Borrego Sun - Since 1949

Nature Watch: "Sphinx Moth Caterpillars"


Last updated 11/9/2023 at 1:03pm

Ernie Cowan

Those rare summer visitors to The Slot last week discovered they were not alone.

In the deep shadows of this narrow, eroded canyon in Anza-Borrego Desert State Park were thousands of colorful caterpillars that are the larval phase of the white-lined sphinx moth.

Borrego resident John Peterson was one of those visitors to make that discovery and shared it with the Borrego Sun.

"There were lots of caterpillars on top, and I think they were falling into The Slot and could not get out," Peterson said. "It was kind of raining caterpillars down in the squeeze as they dropped in."

This explosion of these large, colorful caterpillars is not unusual, but more typically a spring event, especially in years of heavy rainfall.

But this year has been anything but typical.

It was a near-record setting year from winter and spring rainfall, and then there were a couple of good summer monsoons and a tropical storm that dumped lots of water in the desert.

Likely this has triggered the life cycle of the moth that involves four life stages.

First there is the egg, and that hatches into the caterpillars that are marching about now.

When they have fattened up on available vegetation and grown to nearly four inches long, they will move underground or into sheltered places to enter a pupa phase in a cozy cocoon where a magical transformation occurs.

That transformation results in the emergence of a large moth known as the white-lined sphinx moth, but also called hummingbird moth because of its size and feeding habits that are similar to hummingbirds.

This cycle has likely benefited from the wet cycle that has produced lots of vegetation, much of which is not typically seen green this time of the year.

Peterson made another discovery on his summer hike into The Slot.

There has been a rockfall near the upper end of the canyon, making access to the most spectacular sections difficult to all but the most physically capable of scrambling over the huge boulder.

Peterson said he has notified the State Park and hopefully the boulder will be removed before winter visitors return to this popular destination.

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