (White-lined Sphinx moth-Hyles lineata) out-competes them all! With greater numbers and a staggering growth rate, the Sphinx Moth caterpillar quickly consumes its fill and molts through its many larval stages, out-growing its closest rivals. So numerous are these caterpillars that great migrations of Swainson's Hawks descend upon the Borrego Valley and deserts to the north to feed on this rare outbreak of protein.
History tells us that these caterpillar outbreaks were an important source of food for native peoples all throughout these caterpillars’ range. Many thousands will be consumed by hawks, Ravens and other birds. Reptiles and other arthropods will take their share. Thousands more will die from the heat or fall victim to tire tread as they embark on a mass migration across the road. For those that survive predation and escape the human and environmental hazards, feeding continues until bursting.
Just prior to entering their final molt, the sphinx moth caterpillars will begin to burrow into the desert sand. There, they will molt into their pupa stage and again wait out time, temperature and humidity before emerging from the ground as a fully formed adult Sphinx Moth. You may notice these creatures, also called Hummingbird moths due to their large size and the noise they make in flight, around your lights at night.
We may see them again in large caterpillar numbers as the monsoonal summer rains bring heavy floral displays to the higher elevations, but a decade or more may pass before the valley bloom again gives rise to one of Mother Nature’s most successful “Flower Children!”
Watch Your Step!!
Photos and blog article by Ranger Steve