Flying, Crawling Insects Inundate Southland Deserts : Nature: Butterflies and caterpillars apparently drawn by abundant plant life that sprouted during March rains.

Unusually large numbers of brown-and-yellow painted lady butterflies and green-black, white-lined sphinx moth caterpillars are swarming across Southern California deserts this spring--apparently feeding on the abundant plant life that sprouted after heavy March rains.

The butterfly is often mistaken for the monarch. Although its coloring is similar to its better-known relative, it is about a third smaller.

Lepidopterist Julian Donahue of the Los Angeles County Museum of Natural History, past president of the 1,500-member International Lepidopterist Society, noted that the painted lady is the most wide-ranging of the 12,000 to 14,000 butterfly species in the world. It is found on all continents except Antarctica.

“The painted lady is found year-round on the desert but in relatively small numbers except for years like this. When the huge populations build up, they migrate as they are doing now. We’re not sure what triggers them to head north, but we believe they are looking for new food sources.”

Donahue said similar butterfly population explosions have occurred only 11 times in this century, most recently in 1983.

“Nobody has worked out the dynamics of how the extraordinary buildup of painted lady butterflies comes about, but we think it is caused by a combination of factors--the weather and the quality and quantity of food sources created by the tremendous blooming of desert plant life this year due to the heavy March rains,” Donahue said.

Lauren Anderson, 82, an entomologist at UC Riverside and dean of butterfly and moth scientists in the Southland, said that for lepidopterists these rare population explosions and mass migrations of painted ladies northward are “the most exciting of times.”

“The butterfly lives from four to eight weeks,” he said, and during that time the females lay eggs “all the way from the desert along the coast clear up into Canada.”

As for the caterpillars--the larval stage of the white-lined sphinx moth--they are found in the desert every spring but in much smaller numbers, Donahue said.

The insects’ presence has been a source of consternation for desert residents and visitors whose vehicle hoods and windshields have been splattered with the butterflies. And desert roads are covered with thousands of green blotches from the huge caterpillars that are squashed by cars and trucks as they cross the pavement in search of food.

“Butterflies and caterpillars have been the talk of the desert the past couple of weeks. I have never seen anything like it,” said retired Western Airlines Vice President Jim Mitchell, who lives at the Palm Desert Country Club.

An ardent cyclist, Mitchell said riding his bike along country roads in unpopulated desert areas has become a risky endeavor. “The roads are slick where caterpillars have been run over. If I encounter a bunch crossing the pavement I weave in and out, trying to avoid squashing them and taking a spill on the slippery surface.”

Austin Stirratt, a resident of Flamingo Heights, north of Yucca Valley, said that he and his wife, Betty, have been sitting on their front porch watching wave after wave of low-flying painted ladies flutter by. “They stop and drink nectar from wildflower blossoms then continue their flight, all heading in the same direction,” said Stirratt.

National Park Service entomologist Jerry Freilich, based at Joshua Tree National Monument, said the butterflies and caterpillars may number in the billions, “when you consider they are all over the Southern California desert from the Mexican border to the Colorado River and beyond.”

Freilich said the painted lady’s feeding habits make its migratory patterns different from those of other species of butterflies--168 of which live in Southern California.

“The painted lady is very unusual. It feeds on nearly all wild flowers and bushes. . . . If heavier rains than normal happen and wildflowers bloom profusely and other conditions exist, these painted lady population eruptions occur,” he said.