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What's Behind San Francisco's Plague of Flies?

A brief history of the California city’s hopeless battle against invasive insects.
Spotted-wing drosophila, aka vinegar flies, like the ones infesting cities in California.
Spotted-wing drosophila, aka vinegar flies, like the ones infesting cities in California.Blair Sampson/USDA

To walk while yawning in San Francisco is to risk getting a fly stuck in your gullet. The city is lousy with clouds of tiny, drifting insects, so much so you might think the roads are paved with rotten garbage.

“I feel like they come in evil waves in the city,” writes one local in a thread titled Screw Fruit Flies. “I got an infestation REAL bad,” complains another. “Was out of the apartment for a week, and my roommate had left some bananas out. There were tens of thousands, everywhere, in swarms.”