Very mobile caterpillars go on prowl

There’s no doubt about it... it’s officially bug season in Green Valley.

The monsoon rains bring much needed green and growth to the Arizona desert, and with that, an abundance of creepy crawlers. Many insect larvae require moisture to hatch from their pupae, which explains why it seems caterpillars, beetles and other insects come out in droves after a heavy rain.

“I’ve never seen this many caterpillars before,” said Huguette Lusby, of the thousands of White-lined Sphinx larva that took over the backyard of her South Abrego Drive home Saturday and Sunday.

The caterpillars, yellow or green with black stripes, red dots, and a spiky tail horn (which does not act as a stinger), could be seen huddled in little groups in the shade of landscaping rocks, light poles and vegetation, trying to escape the heat of direct sunlight. Many others flocked to the Lusby’s swimming pool and hot tub, clinging to leaves and floating pool cleaners like rafts.

“At first they were in the yard, clearing out the weeds,” said David Lusby. “But then all of a sudden, they just headed toward the swimming pool, all of them. It was incredible.”

“One of the weird things about White-lined Sphinx larva is that they’ve got a drive to move around,” said naturalist Doug Moore, education director of Friends of Madera Canyon. “If they’re on one side of the road, they want to get to the other side.”

“I wouldn’t be surprised if in the next few weeks we start seeing this guys migrating across roadways in Green Valley and Madera Canyon,” he said.

“Bugman” Carl Olson, entomologist at the University of Arizona, says these mass migrations are a common sight late in the monsoon season.

“Why they have this mass movement is not really understood, but one suggestion is a search for better soil to burrow into for the purpose of pupation,” Olson wrote. “The desert plants that were their original food either grow in more clay-like soil, hard for digging, or have been depleted,” causing the caterpillars to search for more food.

In their adult form, the moths (Hyles lineata), which can lay up to 1,000 eggs, are some of the most important pollinators of desert plants in Arizona, he said. The larva are an important food source for local birds, especially Swainson’s Hawks, which come through the area specifically to feed on the caterpillars.

Olson says that at one time they even served as a seasonal food source for Native Americans who inhabited the Sonoran Desert.

“The Tohono O’odham would harvest these larvae, dry and braid them, and use them for food.” It makes sense, “because the numbers of caterpillars at this time of year made harvesting easy.”

jrichardson@gvnews.com | 547-9726