The white-lined sphinx moth, also known as a hawk or hummingbird moth, can be found in Anza Borrego in the spring and after summer monsoon rains. It is a fairly common moth with a range from Central America to Canada. Most people visiting the desert see the caterpillar form, which voraciously eats some of the desert annual flowers during the daytime. It most prefers to eat the dune evening primrose and brown-eyed primrose plants, which are plentiful annuals after a rainy winter. The caterpillars grow quickly and can reach 5 inches in length. Their markings vary, but most of the ones in Anza Borrego are a mix of green and black; they range from almost all black to a mix of black and green stripes to the more rare mostly green form. The larger caterpillars can move quickly and will cross roads when looking for food. Once they are mature, the caterpillar digs a shallow hole in the sand by moving its upper body back and forth. It then pupates underground, with the sand providing protection while it waits for the right conditions to wriggle up from the ground and emerge as a moth. The adult moths mostly fly from dusk to dawn and look like a grey blur with a plump body and fast wings that hovers by a flower to feed before flying off to the next plant. From a distance they look like a tiny hummingbird. Both the moths and the caterpillars can carry pollen between flowers, helping to pollinate the plants and start the next generation.
During prolific years, there can be hundreds of thousands of caterpillars in the area northwest of Borrego Springs, such as off of DiGiorgio Canyon Road and Henderson Canyon Road. They will quickly eat the primrose plants before moving to the next area. As each female moth can lay hundreds of eggs, it doesn’t take very many moths to produce this many caterpillars. The migrating Swainson’s Hawks and reptiles will eat the caterpillars, but during prolific years this probably does not greatly reduce the caterpillar population.
Photos and blog by Barbara Swanson