San Gabriel Valley hit by early surge of biting black flies

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Small black flies that are attracted to human breath and the salty moisture around the eyes are swarming parts of the San Gabriel Valley in California, experts say. The insects, which are smaller than mosquitoes but more aggressive, are biting residents and causing an unusual early surge compared to typical seasonal patterns.

Why it matters

The early arrival of these biting black flies is concerning for local residents, as the insects can be a significant nuisance and their bites are painful. While they do not transmit diseases like river blindness locally, the swarms are overwhelming communities and disrupting daily life.

The details

The San Gabriel Valley Mosquito and Vector Control District says the black flies, which thrive in fast-moving water, are targeting residents from Azusa to Altadena. Experts attribute the early surge to warmer weather and higher river levels creating new breeding sites for the flies. Vector control technicians are working to treat black fly larvae in local riverbeds.

• Typically, black flies appear in May with another surge in August, but their presence in late March is raising concerns.
• Experts say the current warm weather and higher river levels are creating new breeding sites for the flies.

What they’re saying

What’s next

Vector control technicians are targeting black fly larvae in local riverbeds, where the flies thrive in fast-moving water.