What's that caterpillar?

This little fellow (or gal) was munching--quite contentedly, thank you--on the leaves of an aspen tree.

The homeowner didn't take too kindly to the critter defoliating his prized tree, newly purchased in Oregon and newly planted in Vacaville, Calif., so he asked us what it was.

Butterfly expert Art Shapiro, distinguished professor of entomology at the University of California, Davis, who maintains Art's Butterfly World website, identified it in a second.

"Smerinthus cerisyi, an exceedingly beautiful sphingid (nocturnal) with eyespots," he said. "Pupates in the ground and will emerge next April or May. Not native in Vacaville but fairly common in upland Napa, Sonoma and Lake counties and in the Sierra, Siskiyous, etc."

Shapiro surmised that the "eggs could have come in from Oregon."

So if you, too, have an aspen in your yard and are wondering what these little critters are, they will grow into a beautiful "One-Eyed Sphinx Moth" or "Cerisy's Sphinx"--if you let them.

"I encourage someone to rear them out rather than kill them," Shapiro says. "They actually won't harm the tree significantly. They'll also eat cottonwood and non-woolly willow foliage (not sandbar willow)."