GV Gardeners: Where did the millions of caterpillers go?

One morning a few weeks ago, many folks in our area awakened to what appeared to be a world suddenly covered with yellow caterpillars. They marched in droves, apparently searching for something ... and eating as they moved along. They have now disappeared, or have they?

The bumper crop of fat caterpillars was the larvae stage of the equally fascinating White-Lined Sphinx Moth (Hyles lineate). These larvae can be up to five inches long, and have a prominent horn at the rear of their flashy bodies. When alarmed, they can rear up their heads in a threatening manner and may emit a thick green substance from their mouths.

These caterpillars prefer eating leaves of four o’clock plants, grape, tomato, portulaca, evening primrose, apple, and California fuschia. However, they have been seen consuming small weeds growing through sidewalk cracks. Pupation to moths takes place underground, so the larvae must dig shallow burrows to complete their life cycle.

Within two weeks the change to moth has occurred, and they must dig their way back to the soil surface. The moth then flies away in about 12 hours. Mating occurs shortly with females laying up to 1,000 eggs on the underside of the larvae food plants. Eggs hatch in a few days. In the Sonoran desert, there may be two broods per year, spring and summer. The male and female moth both die shortly after reproducing.

There are many species of these mostly nocturnal moths, but we are seeing the white-lined sphinx. The best time to view them is in evening, especially after a rain. Because of their fast flying pattern, they are difficult to photograph in flight. Sphinx moths are widespread from Southern Canada down through Central America, and are very common in Southeastern Arizona.

At first glance, many desert newcomers think they are seeing a rather strange hummingbird. The sphinx is recognized by its large eyes, furry brown body with white stripes, and pink underwings. Large for a moth, their body is 2-1/2 to 3-1/2 inches long, often with a wingspan of five inches.

Because of their large plump bodies and smaller wing surfaces, the sphinx must beat their wings very fast to stay aloft. These amazing flyers zoom about and then hover in mid-air as they sip flower nectar. Their flight manner requires abundant energy and produces a lot of heat. Therefore, they feed exclusively on nectar and eat from flowers which produce large amounts of water and sugar.

Their most preferred food is nectar from the evening primrose family. Other favorites are salvia, columbine, larkspur, honeysuckle, clovers, thistle, and Jimpson weed. The sphinx is very important in the pollination of petunias and evening primroses, especially the yellow evening primrose which opens at night only.

While hummingbirds prefer red, bright colored tubular flowers, these moths go for white and other pale colored tubular flowers which are easier seen in the evening hours. Since they do also feed during daylight, color preference may vary according to the time of day the feeding occurs.

Millions of yellow, white-lined sphinx caterpillars may have seemed overwhelming. Briefly they did eat plant material, but their real thrust was to find a soft burrow in which to continue their life cycle. Now after pupation, they have become lovely hummingbird look-alikes that are some of the most important pollinators in the Southwest.

Mary Kidnocker is a Master Gardener who writes frequently about the subject from a local perspective Her columns are featured each Sunday. She is currently president of The Green Valley Gardeners.