A Caterpillar Feast

In March, I journeyed back to the Anza-Borrego Desert in southern California. The big draw was an annual migration of Swainson’s hawks and the emergence of big colorful caterpillars, but as it happened, a third phenomenon blossomed simultaneously.

Big colorful caterpillars emerge every spring in Anza-Borrego.

They are the larvae of the white-lined sphinx moth and appear in various color combinations, from yellow with black stripes, to black with yellow stripes, to green with black stripes.

The caterpillars, sometimes called hornworms, feed on many types of flowers and plants, while the moths seek nectar.

The striking moths, also known as hummingbird moths, can be quite beautiful.

What I witnessed was the part of the life cycle when the larvae hatch and proceed to munch out on the desert flowers and plants.

It just so happened that this year the little guys were even luckier to hatch during a “superbloom,” a time when bountiful winter rains have produced carpets of wildflowers across the desert.

After eating nonstop and growing to 3-4 inches in length, the time comes for the next phase of their lives. The caterpillars burrow into the sand and pupate into a form that remains underground for 8-15 days. Then, the big transformation occurs and the moths emerge!

The moths spend their nights feeding and pollinating wildflowers, and then lay eggs on the undersides of flowers. The entire life cycle begins anew when the eggs hatch into very small caterpillars that begin to eat 24 hours a day on the flowers.

At the same time, Swainson’s hawks are making their way north from South America. They spend time in the desert around Borrego and have been known to feast on the caterpillars. Birders gather daily for the hawk watch. It was a gamble where or when they might be spotted. During my visit, I was disappointed to see that the hawks were in kettles a great distance away. Meer specks. I had expected to see them near the ground picking off the fat worms.

Unfortunately, I could not stick around long enough for the emergence of the moths, but I bet that’s something to see!

The superbloom, however, was a great treat.