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Oak Worm

Brian Cabrera

Oak Worm


Summer Scourge of the Caterpillar Kind

Trees and Humans in Santa Barbara Must Deal with the California Oak Caterpillar


With the brilliant sunny days and balmy summer afternoons that have come to Santa Barbara, locals should be wary not to seek shade under just any tree. The oaks of the area have been struck with a plague of caterpillars that drop onto unsuspecting people, carpet driveways and park benches by the thousands, fall into pools, cover mailboxes, and show up in the least expected places. Not only are the caterpillars a nuisance for the residents of the area, but they also feast upon the leaves of our oaks, and in some cases, completely denude them of all foliage. Despite their radical affect on the area and the fact that most of us haven’t seen such scourges before, these creepy crawly hoards, according to Santa Barbara County’s entomologist Brian Cabrera, are a normal occurrence.

These caterpillars having been going at it for thousands of years,” said the county entomologist.
Click to enlarge photo

Brian Cabrera

Outbreaks of the native California oak caterpillar are a natural part of the insect’s life cycle. But because such population booms are relatively infrequent - occurring in 8- to 10-year intervals, according to the University of California’s Agriculture and Natural Resources website - people are usually surprised when they take place. Most react by “freaking out and spraying the ground where they see the caterpillars with broad-spectrum pesticides,” explained Cabrera, who works in Agricultural Commissioner’s Office. Broad-spectrum pesticides kill off not only the caterpillars but also the parasites that would naturally curb their population as well as other harmless insects like ladybugs and honeybees.

Oak Moth
Click to enlarge photo

Brian Cabrera

Oak Moth

The preferable line of action is to just let this natural cycle run its course, “but its hard to tell people that when they’ve got caterpillars dropping on their heads and into their pools,” said Cabrera. “It’s hard to tell people not to do anything.” When it comes to the trees, “as long as they were initially healthy, they should be fine,” he explained. “These caterpillars having been going at it for thousands of years.” For those who can’t manage to stand idly by while insects appear to wreak havoc on their backyards, the county entomologist suggests using water from a hose or a power sprayer to wash the caterpillars off their cars, driveways, and such. But be careful not to water oaks too much, Cabrera advised, because the trees normally get water in the spring from rains, so summer watering can result in root rot.

The best suggestion for people who do decide to use pesticides to fight these unwanted intruders is to choose pesticides that are specifically formulated to combat the California oak caterpillar so natural parasites and other insects are not unnecessarily wiped out. Cabrera also pleads for people to follow the label directions if they choose to use pesticides. But, bottom line, Cabrera said, “When people ask me, ‘If this was your tree, what would you do?’ I tell them I’d leave it alone.”

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